Agricultural Production in a Warming World

More on global warming, this time from Conor Clarke, who links to William Cline's study Global Warming and Agriculture: Impact Estimates by Country. Clarke reproduces two maps from that study; this one shows "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"):



And this one shows the same without projecting carbon fertilization benefits:



Says Clarke:

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...

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%.

These maps, besides being delightfully Mondrianesque, illustrate beautifully (if that's the right word) the extent to which the business end of the global warming Howitzer is aimed squarely at the developing world (though the souther half of the UScould have some tough times ahead as well. The forecast for South Asia, which has enormous populations and is not that far removed from historically experiencing famine, and which could be among the most catastrophically inundated by rising seas starting near the end of the century, is especially distressing.

By contrast, under a favorable 'carbon fertilization' scenario much of the developed world actually comes out ahead (again, with the exception of the southern US, as well as much of Australia). China - around which the future track of global warming increasing hinges - also does rather well in the favorable scenario, and only somewhat poorly in the non-fertilization scenario. (By the way, as Clarke notes, "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... [But] even if carbon fertilization yields large benefits, Cline estimates a decline in global agricultural productivity.)

As always with climate projections, there is a lot of uncertainty involved here. Things might not turn out so bad in a given region, or they might turn out far worse; but it's worth noting that the consequences of global warming so far have tended to meet or exceed climate scientists' most pessimistic forecasts.