The empirical evidence is easy. It's the scientific proof that has error bars.

The world climate has been stable for a long time, and it is changing rapidly now.

https://en.wikipedia.org/wiki/Temperature_record_of_the_past_1000_years

Presence of atmospheric pollutants and changes in solar irradiance have the most significant influence on global climates. Changing the albedo could have an effect, but it proves to be fairly small globally. Releases of anthrogenic sources of heat is completely inconsequential. Changes in land use affects evaporation, creating heat islands in cities, but these don't make a significant difference overall.

https://climate.nasa.gov/causes/

https://www.epa.gov/heat-islands

https://www.universetoday.com/39937/albedo-effect/

https://scied.ucar.edu/planetary-energy-balance-temperature-calculate

https://en.wikipedia.org/wiki/Primary_energy

CO2 concentrations are connected tightly to all previous climatic events, but there is insufficient data to determine cause and effect.

https://www.johnenglander.net/chart-of-420000-year-history-temperature-co2-sea-level/

I think it is safe to say that in the geologically recent past, we have no example of CO2 levels at the current concentration. The last time these levels were reached, the oceans up to 20m higher than they are today, because of a loss of glacial ice mass.

Article Relationship between sea level and climate forcing by CO2 on...

Sea levels have been fairly steady for the last 5000 years - rising an average of about half a millimeter per year over that time. They have been effectively flat for the last 2000 years.

https://www.iceagenow.info/whats-new-sea-levels-rising-10000-years/

In the last 100 years, sea levels have been rising more rapidly.

https://en.wikipedia.org/wiki/Sea_level

Rise is currently about 3.5 mm/yr. Something has changed the 2000 year 'flat line' to the current 'rapid rise' - comparable to the rate the climate was changing at the end of the last ice age. When we look at all the possible causes, only GHGs have the potential of producing the observed effect. And CO2 is the most significant GHG above the clouds (eg, above the principle emitters of longwave radiation).

In the very recent past (the last few hundred years), we have seen a change in the amount of individual pollutant emissions that would individually be expected to raise or lower the net energy flux. The two pollutants that are currently contributing the most to forcing is CO2 and Methane - both of which are being shifted out of their pre-historic balance by human activity.

http://www.global-greenhouse-warming.com/radiative-forcing.html

https://en.wikipedia.org/wiki/Greenhouse_gas

That's the empirical evidence. It's easy.

Douglas Nuttall Thank you for this substantive and honest response. There are a nonetheless a couple of counterpoints i would like to make. You agree that “CO2 concentrations are connected tightly to all previous climatic events, but there is insufficient data to determine cause and effect”. We also now that CO2 sometimes follows and sometimes leads warming on the paleoclimate scale, so even mere correlation is not consistently there. The strategy for showing that CO2 causes Global Warming appears to follow an argument by elimination of other causes, based on estimates of other influences based on theoretical climatic models. At the core of this stratgy is the belief that CO2 is a heat trapping greenhouse gas, but this is only part of the truth.

CO2 is not only a heat-trapping gas in the troposphere but becomes a cooling agent in the Stratosphere due to longer intermolecular path. “CO2 is the primary radiative cooling agent and fundamentally affects the energy balance and temperature of this high-altitude atmospheric layer.” (https://www.nature.com/articles/ngeo1626) Currently there is a “global increase in COx (CO2 and CO, combined) concentrations of 23.5±6.3 ppm per decade at an altitude of 101 km, about 10 ppm per decade faster than predicted by an upper atmospheric model.” This suggests that a substantial portion of CO2 migrates to altitudes where, according to Emmert (2012), “thermal energy is transferred via collisions from other atmospheric constituents to CO2, which then emits the energy as heat that escapes to outer space.” https://phys.org/news/2012-11-atmospheric-co2-space-junk.html We thus know that Earth’s atmosphere is actually leaking more heat into space due to increased CO2, not gaining it. This does not of itself entail that the lower troposphere is not warming, but the upper atmospheric cooling must affect the lower troposphere via convection so the two effects to some degree counter one another. We just dont know what is the net effect of CO2, as it could plausibly be negative as it evidenctly causes the Entire atmosphere to lose more heat into space, that is, it is technically know to cause net atmospheric Cooling.

Considering how divisive, aggressive and dangerous the debate about global warming has become it is crucial to either acknowledge what we dont know, that there is a huge uncertainty, or find better quality, more direct evidence of the alleged warming effect being driven by CO2.

I am not sure that the data as presented doesn't support the hypothesis. If CO2 is good at absorbing long wave radiation, then it is also good at emitting it. The upper atmosphere cooling makes as much sense as the lower atmosphere heating due to GHGs. Your statement of 'We thus know..." misinterprets reality - we know that it can emit the same amount of heat as it is gaining, but at a lower temperature. But there isn't more energy to emit.

The issue isn't really about understanding precisely what is the cause, the mechanism, and effect. An empirical relationship doesn't care about the mechanics - it worries about outcome alone. There is a tremendously strong empirical relationship within the last 400000 years between climate change, ocean levels, and CO2 concentrations. The underlying cause of just about all of our existential issues is that humanity is not currently acting in a way that will allow long-term survival of our existing population, so our existing population has a moral obligation to itself to attempt to limit the magnitude of the catastrophe(s) of our own making.

If humanity has exacerbated any of the natural cycles (and it appears to have, based on timing and CO2 concentrations), then you and I (and 7 billions of our friends) share in the moral responsibility of addressing the upcoming crisis.

If you choose to accept your share of the moral responsibility by encouraging and enabling the ecological migrants - say those living within 10m vertically of the current sea level, or within grasslands that will become deserts, or within forested land that will become prone to fire - to resettle in places that are out of climatic risk, then I think you will have done everything that is reasonable.

Arguing about magnitude, detail, nuance - that does nothing to address the crisis. The empirical evidence is rock solid - humans are shifting the balance of GHGs in the atmosphere by burning fossil fuels. Changing GHG concentrations are associated with climate change. Climate change has the potential of causing people living in places that used to be able to support a viable population to not be able to live there anymore. So, they will migrate, or they will die. They won't choose to die, but if we don't allow them to migrate, we will have left them with no other choice.

Climate driven migration is not new - it's happened before and will happen again. This time, however, we know it is coming, and we can do something about it. If we do nothing about it, then we are fiddling while Rome burns.

This is complicated (or simplified, if you want to think about it that way) by a declining EROI in fossil carbon. We will cease to be able to maintain a growth economy by relying on fossil carbon within a generation. By default, we will choose to move away from carbon as our primary energy source, because other energy sources will provide a higher rate of return. We will still have half (or maybe a little more) of the fossil carbon that can be extracted in the ground when we decide to give up on carbon energy. I see nothing wrong with accelerating that timing to decrease the ultimate magnitude of the ecological impacts associated with excess CO2.

If we don't - if we assume business as usual until it isn't possible any more, there will end up being a contraction, if not collapse, of the world economy. Instead of 60 million ecological refuges, we would be dealing with 500 million economic ones. If you try to tell them they can't migrate, they will fight for their lives, and rivers will flow red.

Me, I don't spend much time trying to 'fix' climate change in one way or the other. I accept it is happening, and it is exacerbated by human activity. I stop there. My designs will always assume a low energy intensity future, and then the descendants of my clients will be pleasantly surprised if I'm wrong. Instead of being betrayed (again) by poor choices made by people who should have known better.

Douglas Nuttall All this moral appeal and calls to action are grossly premature. We do not have evidence to support any of these dangerous scenarios as being caused by CO2. Emmert 2012 has demonstrated that the heat flux into space is increased by higher CO2. This is a very strong piece of evidence against AGW, although i agree, it is not entirely convincing because we are not concerned about fluxes but net temperature in the troposphere. But it is bound to have a mitigating effect on CO2 induced warming in the troposphere. The crucial point is we may be targeting the wrong gas, and as such causing more harm while not dealing with the actual cause of the problem. I am sure you can appreciate the ecological cost of such a mistake.

Ok. I'll play along. There is convincing pre-historic evidence of an empirical relationship between sea levels, climate, and CO2. There are any number of anthrogenic atmospheric pollutants that could also be players. Are you aware of an equally strong empirical relationship that involves a different cause?

Lets step though this slower. There is climate change. It is rapid. The timing and magnitude is highly suggestive that it is primarily anthrogenic, and this view is supported by no small amount of science. If we do nothing at all to prevent the anthrogenic effects, there are going to be severe ecological, economic, and social impacts. If we do something about the right cause, there are going to be less severe ecological, economic, and social impacts, but it is likely too late to say there will be none. If we do something about the wrong cause, it will be not much better than doing nothing at all. It is very unlikely that it will be any worse.

So, in the absence of better evidence, the scientific consensus is to advise the world as a whole to stop burning fossil carbon. Its the prudent thing to do.

The economic impacts of ceasing carbon emissions will be felt in about 25 years, as the EROI drops to a point that can't support a growth economy. We could choose to adapt faster than that, and figure out how to have a growth economy without fossil carbon. That may not make any difference on the ecological impacts - particularly if you are right and we're not approaching the climate change issue from the right direction. But it will vastly mitigate the economic impacts - potentially eliminate them altogether.

So maybe, as you imply, there are other causes of climate change, but eliminating carbon emissions will not cause any harm ecologically (CO2 is already out of the range of 'normal' for many millions of years) and it will mitigate harm economically. I don't mind a bit if we all transition away from carbon fuels while we try to figure out what is really causing climate change. I don't see any ecological cost for moving away from fossil carbon, and the economic ones we are going to bear anyway. So, I do not 'appreciate the cost of such a mistake.' Sounds like it's completely neutral at worst, and net positive at best. I'll take that bet, then.

Douglas Nuttall CO2 stimulates growth of plants, it is crucial in time where human population cuts out more and more vegetation. You may be familiar with this report: https://www.nasa.gov/feature/goddard/2016/carbon-dioxide-fertilization-greening-earth. So unnecessary reduction would be harmful.

The economic cost of moving away from fossil fuels is immense, perhaps prohibitive in the short term, as China has found out. All these solar plants in the deserts and no transmissions capacity to utilise it in the industrial centres. Solar power showing up only in statistics as “produced” and then going straight into the ground. No wonder they are currently developing coal power capacity equal to that the present capacity of the USA: https://culturalanalysis.net/2018/11/03/chinas-energy-gambit/ Imagine the infrastructure required to charge all the cars, if all converted to DC.

Now i am not so sure about warming. The data is being adjusted in ways which dont make sense. The entire trend seems to be artificial. We had the Climate Gate showing intention to deceive. 2019 was back at the 1981-2010 average in the USA according to NOAA: https://www.researchgate.net/deref/https%3A%2F%2Fwww.ncdc.noaa.gov%2Ftemp-and-precip%2Fnational-temperature-index%2Ftime-series%3Fdatasets%255B%255D%3Dclimdiv%26parameter%3Danom-tavg%26time_scale%3D12mo%26begyear%3D1981%26endyear%3D2019%26month%3D6, the Antarctic ice is back at long term average also. It’s hard to know what is the truth on this fundamental point. But lets assume the warming is real for now.

All these issues aside, there is almost irrefutable, direct evidence that CO2 cannot be the driver of climat change, the following climate sensitivity study by Humlum et al. (2013): Article The phase relation between atmospheric carbon dioxide and gl...

The authors demonstrate, by analysing the official data-sets, that seasonal variations in the rate of change in the atmospheric concentration of CO2 have no measurable effect on the rate of change in global temperature; a result which is radically inconsistent with the net anthropogenic warming model. Another way, sensitivity of GMTA to CO2 is zero. This is a direct study, no modelling or abstract assumptions were required, just the actually observed rates of change. This is huge and so simple test of the popular hypothesis that it astounds me that nobody did this before or ever again. This alone is telling, that there is more involved here than commitment to science.

If not CO2 then what could cause warming? Perhaps the warming is faked by the data adjustments, perhaps it is a different greenhouse gas, perhaps it is changes in low cloud cover as some suggest, perhaps electromagnetic space phenomenon, perhaps something we have no understanding of. As i pointed out before all warming cycles in the paleohistoric past began on their own, at low CO2, and CO2 concentration followed thousands of years later, as per EPICA/VOSTOK. IPCC seems to rely only on inferences from correlation, but there is not even consistent correlation, and correlation is not even causation.

Ah, I'm sorry - I misunderstood. You were asking about empirical relationships, and you are arguing with science. Engineers get this messed up all the time. Manning's equation, as one example of gazillions, is empirical, and is reasonable for about 2.5 orders of magnitude of depth and 2.5 orders of magnitude of velocity. But it has no explanation of 'why', only 'what'.

Likewise, empirically, there is a relationship between climate, ocean levels, and CO2 levels. There is no explanation of 'why' - that's not how empirical relationships work. That relationship looks pretty tight, considering we're looking back in time for 400,000 years to build it. But it isn't 'science'.

For that, you need to talk to climate scientists, and ask about the actual science, not the empirical relationships. That's a much harder conversation to have, even if you have an open mind.

Generally, extraordinary claims (or ones that run counter to orthodoxy) require extraordinary evidence. If, as some claim, 97% of climate scientists agree that ACC is occurring, and the main driver right now is CO2 emissions, then your evidence against would have to be pretty significant.

Arguing that CO2 is good for plants won't cut it. O2 is good for people, too, but no one would advocate a 50% increase in concentration in a generation is good for anyone.

Not really.

Douglas Nuttall My comment about CO2 being good for plants was only relevant in context of your statement that there would be no harm in reducing it. but i agree this is a side question. Regarding the empirical relationship, we know that correlation is not causation, and in this case we do not even have consistent correlation. I understand that evidence of correlation can still be sound provided the anomalies were explained, but again, we are inevitably dealing here with complex science. Consider that the empirical case must also take into account second-order correlation; if the rates don’t correlate, this casts doubt on causal significance of the first order correlation, as per Humlum 2013 cited in my previous comment.

The wider debate and my interest is about this alleged causal relationship between CO2 and Temperature, supported by empirical evidence.

EDIT: What evidence do you rely on to conclude that 97% of climate scientists agree that CO2 drives global warming?

Apart from empirical evidence, natural evidence as can be seen today shows that the increase in human population, deforestation and industrialization caused the increase in the global warming as the natural sinks are being depleted daily.