at this moment, it is difficult to answer. CO2 increase may increase food production, but temperature rise may increase or decrease in different areas. O3 rise will decrease food production. But O3 rise is only a rigional problem, not a global problem. also water distribution is another uncertainty. So more work should be done to answer this question.

It WILL not, it IS ALEARDY REDUCING productivity of foodgrain crops. In a 2011 issue of Journal Science, problem of population and food supply, different paers have analysed relationship in food crop production and climate change and found out that both decreasing or rainfall and increasing temperature are contributing to decline in food production worldwide. Disintegration of joint contribution of these these two influences on agriculutre, it has been found out that contribution of temperature rise on declining food production is of several order of that of sporadic precipitation, its deficiency in amount or coverage over space.

Dear Dr Khan,

Thanks for your reply. I agree that productivity of many crops is decreasing worldwide. Technically there should be places where rising temperature should create favourable conditions for these crops. Do you think that farmers of these favourable areas might not have adjusted to expoit the opportunity?

Agriculture and fisheries are highly dependent on specific climate conditions. Trying to understand the overall effect of climate change on our food supply can be difficult. Increases in temperature and carbon dioxide (CO2) can be beneficial for some crops in some places. But to realize these benefits, nutrient levels, soil moisture, water availability, and other conditions must also be met. Changes in the frequency and severity of droughts and floods could pose challenges for farmers and ranchers.

To follow up with Mohammad and Saeed's comments, climate conditions (e.g. temperature, water) may be more favorable in new locations, but there will be some limitations (e.g. predominantly indirect light at high latitudes). Also the historic climate regime may not have produced favorable nutrient conditions for agricultural purposes. Thus artificial inputs (e.g. fertilizer, mechanical preparation) may be necessary to fully utilize the yields lost in other areas around the globe based on changes in climate conditions. Also changes in these ecosystems to agriculture will likely have a negative impact on local flora and fauna, of which many will be already stressed due to the changing climate.

There are (or will be) positive effects in some regions, negative effects in others. To answer the question one has to be aware of the various methods available for the assessment, and the implications of various hypotheses one has to adopt. Not easy to explain in a few words in this blog. Let me give some basic ideas.

Assessment of impact on agriculture is not the same as impact on natural vegetation or other natural processes. For the latter, you assess the POTENTIAL impact "in the absence of any adaptation", then you may introduce some adaptation and evaluate the "residual impact" after the adaptation. Now, agriculture is itself a form of adaptation to the prevailing natural conditions, and therefore the "potential" impact is impossible to define. You have to include at least the spontaneous adaptations of farmers, e.g. changing the date of planting, choosing a different variety of the same crop, choosing another crop, shifting land from crops to livestock grazing, changing cultivation techniques (e.g. some way of retaining more water in the soil, such as planting in contour lines or digging infiltration ditches at a higher altitude in your terrain or microwatershed). For the climate of 2100 to have ANY impact on agriculture, the physiological response of plants to climate is not enough: it is a necessary condition to have farmers that decide to plant a specific crop in that date, based on the economic conditions prevailing in 2100 for that particular crop (price, demand, etc.). This is separate from the question of technological progress (e.g. new varieties appearing from now to 2100): even just sticking to the varieties existing today, you still need to figure out what farmers would do in 2100 if the temperature or rainfall changes in a certain way at one particular location.

For this reason, measuring what will happen to this particular variety of corn if I suddenly grow it under a higher temperature will not give me the answer: farmers in 2100 will not plant that particular variety if it is no longer suitable. These "agronomic model" methods of assessment of climate impact on agriculture are totally inadequate.

There are two main methods in use: Ricardian (econometric) models, and integrated assessment models. The latter are far better. More on this in a subsequent comment.

RICARDIAN MODELS OF CLIMATE IMPACT ON AGRICULTURE. These methods assume that farmers to a certain extent adapt their practices to the prevailing climate and conditions (not a perfect adaptation: just the degree of adaptation observed today). The method is based on a regression analysis of farm returns (or land value), with a sample of farms (or districts) located under different climates. Farm returns are estimated as a function of (a) some climatic variables such as temperature and rainfall along the crop cycle; (b) some technical characteristics of the farm and its farming practices (e.g. presence of irrigation, farm size, mechanization and the like). In general: Y= f(T,R,X) where Y is farm revenue, T is a set of temperature variables (along the year), R is a set of rainfall variables (along the crop cycle or at different seasons) and X is a set of other variables (irrigation, distance to market, general quality of soils, etc.). This is estimated on farms located under different conditions, and the result is an equation giving you the change in revenue for a given change in temperature (or rainfall), controlling for other variables.

This is a static analysis done today. Then you need to estimate the probable growth in agricultural production from now up to, say, 2100, and apply the equation to the production of 2100 expected in the absence of climate change. Remember, besides, that agricultural production techniques are not static: there is a rate of growth in technological possibilities (in the order of 1-2% per year worldwide) plus a rate of possible catch-up progress (especially in developing countries that are not already using the top technology in the world but slowly adopt available improvements). The rate of catch up can also be estimated by observing the difference in the increase of productivity in top-level agricultural sectors (say, the US) and emerging agricultural sectors (say, Brazil). Alternatively, expected agricultural growth in the absence of climate change can be estimated by other means (e.g. by assuming that the rate of growth in agriculture will stand in a certain proportion of growth in total GDP, using then expected GDP as your main projection). FAO, for instance, has an integrated model (excluding climate change) to project agricultural production into the future (now up to 2030 and 2050: references to be given later).

As a result of the Ricardian regression estimate and the projection of agricultural growth in the absence of climate change, you have (a) an expected production in 2100 under no climate change effects, and (b) an expected production under different hypotheses of LOCAL climate change (e.g. under +2°C of LOCAL temperature, and/or 100 mm/year less LOCAL rainfall at the time of planting).

This exercise has been done already. See for instance

Mendelsohn, Robert, 2000. Measuring the effect of climate change on developing-country agriculture. In FAO 2000, Two essays on climate change and agriculture - A developing country perspective. FAO Economic and Social Development Papers No.145. Fao, Rome. http://www.fao.org/docrep/003/x8044e/x8044e00.htm.

The same author and collaborators have prepared a second study (in my view more defective due to small and not representative samples, and lack of worldwide estimates): see:

Mendelsohn, Robert & Ariel Dinar, 2009. Climate change and agriculture: An economic analysis of global impacts, adaptation and distributional effects. Cheltenham (UK): Eduard Elgar.

The general conclusion of Mendelsohn and associates about the worldwide impact may be summarized thus: Not much.

The 2000 study estimates that globally, climate change would INCREASE worldwide agricultural value of production by about 5% (relative to the otherwise expected output of year 2100), with some small decrease in Africa and large increases in temperate and colder regions such as North America, Europe and Northern-Central Asia. The impact of such accumulated 5% difference on the average agricultural rate of growth from now to 2100 would be very small or undetectable. The 2009 study does not provide a worldwide estimate.

All this refers to Ricardian methods (although the 2009 study includes some other approaches). In my view the best approach is not this, but integrated assessment models such as those implemented by FAO and IIASA (International Institute of Advanced Systems Analysis, Laxenburg, Austria), led by Gunther Fischer. On these, a further comment would be needed,

The impact of the economics of food, agriculture and trade are also very important considerations when trying to determine the future of food production. Agriculture does not exist in a vacuum - what investments we make and where, new technologies and how the are distributed and development of new markets at the local, regional and global scales are likely to be more important than climate in the future. Thus I think your question is too narrow - it is very hard to determine how the environment will impact production.

That said, there is a lot of work going on now to better understand how rising temperatures are likely to affect different production systems in today's geo-political and market situation. This work shows, as others have stated, that a changing climate is difficult to adapt to. Many ranchers and farmers are today poorly adapted to climate variability, with low margins and little investment in infrastructure and personnel - thus it becomes even more important to study how markets respond to climate shocks.

The climate has not warmed in the last 15 years. The outlook for this century is global cooling, caused by a secular minimum in the solar activity. The global reduction of temperatures may reduce agricultural yields, due to increased cloud cover and reduced insolation. IPCC has reluctantly recognized this in the draft of their new climate report.

INTEGRATED ASSESSMENT OF IMPACTS OF CLIMATE CHANGE ON AGRICULTURE AND FOOD SECURITY

Integrated assessments use a combination of models: agronomic crop models, agroecological zoning, climate change models downscaled to regions, water availability and withdrawal, economic models (total GDP and agricultural output growth, growth in agricultural trade, changes in relative prices, increasing use of crops for biofuels, etc.), demographic growth models, etc.

Using these models, not only agricultural production is projected, with or without climate change, but also food per capita, and estimates of undernourishment (percentage of people not receiving the minimum amount of food calories).

This approach allows for displacement of agroecological zones, technological progress, changes in the use and management of water, and so on. The number of factors is so huge that normally just a few are considered in each particular report. For this reason one has to read several reports to get the overall picture.

Fischer and collaborators have done two kinds of analysis. First, they have estimated the impact of climate change on RAIN-.FED CEREALS assuming the species and varieties that are sown today, and the lands that are planted today with rain-fed cereals. This is mostly academic, since some land would have to be abandoned and other lands (much more) will be enabled to be grown with rain-fed cereals in high latitudes (US, Canada, Russia, Poland, Kazakhstan and the like); and is also partial because it leaves aside the entire production of rice (which is mostly not rain-fed but irrigated) and other irrigated cereals; it also leaves aside non-cereal crops (which are expected to grow much faster than cereals) and the entire livestock sector. It only serves the purpose of assessing some kind of "potential" effect of climate change, letting farmers only the liberty of choosing the best variety for each expected climate, but barring technological progress. The surprising result is that the potential production of rain-fed cereals in the world will not be negatively affected: in most models the impact is very small, and in most of them the impact is positive (more land in Canada or Russia makes up for less land in, say, the Sahel). This is NOT a prediction of what would happen: just an academic exercise under very unrealistic assumptions.

Other exercises in integrated assessment refer to the entire GDP of agriculture (at constant prices), under various hypotheses regarding demographic growth, economic growth, technological progress, use of first and second generation biofuels, changes in water management, and other factors. The main reports worth reading are as follows:

Fischer G., M.Shah & H. van Velthuizen, 2002a. Climate change and agricultural vulnerability. A special report, prepared by IIASA as a contribution to the World Summit on Sustainable Development, Johannesburg. Laxenburg (Austria): IIASA. http://www.iiasa.ac.at/Admin/PUB/Documents/XO-02-001.pdf.

Fischer, Günther; Harrij van Velthuizen; Mahendra Shah & Freddy O.Nachtergaele, 2002b. Global agro-ecological assessment for agriculture in the 21st century: methodology and results. IIASA RR-02-02. Laxen¬burg, Austria: IIASA. http://www.iiasa.ac.at/Admin/PUB/Documents/RR-02-002.pdf-

Fischer, G., M.Shah, F.N.Tubiello & H.van Velthuizen, 2005. Socio-economic and climate change impacts on agriculture: an integrated assessment, 1990–2080. Philosophical Transactions of the Royal Society, Series B, 360:2067-2083.

Fischer, Günther, Francesco N.Tubiello, Harrij van Velthuizen & David A. Wiberg, 2007. Climate change impacts on irrigation water requirements: effects of mitigation, 1990-2080. Technological Forecasting & Social Change 74:1083-1107. doi: 10.1016/j.techfore.2006.05.021. http://pubs.giss.nasa.gov/abstracts/2007/Fischer_etal.html.

Fischer, Günther; Eva Hizsnyik, Sylvia Prieler, Mahendra Shah and Harrij van Velthuizen, 2009. Bio-fuels and food security. IIASA, Laxenburg (Austria). http://www.iiasa.ac.at/Research/LUC/Homepage-News-Highlights/OFID_IIASAPam_38_bio.pdf.

Fischer, Günther, 2011. World Food and Agriculture to 2030/50: How do climate change and bio¬ener-gy alter the long-term outlook for food, agriculture and resource availability? Included in FAO 2011. Looking ahead in world food and agriculture: Perspectives to 2050. http://www.fao.org/docrep/014/i2280e/i2280e00.htm.

Remember, to finish this review, that food security does not consist in having each country in a situation of self-sufficiency, producing within its borders all the food consumed by its population. On the contrary, all World Food Summits and all scholars in the field insist that food trade is an essential component of food security. This includes both domestic and international food trade. Just as people in one region of a country consume food from another region, and people in towns consume food coming from the countryside, so people in one country may export food to other countries where it is consumed. This has been so for thousands of year. since the invention of agriculture and the division of labour, and is increasingly so in our times of global economic relatedness.

Food security is not defined as national self-sufficiency. It is defined as a situation in which all people at all times have adequate physical and economic ACCESS to food. The first requisite is then that the food is produced; in this regard, what is required is that WORLD production is enough (it is already more than enough for everybody, and will continue to be so in the coming century or more). The problem is not production but access. Physical access everywhere is rather easily enabled by transportation and commerce; the real problem is economic access by individuals and households, which is driven by household income, which in turn depends on economic growth, labour employment, labour productivity and other related variables.

As noted by others, there are many interacting factors, including climate-related impacts on water as well as crops, and interactions between climate and economic factors including world and regional trade in agricultural products. Bioenergy demand and supply and associated regulations are also strongly implicated. Our EU project ERMITAGE http://ermitage.cs.man.ac.uk/ amongst others, is working on modelling some of the less intractable of these interactions.

The impact analyses that I reported earlier were all based on projections of global warming during the 21st century, most of them explicitly using the IPCC scenarios for those projections. This is not equivalent to an unconditional prediction of what will happen: the projections of climate change may be wrong, and in fact the projections are highly uncertain. Thus the logical structure of the food and agricultural impact projections is:

IF (such and such climate changes occur, with such and such regional distribution) THEN (such and such changes in agriculture and food would occur) SUBJECT TO (several other assumptions and hypotheses).

Another aspect I forgot to mention: increased CO2 in the atmosphere has two beneficial effects: it increases photosynthesis, thus increasing yields (especially in C3 crops such as wheat), and reduces water requirements (especially in C4 crops such as maize). Ricardian analyses DO NOT include these effects, which are very important. Integrated assessment models DO include (some estimate of) the effect of increased CO2 on crops.

It is true climate change will increase opportunities in certain areas and will decrease in others as some sub-humid areas are expected to become dry while certain temperate and areas near to equaor are expected to receive more rainfall. But as Hector has mentioned all these are simulations which may are may not happen or may vary over global spaace. Climate change is highly coplex and any projection is tentative. However, we should go with Climate science and should start incremental agricultural planning and adaptation as required by precautionary princile.

So far as impact of atmospheric CO2 on certain crops is concerned, it should be remembered that there is a limit after which stomatal activity of plants gradually dectlines and ceases altogether to take in CO2 to the advantage of the crop and eventually productivity of these crops decline as observed in the countryside of highly polluted areas.

HOW WORLD HUNGER WOULD FARE UNDER CLIMATE CHANGE.

A sample of results by Fischer (2011) cited in a previous comments, about the prevalence of undernourishment in the world (defined as the percentage of people consuming less than the minimum amount of food energy required to stay alive and in good health, the main indicator defined and used by FAO in its yearly reports on The State of Food Insecurity or SOFI).

The prevalence in 2000 was estimated at 13.8%. Predictions for 2050 and 2080.

1. Baseline: FAO projection under no climate change and not considering biofuels. Undernourishment would be 5.8% in 2050 and 1.5% in 2080.

2. Impact of acute climate change under the worst IPCC scenario of explosive demographic growth (A2), not considering biofuels: 5.8% (2050) and 1.9% (2080). Results almost identical under Hadley Centre and CSIRO climate models.

3- Adding the worst scenario for biofuel use of crops. Prevalence would be 6.9% (2050) and 2.1% (2080). Again negligible differrences between Hadley and CSIRO climate models, and also little difference under another biofuel scenario (where prevalences would be 6.2% and 1.9%).

Notice that according to FAO's methodology, undernourishment prevalence below 5% is regarded as non significant due to inherent variability in food needs across individuals due to variability in attained height, household age-sex composition and other factors.

Notice also that all these projections are following a very extreme precautionary principle, assuming the worst on almost everything. Things will not necessarily follow that worst-case path, and in fact they are not following that path already.

Also, note that the precautionary principle is used with a vengeance, because some of the worst-case hypotheses are incompatible with each other, and thus will not occur simultaneously. For instance, if the world increases its GDP to the degree required for projected global warming to occur, it will also decrease its rate of fertility (closely related to per capita GDP) and thus population would not grow so much. Conversely, if population grows explosively, implying that fertility remains very high, that would necessitate less economic growth (otherwise fertility would have fallen) and thus implying less use of energy (which increases with GDP), leading to lower emissions and lower warming. One cannot have it both ways, i.e. one cannot assume high economic growth AND high population growth at the same time.

Unfortunately, current climate change scenarios (up to the latest IPCC report in 2007) do exactly that: they assume a path of economic growth and a path of population growth, independently of each other. So tread carefully.

Fortunately, scenarios to be used in the coming IPCC report due in 2013 just postulate a certain path of emissions, not caring how it is produced, i.e. not assuming anything about population and income.

Visit my Linkedin profile for some of my work on this matter. I am now finishing a new book on the trends and prospects of world food and hunger, not yet available on that site. But keep tuned: I shall post some excerpts or chapters soon.

Dear Saeed,

Probably you are saying that C4 plants like sugarcane and maize will be able to absorb higher carbon dioxide at higher temperature and produce more food.

Dear Anthony,

Thanks for your informative comments. Can you elaborate the effect of indirect light at high latitudes?

Rajesh Rana says: "Dear Saeed,

Probably you are saying that C3 plants like sugarcane and maize will be able to absorb higher carbon dioxide at higher temperature and produce more food."

In fact, the effect of more abundant carbon dioxide in the armosphere will increase yields in C3 plants, but C4 plants like maize will not absorb much more carbon dioxide, not would increase yield by much due to that factor.

What C4 crops would do is require far less water. There are lots of free-air and closed-chamber experiments demonstrating that, with results varying according to method, initial conditions and amount of increase in atmospheric carbon dioxide, with decreases in water requirements ranging from -20% to -60% (in some cases -80%). In existing integrated-assessment projections, such as those by the IIASA team cited before (Fischer et al), a MINIMUM reduction of water requirements is assumed (about -20%), which again shows that those projections are biased towards worst case assumptions in everything, with an extreme observance of the precautionary principle. Things would probably be not uniformly in the worst case for everything: some variables may go according to the worst-case hypotheses, but not necessarily or not likely all of them at the same time. However, such are the principles on which these projections are based, and therefore the projections must be seen as the worst outcome that can be produced, under the really worst hypotheses on a range of possible intervening factors.

The reduction in C4 water requirements would make up for the expected negative impact of increased temperature in most varieties of corn grown in warm regions, even without allowing for change in the variety or cultivar

Of course, one cannot reasonably assume that varieties or cultivars would not change: the varieties and cultivars to be used in 2080 or 2100 would be far different from the ones used today, just as the latter are far different from the ones used in 1910 or 1950; and a large fraction of the improvement in varieties would be specifically selected for the climatic conditions prevailing then, i.e. more temperature and possibly less water, i.e. technological progress would be, to a degree, climate-adaptive, as it has always been.

Dear Mr Rosan,

Will you support or oppose the opinion that wheat production will shift from Australia to Siberia if global warming takes place?

Dear Dr Brown,

Before reading your comments (even before the current one) I used to believe that scientists working in NASA are not permitted to freely interact on a social netwoking site. Anyway, congratulations for your wide perspective on agriculture. Thankfully you talk much beyond aeroponics. However, my perspective is more concentrated on food security issues of India therefore I focus much more on production of food grains.

Dear Dr Khmelinskii,

Yes I have read opinions of some people who believe that Global Warming is more of an activism for exploiting the situation to derive economic benefits.

Dear Dr Maletta,

Thanks for views on Agricultural Philosophy and generous information on models of agriculture.

I didn't know I was talking Agricultural Philosophy: just summarizing empirical research results and conceptual models.

Dear Neil,

I appreciate the sincere efforts of EU to tackle global warming.

Dear Dr Maletta,

Regarding your last comment I think C3 plants like wheat will be benefitted from higher concentration of carbon dioxide to a lower extent and will be damaged by higher temperature to a higher extent. On the other hand C3 plants like paddy will be benefitted.

Dear Dr Maletta,

I really appreciate your comments on the experiments on C3 and C4 plants. It has really added to my knowledge. Regarding my comment on Agricultural Philosophy, I wanted to convey my sense of respect for your views. I have very high respect for Philosophy. If I misrepresented the concept, please excuse me.

Dear Colleagues-

Thank you Dr. Maletta for the concise discourse on C3 and C4 responses to changing temperature and water supply. And thank you Dr. Rana for the thought-provoking question. Certainly the distribution of appropriate and most productive crops will shift as some areas become warmer, or wetter, or drier. However we are also seeing a dramatic increase in weather variability and extreme events. No crop will withstand more hurricanes, tornadoes, droughts, or floods. Because of this increasing instability in weather it seems that the average crop production worldwide would decrease.

Anthony Nguy-Robertson says: "climate conditions (e.g. temperature, water) may be more favorable in new locations, but there will be some limitations (e.g. predominantly indirect light at high latitudes)."

It is true, but of course that means that the crop varieties or cultivars should be chosen accordingly. For example, it would be winter wheat that actually benefits from spending a season under snow while developing a larger radicular tree, before emerging in spring and grow into summer. You would not plant a wheat variety from Sudan under Canada conditions (or the reverse).

Anthony also says that probably the soils would have to be prepared if the soil composition is not good. True again, but not necessarily a difficult obstacle. One does not need to think of planting corn in permafrost or North of the Arctic circle: we are talking about average temperature gradually advancing about 2-4°C over a century. That difference in average temperature usually represents some hundreds of km towards higher latitudes, e.g. moving from Iowa to Minnesota, or from South to North Dakota. If the soils are adequate, you would only need planting in Minnesota the kind of varieties formerly planted in Iowa (of course, there would be progress in varieties along a century: this is just by way of example).

One example that is already observable is the recent expansion of Argentine crops, to the North, West and South of the Humid Pampas plains region surrounding Buenos Aires, due to increased precipitation and slightly increased temperature, i.e. displacement of temperature isolines (to the South) and precipitation isolines (to the North, West and South). The relatively dry Western lands about the middle of the Argentine territory were previously almost useless for crops, and devoted only to very extensive low-productivity cattle grazing. Now they are extensively planted with multi-year grasses (mainly alfalfa), and also rain-fed crops such as soybeans. These leguminous plants deposit nitrogen in the soil. Most of it is done with minimum or zero tillage techniques. Several million hectares of plains were thus incorporated into agriculture, or their productivity vastly enhanced, either for livestock or for crops (or both in rotation). All this process did not involve expansion of irrigation, except a small area covered by complementary/contingent summer irrigation for maize, with large pivots drawing water from rivers or from underground aquifers, in order to water the crop in case of an unexpected dry spell in summer; some richer maize farmers have introduced it (this development of complementary irrigation is not due to increased dryness: in fact the opposite is occurring, but the occasional dry spell occurs).

The Patagonian plateau, on its part, has experienced some increase in temperature but not much increase in rainfall, although precipitation did increase in Western Patagonia, in a multitude of small valleys near the Chilean border; now those valleys (under rain-fed or irrigated conditions) are producing very fine wine grapes, cherries, berries, other fruit, and delicacy vegetables such as endives or echalots, as well as apples, onions, and a lot more (in fact, most of the new areas are tuned to products destined for upper-market consumers and for export, all with high value for volume). Increased summer heliophany (due to high latitude) actually benefits those crops. Wines from Patagonia are all the rage nowadays, but nonexistent 20 years ago.

A map with the change in average precipitation isolines in Argentina (from 1950-69 to 1980-99) can be found in a 2006 UNEP report on climate change and agriculture in Latin America at http://www.crid.or.cr/digitalizacion/pdf/spa/doc16604/doc16604-3a.pdf, page 46-47. Text is in Spanish but the map is clear enough to appreciate the changes even if one does not read Spanish. On average, isolines have been displaced by about 200 km to the West, along a vast territory measuring about 1500-1800 km from North to South (Argentina is nearly as large as India). This trend has continued after 1999, and expansion of crops and crop productivity has also continued to this day (due to climate change and also other factors).

Lynn Carpenter-Boggs says: "However we are also seeing a dramatic increase in weather variability and extreme events. No crop will withstand more hurricanes, tornadoes, droughts, or floods"

Climate projections indeed seem to suggest (but not clearly) an increase in seasonal weather variability along with global warming. But the evidence is thin. It is not very clear or evident, for instance, that extreme events have increased, or variability widened.

For instance, the frequency and amplitude of El Niño events has a multi-decadal cycle of about 30 years. The El Niño events intensified in 1975-1998, after a relatively lull period before that, but up to now the recent period of more intense and frequent El Niños was 1885-1915. There has been a couple of strong El Niño since 1998, but overall the present period does not seem very strong so far. There is no projection of increased intensity of frequency of El Niño in IPCC reports. Recall that El Niño is probably the most important cycle regulating natural variability in world climate.

On their part, studies of trends in the intensity and frequency of hurricanes in the Atlantic, especially those landing on the US territory, measured in terms of normalized damage, show a DECREASING trend along the 20th century (the worst was the hurricane hitting Miami in 1926). Since intensity was not measured before the satellite or aerial surveillance era, intensity of hurricanes is here measured in terms of "normalized damage" (i.e. damage they would have caused with today's population and assets in the areas affected). See on this the studies of Roger Pielke Jr et al:

Pielke, R. A. Jr, C. W. Landsea, M. Mayfield, J. Laver & R.J. Pasch. 2005. Hurricanes and Global Warming, Bulletins of the American Meteorological Society 86(11):1571-1575.

Pielke, R.A. Jr. & R.A.Pielke Sr., 1997. Hurricanes: Their nature and impacts on society. John Wiley & Sons, London.

Pielke, R.A. Jr.; J.Gratz; C.W.Landsea; D.Collins; M.A.Saunders & R.Musulin, 2008. Normalized hurricane damages in the United States, 1900-2005. Natural Hazards Review Vol.9, No.1, pp. 29-42.

Even the drought this year in the US is far from unprecedented: the worst period in recent decades was the 1930s. And besides, attribution of increased variability cannot be based on isolated events, but on increased variance over extended periods. As these things naturally oscillate in 30 year or 60 year cycles or so, being "the worst in 30 years" or even "the worst in 50 years" is of no particular significance, and hardly qualifies as a reason for attributing it to increased variability or to climate change (climate, again, is defined as average conditions over extended periods, so its change is also measured by long-term trends, not by isolated years or over relatively short periods). So again, one has to tread carefully in this matter.

This is an example of the perils of trusting our presumptions, intuitions or impressions about climate trends or about increasing long-term climate variability (which are inevitably based on our own relatively short lifetime experience):

The study by Fischer et al 2002 that I cited in a previous comment retrospectively analyzes the potential production of rain-fed cereals for three 30-year periods along the past century: 1901-30, 1931-60 and 1961-90. They analyzed average yields and intra-period variance of yields. This exercise has only one variable that changes: the climate (crop varieties and agricultural techniques are modelled as constant). The model analyzes hundreds of agroecological zones with land suitable for rain-fed cereals. Their model works year by year, based on historical records of precipitation and temperature at each agro-ecological zone (hundreds of them across the world). Then the mean and variance of potential yields for each period can be computed.

They assumed farmers to take decisions based on the average climate of each zone. But their actual yield would be determined by the actual temperature and precipitation patterns in each particular year. They measured the impact of climate variability on potential yields as the difference between (a) the average of the annual potential yields that would obtain under effective climate conditions in the various years, and (b) the potential yield that would obtain under the average climate conditions for each zone. As expected, climate variability (whatever its intensity) negatively affected yields. Then they looked at the change in potential yields, and the change in the effect of variability on potential yields, from 1901-30 to 1961-90. Such changes would be only due to changes in the prevailing climate (its mean and its variance) from one period to the next. Other variables are held constant.

Well, they found a surprising result. On the one hand, average potential yields increased (by about 8-10%) due to displacement of agroecological zones, higher temperature, etc.

But they also found that the impact of climate variability on potential yields actually DECREASED from 1901-30 to 1961-90. This is the translation into yields of a DECREASING trend in climate variability at the scale of agro-ecological zones where rain-fed cereals are grown.

This refers, of course, to the hypothetical yields that would obtain with the same pool of varieties and the same agricultural techniques along the whole century. This explains why potential yields increased only by 8-10% from 1901-30 to 1961-90. Actual yields along the century increased by much more, several-fold in fact, due to technical progress, but this simulation exercise assumed constant technology and constant quality of seeds. The results are only compatible with decreasing climate variability along the past century, in a vast array of hundreds of agroecological zones across the world, growing about 80 different cereal varieties. Very instructive reading, highly recommended.

REFERENCE

Fischer G., M.Shah & H. van Velthuizen, 2002. Climate change and agricultural vulnerability. A special report, prepared by IIASA as a contribution to the World Summit on Sustainable Development, Johannesburg. Laxenburg (Austria): IIASA. http://www.iiasa.ac.at/Admin/PUB/Documents/XO-02-001.pdf.

In our resent paper "Nielsen at al. 2012. Are responses of herbivores to environmental variability

spatially consistent in alpine ecosystems?", online early in Global change biology, we show that climate change is affecting growth in free ranging sheep in Norwegian mountain areas. However the effect varies not only in strength but also in direction depending on the particluar area, even at relatively short spatial scales within southern Norway. We conclude that climate change will affect meet production but the effect of increassed temperatures will be positive in the north and negative in the south. Altered precipitation patterns will also have contrasting effects, depending on the area under study.

Hi Rajesh

In short, yes climjate change will ikpct heavikly on food production generalkly. There is to be a conference at the University of Nottinhgham in the UK soon to discuss this issue. I suggest you follow the outcome of this confernce closly, and the conculsions they reach. In their flyer they state" The forecasted increasingly variable weather patterns will influence the environment and its ability to support sustainable food production. Major challenges include water scarcity, a decrease availability of key inputs to food production, managing carbon and differing local impacts of climate change. Soil science is at the heart of all these issues". Hope this helps, Kevin

Recently HLPE released a report on Climate Change and Food Security. You may get the answer to certain extent from the report.

Dear Dr/ Mr Tate,

This is true that most of us ignore impact of rising temparature on the availability of fresh water.

Dear Zucong Cai,

Thanks for suggesting the resource. Can you provide some link to the report?

Dear Dr Maletta,

You are a true teacher. I don't undermine your scientific capabilities. But the way you explain things is religious, honest and full of dedication. Thanks you very much for your contributions.

Dear Rajesh Rana,

I just join the group and do not know how to link to the report. I have PDF of the report. I am happy to send you the PDF file if you want.

OK, I find the way to link the report of Food Security and Climate Change. You will find the report in the website:

http://www.fao.org/cfs/cfs-hlpe/report-3-food-security-and-climate-change/en/

at this moment, it is difficult to answer. CO2 increase may increase food production, but temperature rise may increase or decrease in different areas. O3 rise will decrease food production. But O3 rise is only a rigional problem, not a global problem. also water distribution is another uncertainty. So more work should be done to answer this question.

Dear Zucong Cai,

I will be thankful if you send the report on [email protected]

Dear Abdul Jaafar,

Yes prices of food articles may increase tremendously as the world population is continously increasing.

Dear Zucong Cai,

Thanks for the link. Ignore my earlier comment.

Dear Zubin Xie,

I think India and China can share/ collaborate/ contribute a lot towards this issue once the diplomatic priorities of the two nations provide it a higher importance.

I have not yet studied in detail the recent report from the CFS HLPE panel on food security and nutrition, to be found at http://www.fao.org/cfs/cfs-hlpe/report-3-food-security-and-climate-change/en/.

But for the time being I would like to point out just the following:

1. The panel consisted of experts on food security and nutrition, and did not assess the impacts of climate change on agriculture. They relied on outside information in that respect.

2. Section 1.2.4 (Evidence of climate change effects on agricultural production) is not up to standards. It concerns impacts of climate changes already occurred in recent decades, and relies on a single econometric study of current varieties of some crops, grown in current places of cultivation with current agronomic techniques, comparing observed trends in yields with a "counterfactual" (i.e. imaginary) scenario in which the same varieties are grown with the same techniques in the same places but without any trends in climate. This approach is representative of precisely the kind of methodology one should NOT follow in this regard. If the observed trends had not been present, farmers would have behaved otherwise. To use an example I used in a previous comment: if Argentine precipitation isolines had not drifted to the West, but farmers had planted crops in the otherwise semiarid western plains, the yields would have been lower; but in that case nobody would plant such crops in those places, precisely because they were semi arid. You cannot assess impacts on agriculture by assuming that farmers are like robots, mechanically repeating the same actions after decades of climate change. Agriculture is itself a form of adaptation to prevailing climate.

The panel should have done better. FAO has sponsored far superior studies on this matter, using more appropriate methods, especially the integrated assessments conducted by IIASA in close collaboration with FAO. Even the (comparatively inferior) Ricardian models that FAO also sponsored are superior to the naive approach cited by the panel as their only "evidence".

Chapter 2 uses other studies about the future, but most of them are also not satisfactory. Some are definitely substandard; for instance, Cline (2007) uses a model that is not only unable to reproduce the past, but produces NEGATIVE outputs for a lot of countries in the recent past (e.g. Brazil or parts of China appear to have negative agricultural production in the past decades); such models should not be used to predict the future (However, Cline estimates a very small climate change impact on food production: about 2% reduction relative to the much greater per capita production expected in the future).

Other profusely cited models (e.g. Nelson 2010, written by mere coincidence by the team leader of the CFS study) fail to consider the effect of CO2 fertilization and its effect on water requirements. Almost none of the cited studies considers changes in agroecological zones as a result of climate change, or the transformation of livelihoods entailed by expected economic growth (the same economic growth that produces the emissions causing climate change). Most also fail to take into account expected technological change (both technical progress and catch-up increases in the use of existing knowledge): the CFS study prefers to identify current production systems that would be "vulnerable" (if they persist for another century without changes, a very unlikely hypothesis to say the least). Hardly a rigorous way to go.

A further problem is that the presumed difficulties of food PRODUCTION in some areas are equated with problems of food SECURITY in that area. Food security is not about producing your own food, nor is it about national self-sufficiency in food, but about people (i.e. households and individuals of all kinds, urban and rural) having physical and economic ACCESS to food. Physical access to food comes from commerce and transportation. Economic access to food (wherever the food is produced) comes from income, and income comes from education, employment and economic growth. Food availability is not a problem: food is NOT expected to be insufficient under ANY hypothesis, with or without climate change. Food production is already more than sufficient today to feed the world, although access is not universal of course, and according to all projections to the future, even with climate change, biofuels and what not, food will be even more abundant than now, on per capita terms; and this is according to ALL, even the most pessimistic, projections, especially those approaching the problem correctly.

If food security depended on producing your own food, almost none of us intellectuals would be food secure (I, for one, do not produce any food, nor does anybody in my immediate family, but my food security is fine, thank you). Were food security to depend on each country being self sufficient in food, many rich countries that are net food importers would also be seen as mired in food insecurity (from Belgium to Bahrein, from Sweden to Saudi Arabia). The supposed equivalence between local food production and local food security directly contradicts the definition of food security adopted internationally since the 1996 World Food Summit.

My provisional verdict about the report is: probably wanting. Should try harder.

Dear Zucong Cai,

I found the report really worth reading by every contributor on this blog. Thanks for suggesting a valuable resource.

Dear Dr/ Mr Luis,

Thank you very much for your comprehensive coverage on the topic.

Technically, C3 plants (such as cabbage or wheat) which response to CO2 elevation is the increase in photosynthesis, should grow better giving the higher yield. However, C4 plants (e.g. maize) when young, can also utilise "additional" CO2. Moreover, plants need not only CO2, water and light, but also nutrients, hence C/N ratio may be one of the crucial factors of cultivation of a particular species.

Dear Renata,

Thanks for your contribution. Do you think global warming consequent upon enhanced carbon dioxide will help wheat? Please provide your judgment on the heavier aspect between benefit of higher CO2 or damage due to higher temperature in case of wheat only.

Rajesh, at higher latitudes the solar elevation will be lower than that around the equator. While the Arctic and Antarctic circle will experience perpetual daylight, the light will be low on the horizon. This means that there will be less energy (W/m2/year) hitting the surface of the Earth in these locations compared to areas near the equator. Therefore there is less energy to capture and turn into food at higher latitudes. While Hector is correct that we can make improvements to the soil and possibly move crops grown at lower latitudes to higher ones, there will be limits to this movement.

Anthony,

there are limits for everything on this Earth. However, the amount of global warming that is expected according to official projections just means a slight displacement to the North, mostly a few hundred km. This in turn implies not only the annexation of more land to be cropped, but also an increase in the yields of all lands in temperate climes, mostly due to an increase in the length of the growing season, and an expansion of the no-frost period. The balance of all these factors imply (a) an increase in farmland up North (and down South in the Southern Hemisphere), but chiefly (b) an increase in yields and a change in crop mix at all temperate latitudes; in some areas this would imply the possibility of double cropping, as is already happening in several parts (e.g. in Argentina and the US), using short-cycle crops; one of the most common combinations is wheat + soybeans, with zero tillage. This is enabled not only by increased temperatures but by increased precipitation which is expected to prevail in mid and northern latitudes in North America and in Central and Northern Eurasia (as well as in Southern South America except in the Southernmost part of Patagonia, which is however not cultivable at all due to existing dryness).

It is important to recall an often ignored fact: more than 90% of agricultural growth since 1960, and all of it since 1990, is due to increased productivity per hectare, and not to expansion of farm land. World farm land increased very slightly since 1960 to the early 1990s, and is decreasing since 1993; at the same time, agricultural production has tripled since 1960, and its rate of growth has accelerated since the early 1990s (look at the land and production indices statistics at faostat.fao.org). Total farmland is NOT expected to expand by much in the coming decades or during this century, although some expansion of suitable lands will occur at higher latitudes (and also at some higher ALTITUDES) thanks to warming, and some decrease in marginal semiarid tropical areas due to the same cause. (The product of the added lands will be larger than the product reduction in lands no longer suitable, according to estimates).

It is also useful to recall that agricultural employment has grown slowly, is practically not increasing by much right now, and is actually decreasing in most parts of the world (in other parts it is still increasing but very slowly, much slower than total employment). Product per worker has also increased enormously since 1960, and the increase has accelerated since 1990. Thus the prospects for agriculture are not about increasing land or labour, but increasing productivity of land and labour.

Dear Rajesh, I am not sure whether elevated CO2 can positively affect wheat, as it inhibits nitrate assimilation (Bloom et al., 2010, Carbon Dioxide Enrichment Inhibits Nitrate Assimilation in Wheat and Arabidopsis. Science 328, 5980: 899-903.). The matter is complicated and complex in every aspect, so there are no clear answers :(.

The idea of 'shifting production centers' is easier said than done. Just think of the massive infrastructure changes, social structure upheavals, and new knowledge needs that will accompany such a shift. And then add to that the idea that there is no 'new and stable normal', if climate change happens rapidly. That means this shifting may continue to be necessary forever. This is not an easy future to contemplate.

Hector, I agree that climate change will be a displacement of a few hundred km. Double cropping does have the potential to help make up the loss in yields in other parts of the world. However, one thing increasing temperature does is trap more moisture in the atmosphere. This means longer periods of dry weather with more intense rain events. These farms may not receive rain at appropriate times for maximal yield and excessive rains may cause flooding, reducing yield. Thus in addition to preparing lands for different crops, farmers/policy makers will also need to discuss water storage options to minimize the effects of drought and flooding that is likely to increase with climate warming.

Renata Baczek-Kwinta and Molly Brown: I am being notified by ResearchGate of your request for a publication of mine. Please contact me at my address (hmaletta at gmail.com).

Dear Renata,

Thanks for suggesting an important resource and clearing one of my doubts.

Adam, just see what has happened in Brazil and Argentina along the most recent two decades. Brazil has added about 20 million hectares in the 'Cerrado' region (a long sabana and bush area between the Eastern coastal plains and the Amazonian forest); Argentina has added several million Ha of cultivation to the West and North. Total grain production has tripled in Argentina, and a similar increase (proportionally not so large) in Brazil. Of course, transportation infrastructure is a key accompanying factor, and suitable investments have been made, especially in Brazil where it was most lacking; Brazil has opened lots of roads and also waterways for transportation of grains from the Cerrado towards the Atlantic coast. Argentina did not need to do likewise to the same extent, because most of the roads and railroads where already there (although more should have been done if only governments had acted more efficiently and with more foresight in this regard).

Regarding storage, a revolution is occurring with the use of comparatively cheap giant plastic 'sacks' (50-100 m long, 3-5 m in diameter), that commercial farms use to store the grain in the field, from harvest to sale, making old metallic silos mostly obsolete and greatly curtailing the cost. It has also made much middlemen storage redundant, and has allowed farmers to avoid selling all the product right after the harvest for lack of storage capacity).

Just the added taxes coming from the increased production and revenue pay for all the infrastructure required. And the required investment can be spread over many years in the case of climate change, since it is veeeeery gradual.

Another example of expanded farmland, not due to latitude but altitude, is to be found in the High Plateaux around Lake Titicaca in Western Bolivia, and to a lesser extent in Southern Peru, a Highlands area at great altitude (3700-4000 metres above sea level) once affected by frequent frost even in summer that killed crops at flowering or grain filling stages, and where only a limited amount of low-yield potatoes or barley was grown. Large areas of that region, where temperatures and precipitation have increased, are now covered with cultivated pastures (such as alfalfa) and other crops like barley and quinoa that have greatly expanded their coverage. Quinoa sells extremely well in world markets, it grows mostly at specific microclimates at high altitude, and its production has greatly increased due to this warming of the High Plateaux and the resulting decrease in unseasonable frost.. Precipitation has also increased, further facilitating the process.

Dear Anthony,

Thanks for your clarification. Dr Maletta's opinion explains the practical scenario that we may have to face in near future.

Anthony Nguy-Robertson says: " one thing increasing temperature does is trap more moisture in the atmosphere. This means longer periods of dry weather with more intense rain events."

Right, it can happen. Do you know of any example in which this caused a reduction of yields? I have not found any. The examples I know (in Northern and Southern America) do not show any significant case of that kind. The new lands that are enabled for cultivation (e.g. in Argentina) were previously too dry, and now receive some more precipitation, and as a result the soils can be cultivated (even accounting for any increase in atmospheric humidity). In other places, that were already cultivated but now receive more rainfall, the net effect is the same: more yield.

The resulting yield is probably not "maximal" compared with growing the crop at the "optimal" location, but that is idle dreaming: you grow crops where you can, and the "optimal" yield is the one you can reasonably obtain, ON AVERAGE, given the climatic and technological conditions. At any rate, obtaining any yield where none existed before (and this without any enabling subsidies from the government, as is actually the case) is always a gain.

By the way, during the recent 10 years the Argentine government has heavily taxed farm exports (thus also depressing domestic prices), while not subsidizing agricultural inputs. The implied subsidy is actually negative.

Anthony also said: "These farms may not receive rain at appropriate times for maximal yield and excessive rains may cause flooding, reducing yield. Thus in addition to preparing lands for different crops, farmers/policy makers will also need to discuss water storage options to minimize the effects of drought and flooding that is likely to increase with climate warming."

In fact, one thing of which I do have some evidence is unexpected flooding in some formerly dryer regions. Not a big deal but worth considering. In the western plains of Argentina, some 400-500 km west of Buenos Aires City, some investment had to be done in the 1990s to facilitate drainage, which had not been foreseen when roads and railroads were built. This involved widening of culverts, digging some canals, and designating some lowlands as floodplains. Also in Oruro (Bolivia, right South on Lake Titicaca) some flooding has occurred in 2004-05 and other years, where few occurred before.

As these are all plains with little slope, drainage is not easy, and there waterlogging may last for months; but drainage can be facilitated by wider culverts along roads, designation of local flooding areas, and other similar works. The cost of this kind of work is relevant, but is not very high. There have been no floods in the relevant area of Argentina during the last 10-15 years, to my knowledge, due to improved drainage. In other areas, where rainfall was already high to begin with, the increased precipitation has not caused much trouble, because the drainage infrastructure was already in place. Some similar works have been undertaken in the relevant area of Bolivia, but I do not have an updated picture on that, and the flooding episodes of that kind remain rare there, because overall the area is still pretty dry.

Seasonal flooding, on the other hand, is frequent in the Andes, because rainfall is concentrated from November to March, which is the Southern Hemisphere summer, when little water becomes frozen as ice, and there is a dry season from April to October (in winter) during which crops are not normally grown (even in irrigated areas) because temperatures are too low and rainfall almost non existent. Notice the difference of this pattern with Alpine locations in the Northern Hemisphere, where rainfall and snowfall occurs mostly during the winter, most of it becoming ice, which is in due course melted in the spring when it runs downhill to water growing crops; nothing of the sort happens in the Southern Hemisphere tropical and subtropical Andes, which have a rainy summer and a dry winter. .

"Right, it can happen. Do you know of any example in which this caused a reduction of yields? " I do not have examples where 'climate change' has cause a loss in yield due to inadequate rain (no one will point to one event and say that was caused by climate change); however, there are plenty of papers discussing how to maximize yield through optimizing irrigation (e.g. [http://www.sciencedirect.com/science/article/pii/S0378377498000699], [http://colleges.ksu.edu.sa/Papers/Papers/IRWATERALLO.pdf]). This is the same concept with 'poorly timed' rain. If the falls outside of the growing season, or outside of critical stages for growth and yield, then it is 'poorly timed' and thus wasted water unless you can store it for later use.

Here in Midwest United States (Indiana, Illinois, Iowa, Minnesota, Nebraska, South Dakota) we are currently experiencing a major drought (worst since the 1950's). Fortunately for Nebraska we have irrigation (from one of the largest aquifers in the world) which has help salvage some of our yield (although the excessive heat has reduced the yield quite a bit). This is following major floods from last year, in which many farmers lost their farmland near major water ways (e.g. large inputs of sand, high water through the growing season, etc.).

This is why I stress there is a need for water management in order to balance these two extremes. Allowing some areas to be flooded periodically as a storage buffer, or by reintroducing wetlands into the water systems, will provide longer storage times, especially in areas of higher rainfall. Growing up in Indiana (it is wetter in Indiana than in Nebraska), we have major drainage systems to remove water from our farmlands and directly into waterways/streams/rivers, whereas in Nebraska there is little to no waterways/drainage in the fields. Putting in wetlands will increase water storage capacity and reduce flash flooding caused by drainage systems on farms. Farmers generally do not include these buffers due the loss of yield from no crops being planted in that area; however, there are long-term benefits to this strategy (e.g. [http://www.iowadnr.gov/portals/idnr/uploads/Wildlife%20Stewardship/cp27_28.pdf], [http://environmental.science.dal.ca/Files/ENVS_Thesis_Projects/2011/SimonGreenland-Smith.pdf]) and many local/state governments in the USA are implementing programs to encourage farmers to do this.

Similar strategy to this described by Anthony is promoted in European countries. Till 1980's, the governments of the Central European countries used to put the emphasis on land drainage in order to obtain more farmlands. Nowadays it has turned into more sustainable water management. The farmers who possess the wetlands use the biomass instead of crops, and in some endangered regions they are given financial amendment in the case of flood. As we have had two big floods in last 20 years, some of thePolish farmers clearly understand the need for keeping such a buffer.

"Climate Prediction and Agriculture: Advances and Challenges" Springer Verlag Berlin Heidelberg 2007 Eds. Mannava, V.K. Sivakumar, James Hansen

Hansen has been at this sort of things for years. -- even tried to convince the Bush and Obama bomber team that climate changes will effect agriculture. One little note from my studies C3 crops will do well or not well while C4 crops will do well or not well under different and changing conditions. The social factors are greater then the so called advances by techno fixers, in that the techno fixers will help agribusiness but not most of the farmers where techno fixes either cost more or are not likely to get to them, since the agribusiness -- sorry for this -- let's realize there are profits to be made in crisis, worst scenarios, droughts and floods. Sooooo the smaller less capable of adapting farmers will take to walking to another country.

rgd

phd

Although this paper is more focused on soil pollution and the influence of some changes on climate, this could be of interest for some of you.

http://dx.doi.org/10.1016/j.envpol.2011.03.029

Dear all,

So far we shared opinions on possible impact of global warming on agricultural production. I thank all contributors for their valuable input. I think the discussion needs to be extended to cover potential measures for mitigating the impact of global warming on agricultural output. Please provide opinion on HEAT AND DROUGHT TOLERANT CROP VARIETIES, CARBON SEQUESTRATION MEASURES and other required technological initiatives to tackle this problem.

Please pay attention to changed question.

Regards.

Rajesh K Rana

Dear Rajesh, One of the challenging aspects of climate change is that the scale at which it is felt is very broad, and the impacts felt at any one location can be extremely varied. Heat and drought tolerant crop varieties are being worked on, but their distribution and impact will likely be very limited due to the necessity of industrialized systems where farmers pay for seeds. Today 85% of all food is grown and consumed locally, and although international trade in commodities is expanding, it still only serves the well-off urban populations. Most food is based on inexpensive grains grown locally using broad phenotypes and diverse crops in subsistence systems, thus the high-tech 'improved crop varieties' you speak of are quite irrelevant.

In the broader food system, climate change is likely to result in much more extreme weather which will impact food security at multiple levels (urban, rural, rich and poor) and severely challenge our ability to further develop agricultural systems. Thus I wholeheartedly agree with the comment by Nguy-Robertson - water management is absolutely required and is necessary across all agricultural systems, not just those in the developing world. We need to produce more in years with good weather so that we can maintain adequate consumption for the poorest populations in years with droughts and floods.

Dear Molly,

Thanks for your valuable comments. If I say that no nation in the world would be in the business of exporting food grains and whatsoever stuff will be sold in the international markets will essentially be surplus production above food security requirement of the developed nations, or economically imrportant exports from underdeveloped/ developing nations to meet foreign exchange compulsions; then would you call me wrong or right?

The idea that "the nation" would export only what is a surplus over the nation's food needs is, in my opinion, a bit simplistic. Nations do not produce or export: it is farmers (and traders) who do. And the product is not an undifferentiated stuff that can be put to this or another use: it is composed of hundreds of specific agricultural products, of animal or vegetal nature, that farmers choose to grow because there is a market for it (no matter whether the end market is local or global). The decision of farmers is taken on the basis of convenience (broadly defined): costs, prices, suitability, accessibility of markets, and so on. "Nations" (i.e. governments to be more precise) may intervene in these affairs, e.g. setting taxes on imports or exports, or subsidizing this or that, but the base process is at the level of economic agents such as farmers, consumers, traders and so on, at home and abroad.

The "food security requirements" of "nations" do not consist in producing all the food their citizenry needs, but on securing sufficient economic activity and resulting income, for the people to be able to access food. And in most developed countries, securing food is not the greatest consideration: it would be accessible in any case; most pressing concerns are, for instance, securing energy, or making the economy at large more competitive, or attracting capital to their shores, or protecting the worth of their currency. Access to food is a consequence. And it is not equivalent to producing enough food: the US is a large food producer and exporter as a country, but supports millions of people with food stamps, to make them able to access food, and the USDA survey detects millions that feel they are food insecure (not having enough access to food, or fearing they would not in the near future).

On the other hand, of all the increase in agricultural production in the latest half century (since 1961) more than 90% comes from increased production per hectare, and only a minor fraction from additional land. And the increase in land occurred almost entirely before 1990: agricultural land has been stagnant and slightly decreasing in the latest two decades. Since production growth accelerated lately, productivity growth accelerated even faster due to stagnant use of land. That includes the entire world, with little variation, from India to the US, from Europe to Africa. Productivity has been growing in all countries, but especially in developing ones, with the important news that it is also accelerating and growing rapidly in Africa, which lags the rest of developing countries by about two decades.

This increased output per hectare (valued at constant prices) comes from increased yields in every crop, but also from changes in the crop mix (generally away from cereals, which grow the least because their demand is not quite elastic), changes in varieties and cultivars taking advantage of new seeds, changes in water management and cultivation techniques, and changes in composition of production between crops and livestock.

Technical note: the concept of production used here is: value of net agricultural production ("net" because production used as seed and fodder within the same agricultural sector is excluded to avoid double counting) valued at world-average constant prices, where the world average is based on domestic producer prices converted into a common currency by purchasing-power-parity equivalences, as given in FAOSTAT's section on production indices. This specification ensures that measurement of changes over time, and aggregation across countries, are not affected by changes in absolute or relative prices, or by changing degrees of misalignment in exchange rates,

We are evaluating variability of climatic parameters in our condition , it is observed after very long time( 50 years) little change in temp. is observed , so nothing worry about it, because every new generation will have habit of bearing slight ... negligible temperature,

How ever green house technology already proven one for any level of controlled temperature cultivation.

Carbon sequencing is good, but very long process to cool down earth.

Dear Dr Maletta,

You have rightly said that the nations that don’t follow area planning (states issue permits/ quota of area under different crops) try to regulate area under various crops through policy initiatives in the long run. I personally feel that long term export policy of any nation will influence area under crops in such a way that more and more export of high value and high margin crops/ commodities is possible.

Dear Vekariya ji,

Can you elaborate what experiments on climate chang are taken up at JAU?

Rajesh, your ideas about area planning or government regulation of areas under various crops or long term export policies may be right, but I have not said such things. In fact I am rather sceptical about the capabilities of governments (especially those of developing nations) to impose such kind of planning decisions on the complex and interdependent national economies of today. Such policies have the nasty habit of backfiring, or creating new problems, or going nowhere.

What I did say or imply is that the government of a country, if it understands how the world works nowadays, would try to defend the worth of its currency, establish sound economic institutions and clear rules of the game (coherent with the world economy) allowing economic agents (domestic or foreign) to operate on a reliable economic environment, and to get capitals (domestic and foreign) interested in investing in that country rather than elsewhere.

Dr Maletta thanks for your clarification.

Dear Rajesh, one aspect to this debate concerns the relative performance of different crops and knowing how best to manage a basket of agricultural crops in the most efficient way to meet food, feed and industrial needs. A sister institute to our own - CIAT (I work at IITA) - has done a lot of research on this aspect. One of the most dramatic findings of this climate modelling work was that cassava looks set to do significantly better that currently under future climate changed scenarios. This probably effect appears to be so strong that CIAT are referring to cassava as the 'Rambo Root'. To have a look at this story and the kinds of climate change research they are doing, please do check out their website.

http://www.ciatnews.cgiar.org/en/tag/rambo-root/

i concur with J.Legg's comment. Cassava is in fact one very important staple crop in tropical areas which would not suffer (on the contrary, it may benefit) from a rise in mean temperature.

In other areas of the world, e.g. at mid latitudes, the effect of a rise in mean temperature could be rather easily countered by adopting varieties that are currently grown at somewhat lower latitudes (e.g. growing in the Northern US the varieties of corn now grown in Southern US), even without any further progress in seed selection and adaptation,. But in the hottest parts of the world there is no hotter parts to delve in for adapted crops.

On the other hand, always remember that the output that would be affected by climate change is not the output of today, but the output of tomorrow (especially in the second part of the 21st century). In the meantime, technical progress (even at a decreasing rate of progress) would increase land productivity, and the structure of supply and demand would also shift towards higher-value crops due to increasing levels of income (the increasing levels of income are a necessary implication, since the climate would change due to increased CO2 emissions, which would increase due to increasing GDP, total and per capita). According to existing estimates, world food production (valued at constant prices) by 2080-2100 would be about 4-5 times the level of today (with a populatipon barely 25% higher); the effect of climate change would be in the order of 5% (plus or minus depending on the models used) relative to that future output. So without climate change, a current food supply of 100 would turn into 400 or 500; with a negative impact of climate change (-5%), future food output would be 380-475, still four or five times the level of today. Even if the impact is not only negative but twice the estimated amount, i.e. -10%, this projection stands.

So the problem is not "to maintain agricultural production" (as it was expressed in the original question): it would grow anyway. In fact, it is expected to be high enough to eliminate undernourishment by 2050 or shortly thereafter, according to FAO and IIASA (very conservative) projections, even after accounting for the worst scenarios of climate change and a large increase in the use of food crops for biofuels. I can provide references on request.

Get used to the reality - Anthropogenic Global Warming as peddled by IPCC is a hoax.

We do not have a climate problem, because the IPCC models are wrong, which had been amply demonstrated by Lindzen and Choi in 2009. See the details here: http://clima-virtual-vs-real.blogspot.pt/2012/06/scientific-method-against-anthropogenic.html

Therefore, this entire discussion is pointless - we are entering the new Little Ice Age, which will happen regardless carbon sequestration and the rest of the useless stuff we may be doing, unless someone knows how to make the Sun shine brighter during the next 80 years.

We should be solving exactly the opposite problem - how to avoid mass hunger when the temperatures and the agricultural yields plunge down in the following decades.

Global warming is clearly something that inspires strong opinions. I have to admit that I am not close enough to the research to make a specific comment on its legitimacy. However, this is one of those issues like evolution, where factors other than science influence peoples views. In such cases, and where they have been subject to extensive study from all angles, it's almost always best to respect the consensus viewpoint. Obviously the earth goes through long-term climatic changes, and this applies just as much as it did in the past. The scary thing, however, is the temperatures are rising at an alarming rate, quite unlike the pattern that occurs during the usual geological-scale climate cycles. What is sad is that we continue to destroy our planet, in so very many ways, and yet look for excuses to explain away the destruction. On the current track, it's certain to be a calamitous future. OK for us, maybe to continue on our destructive path, but so so sad for those that will come after us.

James,

you say that "The scary thing, however, is the temperatures are rising at an alarming rate."

Well, in fact, global temperatures increased from about 1970 to the late 1990s, but since the mid or late 1990s to the present, the global temperature trend has been flat. Statistically equivalent to zero, according to the global mean temperature dataset compiled by the University of East Anglia (Climate Research Unit). Look at the graph here (Jan 1997-Aug 2012):

http://i.dailymail.co.uk/i/pix/2012/10/14/article-2217286-157E3ADF000005DC-561_644x358.jpg.. A longer graph (since 1850) is here: http://postimage.org/image/o1zqniq21/full (better appreciated by looking at the lower graph with the running annual mean). The dataset itself is at http://www.metoffice.gov.uk/hadobs/hadcrut4/ . Note that the graphs reflect "anomalies" i.e. deviations from the mean. These data are from meteorological stations around the world, but they also coincide with satellite measurements available since 1978.

The assessment of a currently flat trend is equally valid (with minor differences) whether you start in 1995, 1996, 1997, or 1998, i.e. for the latest 17, 16, 15 or 14 years. Note that this nearly-flat trend is not without annual variability: in 1998 there was an unusually high temperature season due to El Niño, followed by an unusually cooler one in 1999 for the opposite phase of that cycle (La Niña). Similar ups and downs happened also in 2006-07 and 2009-10, yet the overall trend is flat.

This recent flatness does not mean that "global warming has ended": the overall trend since 1850 is indeed upwards, although the trend is somewhat masked by several 60-year cycles composed of alternating 30-years periods of warming and 30-year periods of flat or decreasing temperatures. The latest warming period was about 1970-1998, following a stable or slightly cooling period in 1940-70, which followed a period of warming in 1910-40 after a slightly cooling period in 1880-1910, and warming in about 1850-1880. These ~60-year oscillations around the long-term trend are probably natural. The current flat period (about 15 years long, depending on the cutoff point) might or might not be the first part of another 30-year flat or slightly cooling period.

Once these multi-decadal cycles are removed, the remaining overall trend in 1850-2012 is slightly upwards. Global temperature has increased by about 0.8°C between 1850 and 2012 (a period of 162 years) equivalent to about 0.5°C per century, or 0.05°C per decade, which rises to about 0.08°C per decade if one counts from around 1900. (Notice that comparisons are more reliable if comparing the mean of two periods of several years each, rather than individual years, and should start and finish at periods covering a similar phase of the 30-year cycles, e.g. low-to-low or high-to-high).

This long-term warming tendency is commonly regarded as the probable effect of two main factors: (a) a secular warming recovery after the so-called "Little Ice Age" that lasted from about 1450 to a low point reached about 1820-50; and (b) an added warming contributed by greenhouse gases emissions, especially in the 20th Century,. The relative shares of these two warming factors are quite uncertain.

Very nice answer, Hector. It's never very helpful to use such strong and unscientific terms as 'alarming' in the context of a discussion of science, so I stand corrected. However, the likelihood of added warming attributable to greenhouse gases should be enough in itself for us to strengthen efforts to reduce greenhouse gas emissions. Probably more important than global warming, arguably, is the environmental destruction associated with greenhouse gas production, such as cutting down of large areas of forested land, in order to open it up for development and agriculture. In Tanzania, where I live, this is happening before our eyes. With the lack of collective will to stop this destruction, it's hard to see a promising future for the planet. But then, since we won't be here, maybe it doesn't matter?!

James,

besides the strong ideological claims on both sides (from allegations that greenhouse gases (GHG) do not warm the atmosphere, to allegations that it would cause a catastrophic warming in a matter of a few decades), the more scientific debate is over much narrower questions. The main one is precisely about the size of the greenhouse effect, the so-called climate sensitivity of GHG, especially those GHG emitted by humans, i.e. CO2, methane and a few others, which are usually expressed in CO2-equivalent terms. Climate sensitivity = increase in mean global surface temperature per doubling of CO2 concentration in the atmosphere. The DIRECT effect of CO2 is about 1.1° per doubling; then there are feedbacks, positive and negative. A positive (reinforcing) feedback is for instance that the direct warming effect causes an increase in water vapour in the atmosphere, and this water vapour is a greenhouse gas that further increases surface temperature. A negative (attenuating) feedback is for instance cloudiness: if the increased evaporation and water vapour causes an increase in clouds, this tends to block sunlight and thus cool surface temperature (clouds are water in LIQUID state, i.e. droplets, and only part of the increased evaporation goes to clouds). The net effect is very uncertain (estimates of total sensitivity vary by a factor of 3-4, from about 1° to about 4° per doubling). So far we have had an increase in CO2 of about 50% since preindustrial times (current 400, preindustrial 270), and TOTAL temp increase has been about 0.8°C, part of which is natural. The part due to GHG is surely less than 0.8°C, possibly about 0.5° since it is piggybacking on the ongoing recovery from the Little Ice Age. Thus 0.5°C for an increase of 50% in CO2 concentration. This would imply an actual sensitivity of about 1°C per doubling, corresponding to a net feedback of 0%, i.e. positive and negative feedbacks offseting each other. If by a stretch of imagination we were to suppose that ALL the increase in temp since preindustrial times is due to GHG (as if the natural Little Ice Age had not ended), it would mean a sensitivity of 1.6°, but this is surely an overstatement. Some estimates of sensitivity go much higher, of course, but the historical experience so far does not seem to validate them.

However, no scientist would PREDICT the future climate. All they could decently do is ASSUME a value for sensitivity (and other parameters), ASSUME a scenario (trajectory) of emissions along the 21st century, and as a consequence PROJECT what would be the increase in global temperature. With a convenient choice of reasonable values for the parameters you can get no warming, little warming or more warming. And most models (especially those assuming high sensitivity) still mostly ignore the effect of clouds, because the effect of CO2 on cloudiness is (to put it mildly) not well understood so far.

The solution may not be drought tolerant plants, but providing more water through

use of irrigation. We may also need to use green houses, and concentrate the CO2 in these Green Houses to promote plant growth. The alternative is to stop using

carbon as an energy source, and begin using more renewable energy sources.

Both are important, Michael. But new irrigation systems are often costlier than just using a more suitable variety as the climate goes a-changing.

to Hector:

You have forgot the important one: we are in for a Little Ice Age, despite what IPCC may or may not predict. It is happening as we speak.

Note that IPCC reports are pseudoscience, in that they never tried to question the AGW hypothesis in the first place. The IPCC climate models are wrong, as Lindzen and Chou demonstrated (see the references in our paper). Therefore, IPCC climate predictions are sheer nonsense, apart from being simply wrong -- the temperatures are not increasing for the past 15 years, whereas they predicted (and still predict) a monotonous growth. Wake up.

Article Climate Change Policies for the XXIst Century: Mechanisms, P...

Igor, you may be right, but my position is not as radical. The present thread is not about the quality of IPCC climate projections, but about what to expect as IMPACTS on human affairs, for instance in agricultural production (my own theme) or other subjects (e.g. sea level rise). Current understanding after the 2010 IAC evaluation of IPCC procedures is that the report of IPCC Working Group II about impacts and adaptation is appallingly poor, even compared with the report from Working Group I on the scientific basis which may have problems of its own (such as understating uncertainty). As I am not a physicist or climatologist, I cannot seriously say much about coupled atmosphere-ocean models and all that, though I've read a lot on those subjects: I prefer to concentrate on the issue of impacts, especially those impacts I am more prepared to discuss.

My own recent book and articles on the matter (see refs and links in my Linkedin profile) take climate projections as a given, although disputing some lateral issues such as population and income projections, and concentrate on how to define, measure and project impacts on food and agriculture. In this particular matter, and in spite of some ill-informed reports using flawed methodologies, the general conclusion so far is that the impact would be very limited (slightly positive or slighthly negative depending on the study), and that impact would act on a level of food production that (by 2050 or 2100) would be much larger than now in total or per capita terms. Even FAO, which usually tries to call attention to negative trends regarding food security, projects the world situation progressing to a non significant level of food insecurity (undernourishment) by 2050;; even in the projection for the worst region (Sub-Saharan Africa) the level in 2050 would be only barely significant and would become non significant shortly thereafter, all this using extremely conservative or pessimistic hypothesis about progress in agricultural technology, climate change, and future use of food crops as fuelcrops.

Of course, this can be altered in case the climate cools down or fails to warm: vast land areas in temperate zones (Canada, Russia, Northern Europe or Argentina, to name a few) would not enjoy the expected improvement in yields, expansion in cultivable land area and lengthening of the no-frost period that would result from increased temperatures, and this effect would probably outweigh the lack of deterioration in some tropical or Equatorial areas that are expected to worsen their agricultural potential. However, even in that case the effect would also be relatively small, especially because population growth is already rapidly slowing down and population is expected to stabilize later in the century.