Dear Luciana:

The reason it did not snow has to do with the warm atmospheric temperature and we suspect it would get worse due to the continued rise of green house gases (GHG). There are always the possibility of natural contribution which cannot be ruled out completely however if you weigh the scientific evidence (95%) of these contributions come from the industrialization. A good place to start would be the IPCC2007 report, Climate assessment, Physical Basis. As you said you have strong science background, it would be good to read. I hope this helps.

Human being are responsible to trigger climate change off course by industrialization.

Not 100 percent change is the nature law we read our history from mollion years ago when there is no human snow can melt and nature creat favourable condition for human. Today secnario we can responsible for only create a favourable condition for climate change........

Anthropogenic causes have contributed more to global climate change. Emerging literature on limits and barriers to successful adaptation to climate change for example, targets human behaviour.

Precipitation formation takes place in clouds and is ruled by microphysical processes into the convective clouds. Solid precipitation formation needs cloud condensation nuclei and relevant atmospheric stratification. Human society greatly influence on nature and especially on climate but great portion of climate change ondoubtedly comes from nature processes as on Earth as from outer space.

Both human and natural factors have a role to play in climate change. This bc we only have control over our own actions but not over the natural. Human actions fastens the processes of climate change which makes it difficult for natural systems to adjust to such rapid changes. Nature has a way of healing its own wounds but the rapid changes associated with human induced change does not give nature enough time to correct these anomalies. Therefore, the present climatic changes we are witnessing cannot be attributed to only one factor but the combination of the two (nature and human).

Let us be cognisant of climate variability. It is normal that it does not snow once in a while. It is part of nature-variability. Of course everyone in that part of the world looks forward to snow during Christmas. Let us draw such conclusions of climate change only after long term studies have proven trends.

Perhaps the greatest cause that climate change issues is emerging is definitely for human society and their security. The natural changes are imperceptibly slow (perhaps) its human as a most developed species are more susceptible to stress and shocks induced by climate variability. I think for natural changes human can adopt (as they have been evolving since evolution of human species) but for the ongoing changes which is referred to caused by human are often seen unbearable and human society are inventing and innovating ways to adapt to the changes. And perscribing ways to mitigate as well.

Climate variability is part of nature, of course - man-made climate change does not "impress" by how much the climate is changing, but how fast this happens. In general, in the end it does not matter why all this happens, because the fact that we are in urgent need to adapt to the effects remains!

I don't believe that climate change is because of human activities. We must not forget the 11years circle of sun. These cliamte changes occur in earth many years ago and will be continued to happened. Human activities is a factor and might accelerate these phenomena but not in a great extent. In my country this winter might be the worst for the last 15 years at least!! Sun's acivities influence the earth climate in a great extent and we cannot do many things for that. We can be responsible to the environment and protect it. However, i can't believe in the green developent etc...because suddenly we discover that we can change what is happenning. There is a great economy industry that relies on the pollution and a lot of money which exchanged for this reason. We can also not forget that goverments cannot agree for important isuues (for example Kioto and most recently). It is in our hand, individually to protect the environment and not expect from goverments. As for sun activities we must be patient and be prepared for anything!

Dear Lutiana, I recomend the Book (Flyer in attachment) from Frank Sirocko (Hrsg.) Wetter, Klima, Menschheitsentwicklund - Von der Eiszeit bis ins 21. Jahrhundert (Weather, Climate and Development of men - from ace - age to 21 Century . Its in German but very helpfull for unterstanding natural and anthropogen componentes. Jürgen Gauer

For me is a natural process: see this link: http://news.opb.org/article/to_catch_a_glacier_thief_follow_the_ice_cubes/

The average state of the global climate over the past 30 years, results from the interaction of several factors (forcing) of natural and anthropogenic origin, it is the Global Climate System (GCS). Although we did not also able to identify the role or the degree of impact of each factor individually due to interactions of the second order which take place in GCS, on the other hand, the current warming cycle became noticeable after the Industrial Revolution when the increased concentration of greenhouse gases increased by anthropogenic inputs. I believe that we do not have a method by which it can be said definitely, but there is strong evidence that the action appears as a forcing antropogêncica increasingly relevant to the average state of the atmosphere. Remember the precautionary principle "when in doubt the better option is the most conservative."

Evidences show that anthropogenic forces are related to some GHG emissions, but in my opinion (and in my research area) this is not the most important question. The turning point for this debate is: are each societies in the world prepared to face the impacts of climate change? Climatologists or natural sciences must look after some responses, but regarding the social dimensions of climate change, we must recognize different vulnerabilities, resilience tools and antecipatory adaptation policies. No new environmental problems will be created, they will just be amplificated.

Both! But I think more natural causes ...

Climate change is caused by both natural and human causes but that due to natural causes has during the evolution of the earth been kept in balance by the evolutionary process. The human contribution to climate change is due to the upset in balance in greenhouse mainly due to accumulation of carbon dioxide emitted from burning fossil fuels and this is made worse by human reduction of the capacity to absorb Carbondioxide due to activities like deforestation. The lack of snow observed by Luciana most likely has a contribution from natural and human causes. We are however unable to control the natural causes and we should therefore take measures to reduce the addition of green house gases that are caused by human activity which we have some capacity to control and whose negative impacts should not be overlooked.

Almost nobody thinks that human activity has no influence in climate. Climate has been changing for many millions of years, but human activities apparently caused some additional change in recent times. The discussion that persists is not about the existence of climate change, or about the existence of some human influence on it, but on the relative magnitudes and the timing.

The most recent report of the Intergovernmental Panel on Climate Change (IPCC 2007) estimates that the human influence, especially through greenhouse gases (GHG) emissions, is unequivocal. They also say that it is "very likely" that "most" of recent change is of human origin, but this assertion is regarded by many as relatively vague: "most" in this case may mean 50.5% probability or 99% probability; "very likely" is a statement based on a subjective assessment of a variety of methods, many of which are the object of fierce discussion and are affected by wide uncertainties.

Among the points that are affected by large uncertainties is, for instance, the coefficient known as "climate sensitivity", meaning the temperature rise that would be caused by doubling the atmospheric concentration of GHG. These gases by themselves have a sensitivity of about 1.1°C, but the total net effect can be increased or attenuated by "feedbacks". The IPCC estimates that the balance of positive and negative feedbacks is positive, so that sensitivity would be above 1.1°C, possibly between 1,5°C and 4.5°C or so. Among these feedbacks are: (1) less area covered by ice and snow reduces reflection of heat to space (albedo), and this is a positive feedback enhancing the effect of GHG; (2) increased temperature mean more evaporation, and part of this evaporation would go into additional clouds; atmospheric water vapor may enhance the warming effect because it is a GHG; but on the other hand clouds reflect sunlight back to space (i.e. they have an albedo), causing temperatures to be lower whenever it is cloudy; an increase in cloud cover would attenuate warming (a negative feedback). How much would cloudiness change with GHG, and the net effect of clouds on sensitivity, "is not well understood", says the IPCC and most scientists concur: this sole factor may cause the net overall feedback effect to be positive but much lower, or even turn it negative, thus greatly reducing the degree of warming.

Even accepting at face value the estimates of the IPCC on climate sensitivity, their projections of future climate change are based on "scenarios", i.e. imaginary futures for population and technology causing more or less increase in GHG emissions in the future. These scenarios are not "predictions" of things to happen, but "projections" based on a certain "scenario storyline", and nobody knows the probability of the various scenarios. Specific projections are based on a scenario providing numerical inputs to mathematical models of the climate, where many variables interplay in a varied manner according to each model's assumptions and structure: even for the same scenario, various models predict different outcomes, and the average of the ensemble of models is not necessarily a good estimate (e.g.: simply adding a new and more extreme scenario, or using some additional mathematical model for the same scenario, would change the projection).

In 2010 the UN Secretary General asked the Inter Academy Council (a body formed by most national academies of sciences) to evaluate IPCC internal workings. The IAC found that uncertainties had been systematically underplayed in IPCC publications, especially in the "Synthesis Report" and one of its parts, the "Summary for Policymakers", where very uncertain assertions were made with ostensible disregard for underlying uncertainties. It also found severe defects in the IPCC report on impacts (working group 2), and a general lack of sufficient transparency in the internal workings of the IPCC and in its communication of uncertainties to governments and to the public at large (the IAC report can be read at http://reviewipcc.interacademycouncil.net/report.html).

Besides the large uncertainties about climate projections as such, there are indeed yet wider uncertainties about the impacts of climate change. Indeed, the impact assessment by IPCC is the weakest link in its synthesis of scientific knowledge about climate change. Many gross mistakes have been found in the report by IPCC Working Group 2, on Impacts and Adaptation, some of which have been reluctantly corrected (after first firmly denying that they were wrong), for instance the claim that all the ice on the Himalayas would disappear by 2035, or that more than 40% of the Amazon forest would turn into a savanna in a few decades.

In some aspects, the IPCC impacts report was more prudent, but voices outside the IPCC have often opted for more exaggerated claims. For instance, the IPCC projection of sea level rise during the 21st century is a total rise of about 34cm (average of the various scenarios). The range of the central projections of sea level rise for all scenarios is between 28 and 42cm, and the envelope of the uncertainty margins, i.e. the range between the lower bound of the projection for the mildest scenario and the upper bound of the projection for the warmest scenario, is between 18 and 59 cm, all distributed along a hundred years. This average projection of 34cm in a century or 3.4 millimeters per year (compared with about 20cm rise accumulated in the previous century) seems right for the recent period of very precise satellite measurements of sea level: the recent speed is about 3 mm/year along two decades, with some deceleration in recent years.

But such moderate rises in sea level are hardly worthy of an alarming headline, and are seldom cited in the press: many popular versions of the problem report (and even graphically describe with photoshopped pictures of an inundated Manhattan) much more dramatic sea level rises, but without much scientific basis. For this reason one must always distinguish between the IPCC itself as a summary of existing scientific knowledge, or better still, direct reading of the original scientific research synthesized by the IPCC, on one side, and (on the other side) the "popular version" given by less scrupulous commentators including headline-hungry journalists and environmental advocacy organizations.

To assess impacts it is useful to look back to warmer periods in history, to see whether a warmer climate caused the expected consequences (even if such past warming had of course not been caused by human-emitted GHG). Warmer periods in some regions have been ascertained (for instance, the Medieval Warm Period during which, at least in some parts of the world, temperatures were well above current levels, which allowed Vikings to colonize the green and fertile prairies of an island they called Greenland, which they abandoned when the warm period ended several centuries later and Greenland was no longer so green): the presumed melt of Greenland glaciers at the time does not seem to have caused much troubles elsewhere (Venice, for instance, flourished on its low-lying island during precisely that time).

There is currently a debate on the reliability of models to predict climate in view of the lack of warming on a global scale during more than a decade: the trend in global average temperatures from 1995 to 2012 is practically flat, oscillating with no discernible trend and interrupted only by the occasional spike caused by a recurrence of the cyclical El Niño phenomenon (like the strong one in 1998). Similarly flat trends are observed regardless of the initial year chosen, e.g. 1995 or 2000 or 2001.

Of course the 2000s are still the warmest decade, since the flat trend has occurred after a period of warming (if you climb to the roof of a skycraper and then start walking around the rooftop, you are no longer ascending but you are still at the highest level, even if you remain there for years).

One decade of no warming does not mean that no global warming is occurring, nor it negates the validity of the GHG effect, but it may put in question various assumptions in the models so far used: the lack of warming on the surface of the Earth means that (if the amount of heat trapped by GHG is as large as models estimate) the heat not warming the surface may be "somewhere", or else the estimate of the amount of trapped heat was wrong. Some scientists have speculated that the "missing heat" may be, for the time being, stored in the deep ocean, but that is just an hypothesis with little scientific support. Other scientists are revising the models themselves, in order to account for the apparently missing heat. If the lull in temperatures persist a bit longer it may throw the whole set of models into question.

Another problem has arisen with satellite precise measurements of temperatures high in the atmosphere: according to the usual models, as the surface gains warmth the higher atmosphere should get cooler, but apparently it is not happening. This is another cause of concern prompting scientists to revise their models.

Science is made by perpetual debate, based on facts and hypotheses, in order to interpret a reality that is always messy and confuse. As one American president once famously quipped: "Predictions are difficult, especially about the future". Scientific knowledge is always provisional and subject to revision. And the best attitude for scientists is to be open to new ideas and new facts, and to be ready to revise their conclusions at every point. Politicians, believers and activists are moved by faith, value judgments and unmovable convictions. Scientists are moved by evidence and doubt. Or as Robert Merton put it in his classic work on the normative structure of science, "organized skepticism".

Most of recent studies on climate change ( including IPCC guidelines) show that emissions of GHGs (greenhouse gases such as C02, N2O, CH4) are the main cause of the rapid global warming during the last decades - as described by the previous comments . Actually, international agreements try - with no success - to fix economy-wide emission reduction targets for developed countries and mitigation strategies by developing countries, in order to keep global warming below 2°C above the pre-industrial temperature.

Building a low carbon economy is probably the first step to reach a binding global change agreement; the key components of the future treaty include: Mitigation strategies and a framework of rules on compliance; a framework for action on adaptation to climate change; REDD and REDD+; LULUCF; NAMAs; definition of the role of carbon markets; international cooperation on technology improvement and energy saving; alternative farming systems; strengthened rules on monitoring and reporting and verification. All these steps need fast start fundings to help supporting low carbon strategies.

For futher details see: http://ccaqu.jrc.ec.europa.eu/home.php

Other minor theories (I mean less known theories) exist about climate change: they questioning that human contributions to global warming could not be scientifically demonstrated - due to the limited temporal series used - they suggest that a gradual cooling is expected to arise in the next future, due to natural driving forces, such as the Pacific Decadal Oscillation (PDO), solar radiation, ect. Some of them suggest that the linkage GHGs-climate change is only a mere pretext to make easy money through the carbon-market.

i think Climate change caused by both natural and human

I notice that many contributors in this thread limit themselves to the expression of their general "belief" regarding climate change.

But this is Researchgate: this is not the proper place to state personal beliefs, but to discuss scientific research. Climate change has become for many almost a religious belief and a political "cause", but we should keep a cool head.

Also, I think posing very general questions (such as the one motivating this thread) is not very useful: scientific debates are about more specific issues. The scientific devil is always in the details. In other spheres of life one can pose wide-ranging questions (such as "Does God exist?", "Do we have free will?", "Is democracy good?", "What is the meaning of life?" or "Am I in love with this person?"), but in science such wonderings are not quite useful, and often they simply betray ignorance of the matter.

Since this website is on Research, let me recall what I once read in a book on scientific methodology: one can do research only on subjects one already knows and is familiar with: unfamiliar subjects must be the subject of study, rather than research.

Once you are familiar with a subject area, and have absorbed the state of knowledge and existing debates, your questions are likely to be more "educated", i.e. less general and more specific, and those questions are the ones that count. They are interesting questions also for other experts in the field. And if your questions have not yet been thoroughly investigated, or no satisfactory answer has been provided, then you have a subject for your own research. And only the most accomplished experts in a field (such as Einstein or Stephen Hawking) can dare to ask a general question about their field, such as "What is matter?"" or "Will the Universe come to an end?"

Posing rational challenges and questions, besides, is the essence of scientific progress. No matter is "settled" even if most scientists agree with a certain view (examples abound in the history of science). Science progresses by asking original and educated questions, highlighting unexplained anomalies in existing accounts of reality, and addressing them armed with the scientific method.

Climate Change is a phrase created by human intelligence to give a meaning to his observations on environment and its evolution.

just a reminder of the fact that in a recent study by the climateanalytics, a research organisation based out of Europe, we were left with 1000Gtons of CO2 by 2050 to limit our temperature rise below 2degree C. But between 2000-2009 we have utilised one third of the CO2 emissions. This primarily are sourced out of human induced emission activities, as per the IPCC findings. Mostly the sources of emission lie in the emission intensive modes of productions which are driving the economies over the decades across the world. There is a strong reason to believe the need for de-coupling this emission intensive economic growth performances. it is human induced as the decisions of such activities are induced by human.

Both,but,I think,we the human,create the more causative impact.

Tirthankar,

first one needs to recall that the exact calculation of the relationship between emissions and temperatures, and the time span needed for a given concentration of GHG to reach the "equilibrium" rise in temperature (as distinct from the transient or short term effect) is plagued with wide uncertainties. But most importantly, have you any idea of how emissions can and would actually be limited by the amount proposed, not in an ideal world but in the real one? My guess based on recent trends and existing calculations of costs and benefits is that nothing of the sort is likely to happen. So we better think of something else, e.g. how best to adapt to the expected changes in climate.

Some of the changes will probably need some effort for adaptation against negative impacts. For instance, if desertification happens in some arid tropical territories like the Sahel, people will accelerate emigration from those territories, looking for employment elsewhere (as many of them are already doing). Except if the Sahel, which had been desertifying before, continues its recent "greening" (goggle "greening of the Sahel" for relevant literature).

In other cases, the impacts may be positive; for instance, vas amounts of land will become more productive in temperate middle latitudes, i.e. North America, Northern Europe, Central and Northern Asia, and the Southern Cone of South America: the no-frost period will be longer, and thus the growing period for crops will also be longer. Besides, in all latitudes a greater concentration of CO2 in the atmosphere will lead to higher crop yields (increased photosynthesis), especially in C3 crops like wheat, and a great economy of water in C4 crops like maize: C3 yields may increase by at least 20-40%, and water requirements for C4 crops, as CO2 concentrations rise from current 390 to about 550 parts per million, may be reduced by 25 to 80 percent depending on plants, varieties and other environmental variables. Maize yields in semi arid countries such as Mexico or Northeast Brazil may end up increasing thanks to climate change. The amount of arable land is already increasing, and its yields augmenting, both in Northern US, Canada or Argentina. In the latter country, where I live, the shift of precipitation isolines about 200 km to the West and North has increased total agricultural land (grazing or arable) by about 2-3 million Ha, and cultivated land (for cultivated pastures or for annual crops) by about 8 million Ha. Observed shifts of temperature isolines towards the South in Argentina allows now to produce wine in Patagonia, among other novelties. These shifts of rainfall and temperature lines in Argentina have already occurred in the latest 30-40 years: scientists are not sure whether it is a result of anthropogenic climate change or is a result of natural variability, but it provides an example of beneficial effects of warming upon agriculture wherever the main constraint is cold, not heat, and wherever increased evaporation leads to increased precipitation.

Other adaptations require some investments. For instance, levees around New Orleans (famously not cared for before Katrina) will probably need an extra feet or two to fend off a rising sea; many levees in the polders of the Netherlands have already that extra height, but some will need an additional layer (to be gradually constructed along one hundred years!!!). Low-lying costs with minimal slope (let us say 1%, meaning one meter up in the first 100 meters ashore from the high tide line) may lose 30-40 meters as per the IPCC projections. Slightly more steep coasts, which are more common (3-5% slope or more ) would lose much less. Coasts with less than 1% slope in the first 100 meters are rare, and rarely inhabited: they are mostly found in swamps and mangroves. Few such flat coasts are devoted to agriculture in the vicinity of the water (soils are too saline). Some fishing wharves would have to be moved if water rises, some beaches will disappear or become narrower: Some beachfront luxury homes will need their floors to be built at half a meter extra height.

Places that were thought to be at great risk are not necessarily so: local sea level is determined not only by global sea rise, but also by local tectonic movement (subsidence or emergence of land substrate), and also by sediment deposition and movement. The low coastal lands of Bangladesh, for instance, are actually gaining in area and elevation due to continuous deposition of abundant sediment from the Ganges River and its tributaries, as has been the case for millions of years while the former Ganges estuary was filled with land and became a delta. This accretion of sediment is not offset by the lower amounts of sediments slowly carried out to sea by water movement.

Land is rising in many parts of the world (e.g. in Scandinavia), countervailing any rise in sea level.

100 years or more is time enough to face those problems. And fossil fuels will not last forever at the current rate of usage: cheaper sources of energy (including safer nuclear plants plus other viable ideas) will probably proliferate.

Humankind will have these and other problems to solve during the 21st (and 22nd) centuries, but they are not cataclysmic and human ingenuity will probably be able to prevail. The day of Doom is not nigh.

Stefan Rösner says that "Models tell us that the temperature increase since the about the 1970s can only explained when human activities are included." Actually, models tell us nothing: models are instruments of analysis, loaded with assumptions. The same data may "tell" different stories if loaded into different models. Data+current model assumptions suggest human emissions have something to do with that wave of rising temperatures, but they do not tell us in what proportion (the assessment that it is "very likely" that "most" of the increase is human in origin is a rather vague subjective judgment based on the outcome of many different models with different assumptions, and says actually little).

Data are continuously expanded by new data, and old data can be corrected for newly discovered errors in measurement or methodology. Most importantly, assumptions built into the models are also subject to adjustment and change, especially when new facts do contradict the model's predictions.

For instance, existing models did not predict beforehand that global temperatures would show a nearly flat trend since 1995 to the present, even as GHG concentrations go incessantly up. This fact is not as yet a refutation of the models, but a sign that something is amiss and needs adjustment. We can guess some ex post explanation (e.g. the heat may be hidden in the deep ocean), but that ex post explanation is ad hoc, and was not in the model. The outcomes of Sunday football games are easy to know if you read the Monday newspapers, but the idea is to forecast them before they happen.

As we know ever since Popper, scientific theories can (sometimes) be refuted, but they cannot be verified or confirmed (another theory may always explain the same facts).

As new data keep coming, models need to be revised, to provide (for instance) some explanation, still non existent, for the "missing warming", something that becomes more pressing with every successive year of nearly flat trend. Sciences progresses by pointing to unexplained anomalies in existing models (like the retrocession of Mars that went unexplained in pre-Copernican Ptolemaic astronomy), and by providing new explanations that explain as much or more than the previous theory, and also explain the anomalies.

This is not to say that humans do not contribute to warming through greenhouse gases, but as I said before, the devil is in the details. And our ignorance is great,

Temperature variability is due to the earth dynamics around the sun. Perturbations are due to Human activities. Climate change is due to a continuous and drastic change in temperature. It is then important to study the natural contribution of the sun in the temperature variability, the global contribution and finally the Human contribution. The external forces acting on our planets are very important compared to forces due to Human activities. Climate change is then most natural.

It is a two-faced issue on this. One, as a result of human activity and second, it is a naturally occurring phenomena.

My studies in GHG made me be sure that human society has biggest guilt on climate changes issues. It is just a bit contraditory that some articles that points to other causes like "natural causes of the world" have a big impact in world midia, it makes me think that we must take actions to stop producing GHG exaggeratedly and also take actions about the other causes of this issue.

I thank everyone a lot for your answers, it was enlightening for me. I also liked the opinion of your own "beliefs" because I made this question trying to have the opinion of people in general, not only experts of climate area (as I´m not expert in this area). Sorry if I bothered you with this, Mister Hector Maletta... I liked you conclusion "100 years or more is time enough to face those problems. And fossil fuels will not last forever at the current rate of usage: cheaper sources of energy (including safer nuclear plants plus other viable ideas) will probably proliferate.

Humankind will have these and other problems to solve during the 21st (and 22nd) centuries, but they are not cataclysmic and human ingenuity will probably be able to prevail. The day of Doom is not nigh".

We have time to solve this problem but I hope that we won´t have to be "facing the abyss" to start take real actions to solve this problems.

Ya absolutely, Climate change is as a result of HUMAN activity as well as natural process...

I aggree with those who think that climate change is due to both human activities and natural process.

I think the discussion of what is to blame for the warming trend and increase in temperature variability is fine from an academic standpoint. However, once the media gets hold of any announcement and starts pointing the finger in the direction of blame people get upset. So much so that in the agricultural community producers will leave the room at the mention of "climate change" and often this is due to the association with various political groups. I doubt if there will ever be convincing proof of why there is change in the climate. What might be a more productive focus is to concentrate on how we as humans might reduce carbon emissions to offset any disturbance regardless of the cause.

I am happy to notice that this is a kind of polemic subject. I thought I was being bad informed about this issue here in Brazil, but I can see that this is not a question that can be solved so simply, like saying: human has 89% of guilt and nature has 11%. I know this is wrong to try to make things so simple, but it would be great thing to show on midia... simple information spreads more easily to everyone.

Climate is for me an interesting area of study, we know the fact that temperature is changing and we suffer from consequences, but it´s difficult to know exactly the causes, even for old events like El Niño and La Niña we still have doubts about the causes.

Maybe it´s a general thought to blame big companies about our ignorance on many environmental issues, but it´s a fact that we must control GHG. As a technician of environmental sciences I can only do my job working against production of GHG, but hoping that someday we can go directly to all causes of climate changes (and have the exact information to show to everyone).

The present earth warming up is often explained by the atmosphere gas greenhouse effect. This explanation is in contradiction with the thermodynamics second law. The warming up by greenhouse effect is quite improbable. It is cloud reflection that gives to the earth’s ground its 15 °C mean temperature. Since the reflection of the radiation by gases is negligible, the role of the atmosphere greenhouse gases in the earth warming up by earth radiation reflection loses its importance. We think that natural climatic oscillations contribute more to earth climatic disturbances. It is known that earth is subject to various climatic oscillations of relatively short periods such as the twenty-four hour and the one-year climatic oscillation periods. The other oscillation that we hypothesize to exist has a longer period (800 to 1000 years). The glacier melting and regeneration cycles lead to variations in the cold region ocean water density and thermal conductibility according to their salinity. These variations lead one to think about a macro climate oscillating between maximum hot and minimum cold temperatures. This oscillation is materialized by the passages of the planet through hot, mild, and cold eras, leading to the great season climatic oscillation phenomenon (GSCO). Thus, our planet lives four great seasons a great spring, a great summer, a great winter and a great autumn/fall, making a great year embracing our four small classical yearly seasons. This great season climatic oscillation is responsible for the slowing of the thermo haline circulation (THC) to the North Atlantic signaled by several authors. Culminating great summer heat weather maxima would take place around the years Ns = 2000 ± (800 to 1000)k and culminating great winter cold weather maxima would be expected to occur around the years Nw = 1600 ± (800 to 1000)k, where k is an integer number. The probabilistic character of the parameters that are at the origin of this climatic oscillation makes the long-term prediction less precise but the deterministic tendencies and the resonance phenomena give precious information on our planet climatic future. The present warming up is well interpreted in the frame of the great season climatic oscillation theory. The macro climate of the Maghreb and Europe countries is strongly influenced by this great season climatic oscillation.

1) The Great Season Climatic Oscillation, A. Boucenna, I. RE. PHY. 1(2007) 53

2) Pseudo Radiation Energy Amplifier (PREA), A. Boucenna, International Review of Mechanical Engineering (I.RE.M.E.), Vol.5, n. 5 (2011)1000-1005.

3) The Great Season Climatic Oscillation and the Global Warming, Ahmed Boucenna, arXiv:0808.0897 (August 2008)

Boucenna,

the existence of the greenhouse effect is something that has been repeatedly confirmed experimentally. I am not a specialist, but apparently the idea that the greenhouse effect violates the 2nd law of thermodynamics is not true. The idea that (other things remaining equal) a higher concentration of CO2 in the atmosphere will cause warming is also generally not disputed, even by skeptics (that is, for scientifically informed skeptics). What is disputed are a number of details:

(1) the size and signs of the feedbacks: doubling CO2 would increase global temperature by about 1°C, but the official estiomate of the IPCC is that this would trigger some feedbacks (e.g. more water vapour in the atmosphere) enhancing the effect, so that climate sensitiviy (= degrees Celsius of difference caused by doubling the CO2 concentration) would be around 3°C instead of 1°C; several strands of argument suggest this is an exaggerated estimate of sensitivity, especially because it underestimates the cooling effects of increased cloudiness (caused by more vapour in the atmosphere, and more aerosols emitted with the same greenhouse gasses).

(2) the instrumental record for temperatures may contain a bias, because many stations are being increasingly surrounded by heating objects (buildings, cement, engines, etc.) so that not only are they hotter than they would be in the absence of those local heating sources, but also their TREND is a more accelerated warming, because the local heating sources are increasing over time.

(3) many of the claims are based on a very short period of warming (e.g. 1970-2000), but a longer record indicates some warming but much less than in that period: temperatures tended to increase in 1850-1880, they stalled or decreased in 1880-1915, they increased in 1915-1940, they stalled or decreased in 1940-70, they increased in 1970-1998, and they stalled since the late 1990s until (at least) 2011. In all this period, besides, there was an underlying (but small) tendency to increase from one cycle to the next, because the world is recovering from the Little Ice Age (which cooled the planet from the 14th to the 19th centuries, after the Medieval Warm Period that warmed it between 900 and 1300 approximately).

Thus indeed the planet has been warming in 1970-98, at an annual or decadal rate practically equal to the rate observed in 1915-40; with alternating cooling and warming every (approx.) 30 years. It is also slowly warming (about 0.7°C per century) on a longer time scale, as it recovers from the Little Ice Age, since approx 1850. And the rapid warming since 1970 ended before the year 2000: the trend is practically flat since 1995 to 2012, or since 2000 to 2012. In the latter 15 year there were only two "peak" years in 1998 and 2010 due to strong El Niño phenomena, but there is no evidence that El Niño cycles would be affected in any way by global warming or by CO2.

Projections for the future have been based on the above estimate of a high sensitivity (3°C), but this assumption has a very large uncertainty and there is growing evidence that it may beoverestimated. Projections are also based on models loaded with a number of assumptions not necessarily coherent (for instance, they assume high economic growth but at the same time some of the scenarios assume high fertility levels and thus high population growth, when it is known that fertility and income are inversely related, and fertility is rapidly falling across the world.

And finally, the problem is not the warming itself, but its alleged consequences, and many estimates of the impacts are overblown. If the oceans rise by 30-34 cm in a century (the IPCC central projection, with margins from 128 to 59 cm per century) some specific areas may need extra protection, such as New Orleans or Venice, and some extremely low islands in the Pacific may disappear (though the latter is hotly debated). But mankind could adapt to most of the impacts with relative ease. E.g. the sea level rose about 20 cm during the 20th century, but no catastrophe befell coastal areas anywhere in the world, and has been rising at a speed of about 25-30 cm per century according to recent measures by satellite altimetry, with a tendency to rise more slowly in recent years: this are speeds well below the speeds projected by models back in the 1990s.

General advice: exercise a certain level of skepticism in this matter, especially for projections going far into the future. Science is based precisely on this: do not take anything for granted, question everything, look for data and rational argument, even if you do not like the results.

Hector Maletta

1) You affirm that you are not specialist, and You confirme that :

The existence of the greenhouse effect is something that has been repeatedly confirmed experimentally. I am not a specialist, but apparently the idea that the greenhouse effect violates the 2nd law of thermodynamics is not true ?

2) I confirm that :

The green house effect is not confirmed experiment and I confirme that the greenhouse effect violates the 2nd law of thermodynamics.

G. Gerlich, and R. D. Tscheuschner, 2009. Falsification of the Atmospheric CO2 Greenhouse Effects within the Frame of Physics,

International Journal of Modern Physics B, Vol. 23, No. 3, 275-364 (2009).

3) You pass directly, as the so-called specialists of the IPCC make it, to the relation between the increase of the CO2 in the atmosphere and the climatic warming up.

You say that if the concentration of the CO2 in the atmosphere increases the mean temperature then increases. It is false.

Actually, it is the concentration of the CO2 that increases if the mean temperature increases (the CO2 is freed of the waters of the oceans) and if the mean temperature decreases the concentration of the CO2 then decreases (the CO2 is captured by the waters of the oceans).

4) La théorie des GSCO explique lest l’histoire des changements climatiques depuis 12000 années.

The GSCO theory explains the climatic changes history since 12000 years.

A. Boucenna, The Great Season Climatic Oscillation, International Review of PHYSICS 1(2007) 53-55.

8) W. Dansgaard, S. J. Johnsen, J. Møller, and C. C. Langway, Science 166 (1969) 377

Thanks for your comments, Ahmed. Very interesting.

This exchange has clearly shown that matters regarding climate change are far from been settled among scientists. The "consensus view" reflected in IPCC report has many dissenters, which dissent to different degrees.

I am certainly no fan of the IPCC, but I am also aware that your views are not shared by many scientists that are profoundly skeptical about the IPCC conclusions. I have read the work of many skeptics and critics of the IPCC that nonetheless accept the idea of the greenhouse effect, i.e. that gasses in the atmosphere trap heat and keep it from escaping to space, which (they say) explains the average surface temperature of Earth (about +15°) as compared with an astronomical body without an atmosphere (e.g. the Moon, where average temperature is about -18° in spite of being at the same distance from the Sun than the Earth is). That difference of about 33°C is, they say, due to the greenhouse effect of gasses in our atmosphere, primarily water vapor and also other gasses such as CO2. What is mostly disputed by those skeptical scientists is the magnitude of the recent warming and its timescale, the share of that warming that is due to changes in greenhouse gasses, and the share of the latter portion that is in turn caused by human-caused emissions. There are, of course, also other skeptical views that dismiss the greenhouse effect in general, but I am certainly not qualified to enter this specialized terrain.

Besides the substantive points of the discussion, one important lesson is that the science of climate change is not a settled field where every scientist is in agreement, but a field in which a multitude of hotly disputed issues exist, and where great uncertainty reigns regarding any specific or alternative theory that is proposed, and regarding any prediction or projection derived from those theories. There are several views defended with equal vigor and assertiveness by the scientists proposing each of them.

A prudent layman should, in my view, remain prudently skeptical until the fog of battle settles down.

Hector Maletta

Concerning this :

“I have read the work of many skeptics and critics of the IPCC that nonetheless accept the idea of the greenhouse effect, i.e. that gasses in the atmosphere trap heat and keep it from escaping to space, which (they say) explains the average surface temperature of Earth (about +15°) as compared with an astronomical body without an atmosphere (e.g. the Moon, where average temperature is about -18° in spite of being at the same distance from the Sun than the Earth is). That difference of about 33°C is, they say, due to the greenhouse effect of gasses in our atmosphere, primarily water vapor and also other gasses such as CO2”.

I invite you to read my recent paper :

The Pseudo Radiation Energy Amplifier (PREA), A. Boucenna, International Review of Mechanical Engineering (I.RE.M.E.), Vol.5, n. 5, July 2011

Abstract

“In this paper we show that a gray body which separated from vacuum by a material interface and submitted to outside incident radiation can behave like a Pseudo Radiation Energy Amplifier. The Earth (Earth + atmosphere) is not a simple isolated gray body but it is in fact a Pseudo Radiation Energy Amplifier with adequate reflection coefficients. The balance of the energy exchanged between Earth and outer space is reconsidered and the estimated Earth’s ground temperature mean value 15 °C is then derived”.

If you send me your email, I send you this paper. My email : [email protected]

I don't personally know whether some climate change is linked to human impacts or not? What I would say is that if we continue to damage our ecosystems we are thereby damaging ourselves. In other words, it is in our interests to do something on a personal, local or global level. We share the earth with nature and live alongside it and common sense tells you we should not hurt natures ways as it will endeavour to hurt us back. My blog naturestimeline tracks the seasonal changes and once you appreciate the yearly differences you can start to see patterns emerging. Whether these patterns or trends are long term, it may be too early to tell and it may need tens or hundreds of years of data to back up any evidence. I do feel that as humans, what we will all continue to do is to argue for or against AGW etc. and in turn, not resolve anything.

Kind Regards

Tony Powell

http://naturestimeline.wordpress.com/

ps! I am no expert within this field and furthermore these only indicate my personal opinions. I suppose, I best read the 42 other comments on this thread.

Tony Powell

Yes. What I say, are the conclusions to which I arrived. They are not in contradiction with the noble causes to save our planet of the dangers that threatens us.

1) I confirm that it is not the concentration of the CO2 in the atmosphere that produces the warming up and therefore the end of life on our planet.

2) ) it is not the Carbon tax imposed by the governments, that are going to decrease the concentration of the CO2 in the atmosphere, since they impose a tax but continue to emit greenhouse gases.

The most powerful countries even propose to purchase the so-called CO2 quotas of the poorest countries. In fact, they propose the poor countries to compromise their possible development against their misery.

It is as to propose a poor to sell his kidney to subsist.

Besides all gases are to greenhouse effect. Even the O2, the N2, etc. are also greenhouse Gases. They only defer by their coefficient calorific Cv.

3) The real danger doesn't come certainly from the CO2 that the poorest countries reject timidly but comes of the lies (greenhouse effect…) of the most powerful to slow down the poorest conties development , it comes from :

- The absurd policies that succeed to the famine for the populations of the poor countries

- The wars sustained by the most powerful against the poorest

- The weapons that the most powerful possess and that they don't hesitate to use them against those that don't have them.

- ….

The real danger doesn't come certainly from the CO2 that the poorest countries reject timidly but comes from the lies (greenhouse effect …) of the most powerful to slow down the development of the poorest.

I tend to agree with Martin, although I'm no physicist. I had also read about this and other experiments. However, the existence of the greenhouse effect alone is not sufficient to establish (1) that doubling CO2 will increase global temperatures by around 3° (between 1.5° and 4.5°); this require strong positive feedbacks; nor it suffices to establish (2) that it is "very likely" that "most" of the recent warming is attributable to increases in CO2 (this would require discarding other influences, ranging from changes in solar activity to multidecadal intensification cycles of ENSO or in the Pacific Decadal Oscillation, among other possibilities).

Martin, thanks for your comment. Besides my interest in the work you cite, let me say that I do not consider that some physical proposition could be "proved" by the use of a model or an ensemble of models. I understood we were talking about "reality tests". One does not prove facts with models: one proves models with facts.

Martin, thanks for the references. I am familiar with uncertainty issues regarding climate modelling, but my remark was of wider import, focusing rather on the more general issue of how you provide grounds for scientific propositions. You use models to formulate the propositions, and many details in the models have theoretical and empirical basis, but the fact that you have been able to build a model and to formulate a prediction using that model is not equivalent to providing a proof of the truth of your empirical prediction (for that you'd need observation, and this lies many years ahead in the future), and even less so does it provide a proof that your model provides a correct picture (or THE correct picture) of the causal chains underlying the phenomenon in question.

We know since Duhem and Popper, who wrote respectively 98 and 76 years ago, that usually many possible models or theories could account for the same set of phenomena, but this does not make them "true". Popper thought the most you can aspire to is refuting the theory or model (if it is contradicted by facts). Duhem (and later Lakatos and others) suggested that even refutation is not easily achieved, since many "refuted" theories or models can be adjusted ex post and ad hoc (e.g. modifying some auxiliary hypothesis) to explain away or accommodate any empirical anomaly that appears to "refute" the theory.

This is particularly applicable in the case of projections of future events, and most especially for complex or chaotic systems such as the Earth climate. As one American President famously said, "predictions are hard, especially about the future".

For the record, I may have my doubts but do not pretend any authority in the matter of deciding on the magnitude and causes of climate change. In fact, my recent book on the impact of climate change on agriculture and food security uses the IPCC climate projections, not questioning their validity (although I did question certain aspects of the demographic and economic assumptions in the story lines of some AR4 scenarios). The present discussion was elicited by the original question whether climate change is natural or man-made (or both, one should add), and my intervention was limited to pointing out uncertainties and objections posed by various scientists that remain skeptical or unconvinced about specific technical details of those climate projections.

Reference to the alluded book is in the Publications section of my Researchgate profile, and the book can be found at Amazon.com. Purchase orders are welcome.

Martin, even when making projections based on scenarios, one is always doing a "prediction" in the scientific sense of the word, like "predicting" that hitting an egg with a hammer will crush the egg. If your model is somewhat flawed, perhaps the egg survives. Or more to the point, perhaps your projection of what would happen with the climate under such and such level of emissions turns out to be wrong, if (IF) for some unaccountable reason attributable to human fallibility some parameter of the model (say, the level of cloudiness and role to be played by clouds in a world with more CO2) turns out to be off the mark. Which is after all a possibility to be entertained, is it not?

Martin Wattenbach

The experience cited :

http://www.espere.net/Unitedkingdom/water/uk_watexpgreenhouse.htm

don't prove the greenhouse effect that would be responsible for the climatic warming up.

I - CONDITIONS OF THE EXPERIENCE

1) the experience is in an confined space (volume = constant): (C1 the left hand side glass vessel is filled with pure carbon dioxide, C2 the right hand side vessel is filled with normal air containing only about 0,037% of carbon dioxide) doesn't correspond at all to an opened space as the earth and the space.

2) The experience is made at the temperature of the laboratory (30 °C).

II - This experience proves that:

1) For the same temperature T, the specific heat Cp of the CO2 is bigger than the specific heat Cp of air.

No one needs to demonstrate this, since the values of Cp are known since a very long time :

CO2 in T = 30 °C: Cp = 36.4 103 J / kg K T at = -30 °C: Cp = 1.97 103 J / kg K

http://www.engineeringtoolbox.com/carbon-dioxide-d_1000.html

Air in T = 40 °C: Cp = 1.005 103 J / kg K T at = -50 °C: Cp = 1.005 103 J / kg K

http://www.engineeringtoolbox.com/air-properties-d_156.html

It is normal that the temperature of a quantity of CO2 confined in a volume, is bigger than the temperature of the same quantity of air confined in the same volume if they receive the same quantity of energy.

2) If it was not the case, then the air that we breathe, warms up very quickly and go up therefore, and we will be asphyxiated, for lack of air.

The CO2 heats very quickly (Cp = 36.4 103 J / kg K to 30 °C) and bring up, what purifies the air of the earth ground (eliminate the excess of CO2 and of all toxic gases).

3) when the CO2 warms up (at the earth ground), it goes up in the atmosphere, to get cold, and its Cp specific heat decreases (Cp = 1.97 103 J / kg K at -30 °C). Whereas the Cp of air remains nearly constant according to the temperature. Air remains glued to the earth ground. It doesn't leave the surface of the earth very easily whereas the CO2 warms up more quickly and leave the earth ground. It is in the high atmosphere that the CO2 prefers to remain. And if it warms, it climbs even higher to free itself of its heat.

Conclusion:

This experience proves what everybody knows.

Can one wonder that the temperature of a piece of copper exposed to the sun is bigger than the temperature of a piece of wood?

III. THE SECOND LAW OF THE THERMODYNAMICS

A cold body cannot heat a body that is hotter than it. It is the hot body that heats the body that is colder than it.

1) When CO2 gas heats, it goes up. The temperatures there are -30 °C to -40 °C. mean temperature of the earth ground is of +15 °C. How does a body at -40 °C (CO2 of the atmosphere) to heat a body at +15 (earth ground)?

2) The heat transfer is toward the lowest temperatures.

IV. Greenhouse effect

1) Of what greenhouse effect does one speak?

- The greenhouse effect of the gardeners and cars in parking (exposed to the sun)?

(Confined space, Transfer of heat by contact and by convection)

- Greenhouse effect of the IPCC?

(Opened space and transfer of Heat by radiations)

2) Old Arrhenius

Arrhenius tried to explain the greenhouse effect of the gardeners. I affirm that he was mistaken.

Arrhenius thought that the gardener's greenhouse warmed up because the glasses of the greenhouse absorb radiations emitted by the soil of the greenhouse and re-emit the IR radiations that warm the greenhouse. It is the greenhouse effect of the IPCC. It is false.

The greenhouse warms up because air is confined in the volume of the greenhouse. Air warms up by contact with soil, and the convection makes so that all the air of the greenhouse warms up. If the greenhouse is open, the hot air leaves the greenhouse.

3) Old Arrhenius is not the good reference in this case.

The partisans of the greenhouse effect of the IPCC lack arguments!

Probably both. Definitely both.

But one important thing is that, independent of the reason for warming, the ice still melts above 0 C.

So unless we want our grandchildren to fight over land and food (and by "fight" I do not mean spirited discussion), we need to work on reducing/mitigating/anticipating the warming just for this single reason, out of many.

There is some probability that natural global cooling will take care of it some day, but it is like a severe increasing pain in the right low abdomen: there is some probability that it is not Appendicitis, but who would be waiting to go to doctor ASAP?

Nice discussions on the climate change. The technicalities in the discussions make it more interesting. The questions then is, is there something we can do to reduce the impact? If we do accept that humans 'also' contribute to the problem then we have to look at mitigating and adaptation procedures otherwise our children and their children are in for trouble.

Martin

The experience in the web :

http://www.youtube.com/watch?v=AvpenpBXAmM

shows that the CO2 is heavier than air, it is normal since the density of the CO2 is bigger than the one of air :

http://www.engineeringtoolbox.com/gas-density-d_158.html.

For Arrhenius work, see :

http://arxiv.org/pdf/0707.1161v4.pdf

Dear all,

This is a great discussion that you have about the scientific focus of climate change. My knownledge about GHG emissions shows that this is a fundamental factor to increase of world temperature, but all the scientific discussion about it shows that there are many implications and different points of view, wich means that more research must be done on this area. Anyway this is a fact that climate change is happening, I live in a tropical country and I can feel the changes happening every year and I know that it´s happening in everywhere in the world, so this is important to have disucussions like this and try and make what we can do to help the world´s climate stop its change and consequently stop the disasters caused by the current condition.

Best regards to all,

Luciana

Dear Luciana Andrade

The climatic changes are a reality. It's a good thing it is thus.

It's a good thing there are the fall, the winters, the spring and the summer. Do you agree? These are climatic changes of period one year.

Think about other climatic changes, climatic changes of bigger periods. These are the Great Seasons Climatic.

See :

1) A. Boucenna, The Great Season Climatic Oscillation,International Review of PHYSICS 1(2007) 53-55.

http://arxiv.org/ftp/physics/papers/0701/0701283.pdf

2) A. Boucenna, The Great Season Climatic Oscillation and the Global Warming,

Global Conference On Global Warming, July 6-10, 2008, Istanbul, Turkey.

http://arxiv.org/ftp/arxiv/papers/0808/0808.0897.pdf

Best regards

Es muss unterschieden werden zwischen Umweltverschmutzung und Klimawandel!

1-Umweltverschmutzung ist Menschenswerk!

2-Klimawandel ist ein Prozess das vom Anfangstag des universums angefangen hat und bis Ende des Universums laufen wird!

3- Klimawandel ist resultiert durch die enge Beziehung zwischen Sonne und Erde!

4- Sonne war grosser waermer und entfernter von uns! Allmaehlich ward sie kuehler , kleiner und naeher zu uns!

5- Das machte die Tage und naechte kurzer und kurzer.

6- There Erste Tag war there laengste Tag I'm Leben des Universum, unser tag ist there kurzeste und die kommende Tage werden kurzer und kurzer.

7- Geologen und Archaeologen mussen das schon laengst verstanden haben!

8- Wir erleben weniger Kuhlung dass Minimum Pol temperatur hoch gen Null geht!

9- Alexandria von Kleopatra liegt schon 25 m unter Wasser oder noch mehr!

https://sites.google.com/site/jamousiyah/

One must distinguish between pollution and climate change!

1 - pollution is man's work!

2 - Climate change is a process from the initial day of the universe has begun and will run until the end of the universe!

3 - Climate change is the result of the close relationship between the sun and the earth!

4 - large sun was warmer and more distant from us! Gradually it became cooler, smaller and closer to us!

5 - It made the days and nights shorter and shorter.

6 - There first day was there longest days I'm the life of the universe, our day is shortest and the coming days there will be short and brief.

7 - geologists and archaeologists must have understood long ago!

8 - We are seeing less COOLING minimum pole that goes up towards zero temperatures!

9 - Alexandria by Cleopatra is already 25 meters under water, or even more!

https://sites.google.com/site/jamousiyah/

8 - We are seeing less COOLING , that Minimum pole temperature goes up towards zero temperatures!

Hi all,

I read a few opinions here, and with most of it, I agree. Combination of human activities and natural factors is very close to the reason of ongoing climate changes. Cclimate is not stabile, solid for sure not fragile. it is an living phenomena, complex of not well understandable factors, parameters and doings.

For example, this winter in Western Balkan, was one of the coldest in last few decades. Even T increseas in last week, still deep snow is everywhere. Could we expect next winter the same? I dont know that anybody ahalf a year ago spoke about cold winter? Just old people? And you know how they predicted it?

Acorn crop very well. All oak forests were more than rich with acorn. So the nature thought about wild boars. More before, we talk about it? Wild boras and other animals in this chain.

We need to keep nature. And learn thoise which do not respect nature, to respect it. Zhis is the clue. At least I thinks so :)!

From Said Jamous: "Alexandria by Cleopatra is already 25 meters under water, or even more!!".

Of course this is true, but it is not a result of rising sea level. The seas have not risen 25 metres in the latest 2000 years. Some elementary notions:

1. The effects of global warming on sea level refer to the eustatic sea level, which reflects the amount of water in the sea, and may be indicated by the average altitude of the sea surface (although not exactly).

2. The relative level of the sea (relative to some land surface or some object on the land surface, such as Alexandria) is the result of several simultaneous processes:

a. Increase or decrease in eustatic sea level

b. Emergence or subsidence of land substrate (due to tectonics or other processes).

c. Deposition of land sediment on the coast (e.g. at the mouth of rivers) partially or totally offset by movement of sediment from land to the sea (carried by tidal force and water movement).

d. Differences in water level at different parts of the globe: higher near the Polar Circles, minimum near the Equator, the difference being +/- 15 cm.

e. Differences of sea level at different parts of the sea due to oceanic currents and other processes, +/- 5 cm.

Examples:

- Land in Northern latitudes, such as Scandinavia, is still "rebounding" from the low level forced on it by the pressure of the ice deposited on top of it during the last Glacial Age (which ended some 12000 years ago). Thus coastal land in Norway or Sweden surges a few millimeters per year. This process, by itself, causes the local sea level to decrease (other factors may cause it to rise, and the net effects depends on the specific place considered).

- Land in some great deltas is increasing in extent and height due to large deposition of sediment, e.g. in the Ganges Delta which makes most of the Bangladesh territory. The drift of sediment into the sea, at the moment, does not offset the arrival of new sediment. As a result, the extent of land in Bangladesh lowlands, and its elevation over sea level, is actually increasing. (There was much fear that rising sea level due to climate change would inundate Bangladesh, but it is not happening yet).

- Differences of sea level by latitude, up to 15 cm, can be seen illustrated in the 2007 IPCC report, Working Group I, figure 5.23 and surrounding text, pp.420.421, Figure at http://www.ipcc.ch/graphics/ar4-wg1/jpg/fig-5-23.jpg.

-Differences of sea level at various points of the sea and the coasts, +/- 5cm, can be seen illustrated in the same report, figure 10.32 at p.813. Figure available at http://www.ipcc.ch/graphics/ar4-wg1/jpg/fig-10-32.jpg.

I do not know the specific causes why Alexandria sunk, but other low-lying coastal sites of the Ancient world did not suffer the same fate in the latest 2000 years (e.g. the port of Marseille in Southern France, or the city of Rome built over marshes at sea level and at a short distance from the sea, or the Roman port of Ostia at the mouth of the Tiber river some few miles from Rome, among many other examples). Alexandria is under water, but not because of the rise in eustatic sea level.

Climate changes was happening before humans were here and it will always going to happen, its is not a problem, its just as it is. When people talk about climate change nowadays, they are actually talking about a lifetime perceptible increase of temperature, a visible change in a very short time period when compared to geological time scale of the glacial cycles. In the other hand, philosophically speaking, I would like to raise a question: Once human been is an Earth's natural developed organism, isn't the human influence also a natural event?

It is not Alexandria only !

1- Gaza in Palestine : old city is in the west under Water

2- Venice : The huge buildings of the Huge Venice are under Water ! They are the base for the Buildings you see

3- on western continental shelf of Africa under water are very huge buildings are seen by google esrth !

4- there are many lime caves with stalactites which can only occur in mountains are found now under water in all continents !

Lets remmember that Global Warming and the Ozone Depletion Phenomenon are different things. In fact I would like to bring to this discussion the very results that our group found out that became my own PhD thesis. We observed a possible relation between the east Antarctica cooling and the ozone depletion.

Indeed, Mohammad, we are talking about the anthropogenic impact on the O3 layer as it is known since the last 40 years. Our data, retrieved from an shallow Ice core on 80o South show a possible influence of the human caused O3 depletion on central antarctica cooling. It rases a big inssue when we think about one human impact minimising the effects of annother human impact.

I will try to express an idea very common in Brazil, but I'm not sure is worldwide understandable: who came first: egg or chicken? The same for CO2 in atmosphere: Is the increasing CO2 by human activities causing global warming or natural global warming is increasing the CO2 concentration? Let's think more in logical processes and less in statistical data. Is there any stable isotope expert between us to share the knowledge about C3 and C4 (warm and cold regions)?

Helio,

along geological history it appears that changes in temperature PRECEDED increases in CO2 (by several hundred years). However, increasing CO2 causes in turn a greenhouse effect that, by itself, warms the planet, although it may be exacerbated or dampened by positive or negative feedbacks.

So warming causes CO2, and CO2 (at least by itself, not counting feedbacks) causes more warming. These two effects, if both are present, would reinforce each other causing a positive loop of warming of indefinite duration This has clearly not happened in the past, thus some powerful negative feedbacks must be present or we would be boiling hot by now.

As you imply, much of the recent estimates about the causal chain leading from fossil fuels to greenhouse gasses to global warming are based on correlating recent increases in CO2 with recent increases in warming, especially in the latter third of the 20th century, but many other influences are present and are difficult to control for.

It is true that "97% of scientists" agree that the world has been warming recently, and probably 100% agree that CO2 by itself causes warming. But the doubtful devil is in the details. The consensus on feedbacks and other "details" is much less firm.

Not that science can be settled by "consensus": science is never "settled" (new questions arise all the time), and the persistence or demise of theories depend not on consensus (which is a consequence) but on the emergence of new evidence and better theories. Many times in history a scientific consensus was shaken or superseded by new knowledge (Copernicus, Newton, Einstein, to name just a few, but also many more in specific fields: cf the recent Nobel Prize on quasi-crystals, awarded to the lone scientist that insisted they exist to the derision of all the rest, who thought he was crazy).

No doubt about global warming, only about the reasons. I agree that devil's in the details. Maybe that's why some explanations are so doubtful. Atmospheric temperature, I think, is a so complex process that, for me, does not make sense that only human contribution causes that much.

Climate change is a natural process, human activities are actually hastening it I guess...

@Original Post of Luciana Andrade

My favourite attribution study is Combinations of Natural and Anthropogenic Forcings in Twentieth-Century Climate, Meehl et al. Journal of Climate (2004). http://cawcr.gov.au/bmrc/clfor/cfstaff/jma/meehl_additivity.pdf

It shows that the current warming is anthropogenic, and without anthropogenic forcing, we would be seeing a slight cooling instead. But it's my favourite because the finding of additivity is very cool. I'm sure there's been some improvement to models in the intervening 8 years.

Dr. Naomi Oreskes did a literature review for the decade 1993 to 2003, using papers that were indexed by the ISI, with the keywords "Global Climate Change" (not "Climate Change" as it appeared in her essay published in Science). She looked at which of the papers attributed most of the warming since 1950 to anthropogenic forcing, on the balance of probability. The results were quite one-sided.

"The 928 papers were divided into six categories: explicit endorsement of the consensus position, evaluation of impacts, mitigation proposals, methods, paleoclimate analysis, and rejection of the consensus position. Of all the papers, 75% fell into the first three categories, either explicitly or implicitly accepting the consensus view; 25% dealt with methods or paleoclimate, taking no position on current anthropogenic climate change. Remarkably, none of the papers disagreed with the consensus position." - ( http://www.sciencemag.org/content/306/5702/1686.full )

@Hector Maletta

Re: "However, increasing CO2 causes in turn a greenhouse effect that, by itself, warms the planet, although it may be exacerbated or dampened by positive or negative feedbacks.

So warming causes CO2, and CO2 (at least by itself, not counting feedbacks) causes more warming. These two effects, if both are present, would reinforce each other causing a positive loop of warming of indefinite duration"

As the world warms, it's blackbody radiation increases, until a balance is reached, and the warming stops. The warming is not of indefinite duration, it's merely runaway for a period.

And the end of the interglacials of the holocene do show this. It takes 100,000 years for the temperature to wander it's way down (not monotonically, down nevertheless) to the bottom of the glaciation period, but that is followed by a sudden (monotonic) rise of 10-12 K all in 5000 or 6000 years.

( http://www.nature.com/nature/journal/v453/n7193/images/nature06949-f2.2.jpg ) from High-resolution carbon dioxide concentration record 650,000-800,000 years before present , Lüthi et al, Nature (2008)

Climate change is related to both the natural and anthropogenic causes as said by the other persons also.The main natural cause is earth's natural axis and orbit in rerlation to sun.And the main kulprit is human.Human intervention in all natural proceeses are the leading cause of climate change.So major thrust should be given to reduce the anthropogenic causes which contributes for climate change.

climate change occurring naturally is normal and tolerable. But, the human society disturbing the climate in unwanted manner. This type of climate change caused by human activities are unpredictable.

Both, the human accelerates the heating process, however own the planet goes through cycles of heating and cooling, these cycles may vary in amplitude occurring among scales in decades.

Henrique, it appears that doubling the CO2 atmospheric concentration would increase global temperature by about 1°C. This seems beyond doubt (though one never knows: see below). The total effect is that 1°C plus the net effect of (positive and negative) feedbacks, such as increased water vapor and reduced albedo (positive) or increased clouds (negative). The main issue is the sign and size of the net feedbacks, especially because clouds are not well understood and poorly modeled. IPCC models presume an average sensitivity (with feedbacks) of 3°C per doubling of CO2 concentration (with uncertainties going from 1.5° to 4.5°) but these estimates are based on a very incomplete assessment of the proportion of new water vapor (from more evaporation caused by CO2 through that 1°C warming) that would go into clouds, and also some very cursory assessment of the cooling effect of aerosols released (along with CO2) when burning fossil fuels, among other issues.

Researchers engaged directly in climate modeling support the 3° estimate, but other physicists vary in their opinion, and the matter is indeed under debate. Of course, those estimates are an INPUT into the models, not a RESULT proved by the models (models of this kind cannot prove an empirical proposition).

In this matter, one should not be distracted by the idea that one opinion or the other is in the majority: science progresses because alternative hypotheses compete with each other, and it is often the case that a prevailing consensus is gradually or abruptly overthrown. Until the unknown and amateurish patent clerk Albert Einstein published his papers in 1905, practically 100% of physicists thought that time and space were absolute and unrelated, but their unanimous agreement did not make them right.

Similar episodes (albeit of smaller repercussion) occur all the time in science. See for instance two recent Nobel prizes for discoveries that were consigned to derision for years, such as Barry Marshall's research conclusion that ulcers were caused by the Helicobacter coli bacterium, a result obtained in 1982 that was long derided as nonsense until finally accepted (Marshall received the 2005 Nobel prize in Physiology for his contribution); or Dan Schechtman's discovery of quasi-crystals (he made the discovery and formulated the theory in 1982, but was duly ostracized and ridiculed as a crank by the vast majority of his colleagues, until awarded the 2011 Nobel prize in Chemistry precisely for that discovery).

As I said before. I think both. There are several changes in different scale that we need to consider. We are talking about very 5 years, every 100 or 1000 years…... Every thing changes The movement of the earth, for example, will change the climate due to the distribution of the sun light and so on There were always climate changes and there will be other climates changes in the future. The difference is that now a day we have more instruments, Internet, better researches, more human capacity (should be more specialist) and I am not talking just by the equipment, but the opportunities that we have to exchange information around the world. It allows us to know what happen and also allow us to establish relations among different factors, different situation. In the past we just consider any event “like ours” but now we know that are more complex, we must think more about that.

And off course human activities, also contribute to the climate changes, reduce the mountain, burn forest, use some chemicals that are not healthy to the nature and so on.

What we must do?.. We are scientific, we must prepare regional program, and publish results, we must contribute to reduce the “bad effects” of the industry process, work with the private industry, no just study the effects o just to said “they are destroying the environment and producing changes in the climate”. We must work in prevention with then, together. Is also impossible to stop the evolution of the industry, but we can work with them, using our scientific knowledge.

Thank you for your vision, Hector. We should eliminate the scientific dogmatism. That is what slows docmatismo knowledge, is the one who handles some scientific journals ...

True, the climate change must be viewed in the proper scale, it is also true, to be thought with the right standard. The atmosphere acts as a vector in which many variables at once. Most of them have magnitudes of energy that fluctuate temporally (day / night - winter / summer, etc.). That's why the climate should not be viewed as an entity that varies linearly, but has a pulse regimen.

Then, there are recurring pulses daily, seasonal, interannual, and even of centuries, millennia.

This lets you see the importance of possible scenarios of variability,

I think ...

Nobody is talking about Ocean Acidification. Probably THE biggest environmental issue we are facing, and we can do nothing about it! For years we thought that the ocean's ability to absorb CO2 through algae, etc, was a boon. It turns out, it may kill our ocean food webs by dissolving shell bearing critter's shells while they are forming... That is the base of the food web being melted...

Scott, to be precise, acidity is measured through the Ph scale, where a value of 7 is "neutral". Less than 7 is "acid", more than 7 is "base" or "alkaline". The oceans are alkaline. Absorption of carbon would reduce the alkalinicity of oceans, but it would not turn them into "acid": it would rather make them "less alkaline" or "more neutral" (pure water is neutral). Of course, the level of alkalinicity of oceans vary with location, but nowhere in the world it is near a state of "neutrality", let alone "acidity", nor is it expected to be any time soon.

In my opinion climate changes have happened for millions of years, are happening and will happen naturally and for millions of years with or without human society, in one or more spaces and different times in our globe. These climatic changes have passed, pass and will pass by one or more chaotic natural phenomena or not supported by this humane society of our globe. We, every day, step by step out, and with short-term, medium-term and long- term objectives should be more responsible and reasonable in thought, designed and operated with concrete measures against them.

@Hector Maletta - I beg to differ. See below.

The chemical process of ocean acidification

There is a constant exchange between the upper layers of the oceans and the atmosphere. Nature strives towards equilibrium, and thus for the ocean and the atmosphere to contain equal concentrations of CO2. Carbon dioxide in the atmosphere therefore dissolves in the surfacewaters of the oceans in order to establish a concentration inequilibrium with that of the atmosphere. As CO2 dissolves in the ocean it generates dramatic changes in sea water chemistry. CO2 reacts with water molecules (H2O) and forms the weak acid H2CO3 (carbonic acid). Most of this acid dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-). The increase in H+ ions reduces pH (measure of acidity) and the oceans acidify, that is they become more acidic or rather less alkaline since although the ocean is acidifying, its pH is still greater than 7 (that of water with a neutral pH). The average pH of today's surface waters is 8.1, which is approximately 0.1 pH units less than the estimated pre-industrial value 200 years ago (2,3).

Projections of future changes

Modeling demonstrates that if CO2 continues to be released on current trends, ocean average pH will reach 7.8 by the end of this century, corresponding to 0.5 units below the pre-industrial level, a pH level that has not been experienced for several millions of years (1). A change of 0.5 units might not sound as a very big change, but the pH scale is logaritmic meaning that such achange is equivalent to a three fold increase in H+ concentration. All this is happening at a speed 100 times greater than has ever been observed during the geological past. Several marine species, communities and ecosystems might not have the time to acclimate or adapt to these fast changes in ocean chemistry.

Possible consequences on marine organisms

The dissolution of carbon dioxide in sea water not only provokes an increase in hydrogen ions and thus a decline in pH, but also a decreasein a very important form of inorganic carbon: the carbonate ion (CO32-). Numerous marine organisms such as corals, mollusks, crustaceans and seaurchins rely on carbonate ions to form their calcareous shells or skeletons in a process known as calcification. The concentration of carbonate ions in the ocean largely determines whether there is dissolution or precipitation of aragonite and calcite, the two natural polymorphs of calcium carbonate (CaCO3), secreted in the form of shells or skeletons by these organisms. Today, surface waters are super saturated with respect to aragonite and calcite, meaning that carbonate ions are abundant. This super saturation is essential, not only for calcifying organisms to produce their skeletons or shells, but also to keep these structures intact. Existing shells and skeletons might dissolve if pH reach lower values, and the oceans turn corrosive for these organisms. Consequently, the results ofthe decrease in carbonate ions might be catastrophic for calcifying organisms which play an important role in the food chain and form diverse habitats helping the maintenance of biodiversity.

The magnitude of ocean acidification can be predicted with a high level of confidence since the ocean chemistry is well known. But the impacts of the acidification on marine organisms and their ecosystems is much less predictable. Not only calcifying organisms are potentially affected by ocean acidification. Other main physiological processes such as reproduction, growth and photosynthesis are susceptible to be impacted, possibly resulting in an important loss in marine biodiversity. But it is also possible that some species, like seagrasses that uses CO2 for photosynthesis, are positively influenced by ocean acidification. Ocean acidification research is still in its infancy and more studies are required to answer the numerous questions related to its biological and biogeochemical consequences.

References:

1) Caldeira, K., Wickett, M.E., 2003. Anthropogenic carbon and ocean pH. Nature 425 (6956): 365–365.

2) Key, R.M.; Kozyr, A.; Sabine, C.L.; Lee, K.; Wanninkhof, R.; Bullister, J.; Feely, R.A.; Millero, F.; Mordy, C. and Peng, T.-H. (2004). "A global ocean carbon climatology: Results from GLODAP". Global Biogeochemical Cycles 18

3) Orr J. C., Fabry V. J., Aumont O., Bopp L., Doney S. C., Feely R. A. et al. 2005. "Anthropogenic ocean acidification over the twenty-first century and its impact oncalcifying organisms". Nature 437 (7059): 681–686.

4) Raven, J. A. et al. 2005. Ocean acidification due to increasing atmospheric carbon dioxide. Royal Society, London, UK.

5) Sabine C. L. et al., 2004. The oceanic sink for anthropogenic CO2. Science 305:367-371.

6) Martin S. et al. 2008. Ocean acidification and its consequences. French ESSP Newsletter 21: 5-16.

7) IPCC 2007. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Summary for Policymakers.

@Scott,

thanks for the learned explanation, quite useful for a non specialist like me.

Just two short remarks:

1. The change in pH (-0.1 units, from preindustrial level of 8.2 to current 8.1) would have been caused by an increase of CO2 from 275 to 390 ppm (+41%). The function linking CO2 atmospheric concentration to surfacewater pH is logarithmic, as you say. Now, on a logarithmic function, this implies that doubling preindustrial CO2 to 550 ppm would decrease pH by nearly 0.2 pH units. Tripling the preindustrial level to 825 ppm would cause a decrease of about 0.3 units, and quadrupling to 1100 would cause a total pH change of 0.4 units approximately. By the same token, a logarithmic function of this kind would require 1650 ppm to cause a decrease of 0.5 units in oceanic pH.

Perhaps the function is not a simple log function, but I am following your lead in this. However, 1650 ppm is not projected in any IPCC model. Some rather extreme IPCC models go as far as projecting a CO2 concentration of about 1550 ppm, and none goes beyond that, but they only go that far in their projections under very unlikely assumptions about future population (growing wildly, as in scenario A2, totally against current projections and reaching 1250 ppm) or about energy sources (intensified fossil fuel use as in scenario A1F1, reaching 1550 ppm) or about technological change (no major breakthrough for 100 years in the field of energy generation, as assumed in all scenarios). Even under these rather far-fetched assumptions it seems a bit extreme to assume a decrease of pH by 0.5 units, which would require one to assume that CO2 concentrations would increase five-fold or more, relative to preindustrial levels, which is not assumed even in the most extreme IPCC climate change models. One has to select specifically the most extreme among all scenarios and their variants (namely A1F1, the "worst" scenario in the A1 family) to find anything that resembles your estimate, and even that worst case falls short of requirements, but nonetheless you say that level of concentration (and its effects on sea life) "will" happen. I tend to be more prudent in these matters, but this is me.

2. "Modeling demonstrates", you say. I would rather suggest that model projections do not "demonstrate" or "prove" anything. They just show the implications of some initial assumptions. Note first that such models do not produce falsifiable "predictions", but only "projections" under a certain imaginary "scenario" of what would happen in the future. Projections are not empirically falsifiable. Those projections, besides, are not only scenario-dependent, but also model-dependent and even model-run-dependent. Most models use heavy parameterization, and projections often vary widely from model to model, or after small changes in model parameters, even under the same imaginary "scenario". Moreover, as the IPCC itself says, even if a model is good at planetary level, regional projections are only very rough guesses. What would actually happen, under a given scenario and model, in some specific area such as the Fiji Islands or the Bay of Biscayne (let alone a specific location in those areas) is basically guessing.

I suppose models is not all. Experiments in this matter (effects of pH on marine life) are feasible, as organisms can be put in marine water with various levels of pH to observe the results empirically. In experiments concerning organisms that reproduce relatively fast, one is not restricted to first order impacts: one may also measure natural selection at work, as some individuals or varieties of those organisms thrive better in each pH-level environment. If (underline IF) a significant change in pH occurs as a result of CO2 emissions, it may be the case that some organisms now thriving in, say, the Australian coral reef or the Caribbean would suffer a selective pressure, and as a result some varieties may disappear in each particular location while other varieties survive (and even the former varieties may start prospering elsewhere).

I do not know whether such experiments exist, for how long have they been running, and what are the results. Besides experiments, I have also read that seawater pH vary with location, especially near the coast, which bears on the kinds of organisms thriving in each location; and thus some observational study about which species and varieties thrive under varying levels of alkalinicity would be also useful, even if admittedly lacking some of the advantages of a randomized long-running experiment. From an epistemological viewpoint, the general thrust of this second remark is that models may suggest hypotheses, but only experiments and systematic empirical observation can actually test such hypotheses.

Just the idle thoughts of one not very knowledgeable in marine science, of course.

@Henrique Kugler

re: "1. Looking back to the past million years, we see there´s nothing unusual about the climate patterns of the 20th centrury, right?"

I think that they are somewhat unusual. Looking at the CO2 and temperature of the past 1 million years, there seems to be some periodicity to the timing of the interglacial periods. And given that we passed the climatic optimum about 7k years ago, a further warming period, such as the 20th century is not previously observed.

The current rate of warming is very fast too. It's difficult to resolve warming this fast from most climate proxies, and certainly from ice cores, although they do leave evidence of a very rapid change having happened. I think that its fair to say that warming this fast is certainly rare.

re:"2. Again, why the heck is CO2 being considered the bad guy, being it almost neglectable in the overall atmospheric composition?"

Because it is the warming effect, not the proportion of atmospheric content that is important for climate change.

The increase in CO2 since pre-industrial times is applying about 1.7 W/m2 to the earth. It's the single largest source of radiative forcing cause the current climate change. Being the largest cause of climate change it is considered the main bad guy.

re:"There is a quite interesting article here: http://arxiv.org/abs/1201.1301 "

Scarfetta has half a dozen or more papers where he proposes that climate change is partly due to the orbits of Jupiter and Saturn. It's interesting enough as a mathematical exercise, but in terms of claiming that there might be some real or practical aspect to this, I'd be interested in some plausible physical mechanism.

We know that greenhouse gasses cause a greenhouse effect, and we know how. Explanations of earth's climate change that propose completely unknown mechanisms have a lot of work to do before being able to be taken seriously in any context outside theoretical curve-fitting.

While it is obviously a broad term meaning geologically slow ann not so slow changes due to Earth's relation to the Sun, Archer, in the Long Thaw is your best source on why this question may miss the point. Recent levels of carbon dioxide in the atmosphere, the rate at which the increase is being recorded and the isotopic ratios we see suggest that combustion is perturbing an underlying trend. Wallace S. Broecker, some years ago tried to test the notion that this was a natural shift.

http://www.earth.columbia.edu/articles/view/2246

To my mind the isotopes do not deceive us as to the causes, the heavier carbon isotopes are the product of combustion, high energy combustion leaves behind a fingerprint, if you will allow the metaphor. There is also a good article by Camille Parmesan warning about attribution when discussing climate (rapid warming or cooling) associated causes for what we describe in biological changes. ["Overstretching attribution" Nature Climate Change, vol 1, April 2011, Macmillan, pp. 2-4,] notes "regardless of the causes of the climate events or trends." (p.3)

That brings me to the point of arguing that asking what the causes of this rapid accumulation carbon dioxide levels in the atmosphere and ocean pH changes misses the point. Adaptation is so critical for most of the world's populations located in marginal arid or marginal coastal lands that arguing over combustion robs us of valuable research time to consider what sorts of adaptive responses work better than other responses to altered snow and rain patterns. Mitigating our waste of resources for whatever reason is of course equally important. By that I mean coal and oil require a good deal of water. Do we have reliable sources of water to keep generating electricity from water intensive sources?

In conclusion, combustion is exacerbating the thermal capacity of the planet to redistribute the infra-red radiation without unexpected shifts that harm natural and human systems. Never have civilizations developed with this high a level of carbon dioxide in the atmosphere rising at such a rapid rate.

Some of the books I read recently reveal the fact that climate change has undergone large fluctuations over the history of the earth without the influence of any human activities. As for instance, there was no ice or snow at either the North or South pole during the age of dinosaurs due to the climate which was warmer than today about 100 million years ago.

Moreover, much of North America was covered by ice sheets which is said to be thousands of feet thick because it was much colder than today some 20,000 years before. Human activities did not play any role in these climate fluctuations. But over the few centuries, it is said that human activities have expanded to the point that they can significantly influence many global-scale processes, so they must be considered a potential cause of the observed global warming.

@ Henrique Kugler

I haven't read Prof. Shigenori Maruyama's book. I am generally more sceptical of literature that goes straight to the public rather than addressing the scientific community, but I cannot speak for this particular book.

re: "For now my main concern is the blind reliability on IPCC reports – being them somewhat politically driven."

I'm only familiar with the reports of working group I, and my (possibly mistaken - note that my field is mathematics, not climate science) opinion is that they do reference a good breadth of the literature. The IPCC process certainly does have two political review phases, which is two more than is usual for scientific publications. The consequences of that isn't generally a bias towards overstating either the findings of the science nor the confidence of those findings. A great failing of democratic systems is their resistance to enacting legislation that applies a cost during the current term, but whose benefits fall outside that term. And so naturally, strongly stated findings of climate science are unwelcome.

And the USA, China, Saudi Arabia and Russia are all vociferous during the political review phases, and have a clear agenda, because the production or consumption of fossil fuels is central to their economies.

re: "I'm not a specialist, but I tend not to rely on such models, knowing that they are unable to deal with the most important parameter responsible for climate balance: the water steam. I guess it's widely known that water steam (and clouds!) is by far the most important thermal regulator on Earth, right?"

Water vapour is the strongest greenhouse gas, and clouds are also very important but complicated. I wouldn't say that they regulate the Earth's temperature. Water vapour provides positive feedback to other warming, because warmer air increases both the rate of evapotranspiration and the capacity of the atmosphere to hold water-vapour. So it anti-regulates temperature.

On clouds, the jury is still out, but observational records (Observational and Model Evidence for Positive Low-Level Cloud Feedback, Clement et al, SCIENCE (2009) -http://www.realscience.org.uk/clement090724.pdf ) and radiation budget measurements (A determination of the cloud feedback from climate variations over the past decade, Dessler , SCIENCE (2010) http://geotest.tamu.edu/userfiles/216/dessler10b.pdf ), both imply a feedback that is at least not strongly negative - so they probably don't regulate much, if at all.

Opinion appears still divided on that last point. Climate science heavyweight Kevin Trenberth stepped in to the mud-slinging match subsequent to the Dessler paper above, and it seems to me that the analysis is mixed, but leaning towards the interpretation that cloud feedback is likely to be small, although this interpretation is vulnerable because of the shortness of a reliable data record. (Issues in Establishing Climate Sensitivity in Recent Studies, Trenberth et al REMOTE SENSING (2011), http://echorock.cgd.ucar.edu/cas/Trenberth/trenberth.papers/remotesensing-03-02051.pdf )

"Also the models can't parametrize astronomical influences (which are indeed of paramount importance when it comes to the input of energy that we receive on Earth). The Milankovitch cycle, for instance, is not even mentioned."

The Milankovitch cycles are paramount when analysing climate over a time period that is relevant to the length of the Milankovitch cycle ... about 100,000 years. (Or even a lot less if you focus on the end of a glaciation. The glaciation periods end suddenly with runaway warming that lifts the global mean surface temperature about 10°C in 5000 or 6000 years). But that warming ended 7000 years ago, and the effect of Milankovich cycles on the warming since the last half of last century is unimportant.

"To sum up, I think its too much of an insane generalization to say that CO2 and greenhouse gases alike are the bad guys of the plot – considering the unimaginable complexity of the whole climatological dynamics on Earth. Does that make any sense?"

I think that we're confident that the observed warming is CO2 warming. The shape of the warming in time and in space has the fingerprint of CO2 warming, and from our knowledge of sources of radiative forcing, CO2 forcing dominates the others compared to the start of the industrial revolution. I'm not aware of any question in the scientific discourse that the long lived greenhouse gasses are the culprit. There is a large uncertainty surrounding what the effect of that warming will be, once the system reaches the steady state, and this is where the mud-slinging is occurring. But central estimates are grim. Upper range estimates are horrible to contemplate.

Change is the only constant and over the years change is happening. In this context climate has always been changing. The change however had been at such a pace and on such a time scale that it was precisely difficult to figure out.

Moreover, the entire interplay of energy and matter is an area of extensive research. In above context it is really challenging to define the premises of climate change. However, the 200 years of industrial civilization has jeopardized the important natural cycles which are the key to the sustainability and endurance of the earth systems.

Whether climate change is happening can be a matter of debate but this without doubt we all know that we have really messed up with all the natural matter cycles from bio-geo-chemical cycles to the water cycle and eventually messed up with the entire energy budget of the earth system.

Since we (human industrial civilization) have messed up with these cycles we have to bear the consequences of the same. The current scenario in relation to climate change therefore require profound understanding of the linkages between different matter cycles and the impact of disturbing these natural cycles on the earth system.

Climatic changes are natural process and goes on due to one factor / species or the other....only worrying part is whether it is a long term process of stress which can be resisted initially and slowly adapted with ease or a short term drastic change that do not allow living beings time to adapt but force to succumb.......

presently some of human contribution factors (especially since last century) are leading to drastic changes ,which need to be controlled or eliminated

Robin Grant is particularly correct when she asserts that "The current rate of warming is very fast too. It's difficult to resolve warming this fast from most climate proxies, and certainly from ice cores, although they do leave evidence of a very rapid change having happened. I think that its fair to say that warming this fast is certainly rare."

Hence the correct logic of Dr.B.k Chakravarthy's comment · (INDIA) that the "only worrying part is whether it is a long term process of stress which can be resisted initially and slowly adapted with ease or a short term drastic change that do not allow living beings time to adapt" to what we have seen in the last fifty years. The rapid accelerating and prolonged impact of carbon dioxide levels in the atmosphere and the oceans is not something "natural" in origin, thought the impacts and the feedback responses to the abrupt increases are of course natural.

James Lovelock's recent book The Revenge of Gaia is a must read fro some of the persistent questions that arise in this context. What is most disturbing about the recent dumping of carbon dioxide into the air and oceans more quickly than these can be absorbed by natural systems is that people have been adversely impacted and between twenty to fifty million people displaced worldwide due to unprecedented flooding or prolonged and unrelenting droughts. Our insistence on using coal and oil has had widespread negative impacts on human lives and peoples' livelihoods.

Climate change is occurring naturally and it is also caused by the accumulation of man-made carbon dioxide (CO2) and other greenhouse gases in the atmosphere. The rate of accumulation depends on how much CO2 mankind emits and how much of this excess CO2 is absorbed by plants and soil or is transported down into the ocean depths by plankton (microscopic plants and animals). The oceans influence the climate by absorbing and storing carbon dioxide. Scientists believe that the oceans currently absorb 30-50% of the CO2 produced by the burning of fossil fuel. If they did not soak up any CO2, atmospheric CO2 levels would be much higher than the current level of 355 parts per million by volume (ppmv) - probably around 500-600 ppmv.

It is interesting to note that CO2 is still believed to be the No 1 greenhouse gas instead of water vapour. Many excellent climate scientist (e.g. Richard Lindzen, Roy Spencer, John Christy, etc) have dealt with the issue and shown both in books and research articles that CO2 is a very minor player governing global climate.

So what drives climate?

The answer must obviously be found in the hydrological cycle, where the oceans play a major role together with extraterrestrial process with the Sun having the ultimate role. We know that solar energy (insolation) does not vary sufficiently to explain the climatic excursion our planet has experienced on a short and long term. It is sufficient to consider the Little Ice Age and the Medieval Warm Period, not mentioning the past ice ages, to understand that there are many complicated factors to consider before we can explain climate variability.

Solar activity is naturally a major player but this does not mean only total solar insolation (TSI) but also solar magnetic activity. Also the gravitational influence of the entire solar system must be taken in account, not forgetting our own natural satellite, the Moon, influencing at least ocean tides. Very interesting views on climate variability and cosmic activity have been presented by Henrik Svensmark.

A very simplistic example how the water cycle could adjust climate is the following mental construct: The Sun warms the ocean surface increasing evaporation. Increase in water vapour content decreases the density of the air, which thus rises to higher altitudes where eventually adiabatic cooling reaches a level where water vapour starts to condense. The availability of condensation nuclei, possibly enhanced by high energy cosmic radiation especially during low level solar magnetic activity, leads to strong cloud formation. This eventually limits solar warming of the ocean surface and decreases evaporation with less cloud formation. This entire cycle can be compared to a very effective thermostat, by some aptly termed the water thermostat responsible for keeping global temperatures at a suitable level depending on local conditions