Jun 29 2009, 10:00AM
Daily Chart: What Global Warming Will Do To Global Agriculture
Since I think a lot of this discussion of global and national GDP obscures the most worrying cost of global warming -- namely, the vast impact climate change will have on developing nations -- I thought I would dig up some charts on global warming and global agriculture production. The most rigorous study on this subject that I know of is William Cline's Global Warming and Agriculture. (You can actually download the chapters from that link.)
The basic points of Cline's book are that, by the end of the 21st century, (1) climate change will lead to a slight decline in global agricultural productivity; and (2) climate change will lead to a giant decline in agricultural productivity in Africa, South America and India.
Here are two charts that sum this up. The first is the change in agricultural productivity (by 2080) taking into account the potential benefits of "carbon fertilization" (the increase in yield that occurs in a carbon rich environment*):
Not hard to see why Russia and China might find a climate bill unappetizing. (Likewise the good people of Minnesota.) Here is the change in agricultural productivity without assuming benefits from carbon fertilization:
As a sidenote, I think it's important to recognize that deep brick color falling over most of Africa, South Asia and Latin America -- all places where agricultural productivity will fall by more than 25% -- actually hides big differences. For example, Cline reports that the southern regions of India would experience potential output declines of 30-35%, while northern regions would experience declines of 60%.
*Quick note about this: The effects of carbon fertilization are very uncertain, and depend crucially on the availability of other resources -- water for irrigation, say -- that will also be affected by global warming. I'm not in a position to parse the various bits of evidence. But it's worth noting that, even if carbon fertilization yields large benefits, Cline estimates a decline in global agricultural productivity.
We can use models to put numbers on the predictions of a theory. But the model doesn't add anything to the theory. If the theory is wrong, you just get a pretty map of a wrong answer.
This is not to disparage all climate science. But recognize that our theories of climate are not some neat little formula like gravity. They are a mess of partial models of some aspects of climate, mixed with constants assumed from history, and plain old guesses.
These models have no track record, so they can't be evaluated externally. You are just taking the word of researchers. None of these graphs even show estimated error factors. To be honest, you'd want to see a range from high to low based on uncertainties in the model and the source data. And those uncertainties would be very hard to estimate in the first place, since who knows if the model is any good until it has a track record?
Models are constructed on "past future" data; they may not be fully accurate heading forward, but they have been tested within experimental constraints. If you'd like to dismiss those theories, maybe you should address them in the papers where they're published.
As a meteorologist, it is obvious to me that climate science is in it's infancy. Very little skill has been shown in the climate forecasts. The IPCC forecasts are now below the 95% confidence interval...in other words...the IPCC was 95% sure that it would be warmer now than it is. The earth hasn't warmed in 10 years and is in a 7 year cooling trend.
When you then take a forecast with virtually no real world skill and then start building new models with dubious assumptions on top of it with a 90 year time frame, you end up with a total pile of worthless junk such as this study.
Also, consider that billions of $$$ are now available for climate change research. If you tie your research to "Climate Change", suddenly it is much easier to get funding. If you publish something skeptical of the standard "climate change disaster", then you will be severely frowned upon by your peers for not being a friend of the earth and for killing the goose that is laying the golden egg...ie research funding.
Be skeptical. Be very skeptical. After all, that's what scientists are supposed to be.
I am glad to see that you included a map without the very tenuously evidenced "carbon fertilization." My training is in ecology and evolutionary biology, and there have been several studies on this, including one particularly thorough one that included whole sections of forest isolated and given years of raised atmospheric carbon to utilize, with very little positive effects. The issue is that carbon, particularly atmospheric carbon, is almost never the limiting nutrient in any major biome. Every study I have viewed shows at best a short initial increase of productivity that can't be sustained as some other limiting nutrient (calcium and potassium in your particular neck of the woods) becomes the new regulator of plant growth. Those who delude themselves into thinking that a very slight percentage increase in CO2 in the atmosphere will have anything like the effects your mapmaker posits do so with virtually no science to back themselves up. I am actually at a loss where they could get the idea that carbon fertilization could even make even a moderate impact.
As I think about it, there may be some agriculture methods that leave the soil so depleted of carbon that are far outside my area of expertise, but this would be the only way I can dream up to allow this. If anyone with that particular expertise is reading this, I would love to hear if this is the case.
I would also like to add to the discussion above that I know little of computer climate models, but every species that I am aware of being studied heavily is showing range changes consistent with warming already occurring (read about sugar maples in the NE US if you want a local example Andrew, my current home state of CT has a maple syrup industry that is already hurting badly even as forests are actually close to having recolonized the state). Species are either moving up in latitude (NH) or higher in altitude at rates plainly observable. To disagree with climate change being hard science, there are far more than computer models to tangle with (I myself doubt their accuracy, but there's no denying arctic ice disappearing or biome migration that I can understand).
"We can use models to put numbers on the predictions of a theory. But the model doesn't add anything to the theory. If the theory is wrong, you just get a pretty map of a wrong answer."
I agree, but you forget that every model is 'wrong'. Models are only useful insofar as they help us achieve some goal. The only perfect model is reality itself.
We must always consider the possibility that our model is right, in this case.
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(Editor Chefe - Aprenda dinheiro na internet conosco!)