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Big Trouble Ahead? Why the Forecasts for Food Production Could Be Entirely Wrong

It looks like scientists could have gotten the impacts of climate change on food supply wildly wrong.
 
 
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I believe we might have made a mistake: a mistake whose consequences, if I am right, would be hard to overstate. I think the forecasts for world food production could be entirely wrong.

Food prices are rising again, partly because of the damage done to crops in the northern hemisphere by ferocious weather. In the US, Russia and Ukraine, grain crops were clobbered by remarkable droughts. In parts of northern Europe, such as the UK, they were were pummelled by endless rain.

Even so, this is not, as a report in the Guardian claimed last week, “one of the worst global harvests in years”(1). It’s one of the best. World grain production last year was the highest on record; this year’s crop is just 2.6% smaller(2). The problem is that, thanks to the combination of a rising population and the immoral diversion of so much grain into animal feed and biofuels(3), a new record must be set every year. Though 2012’s is the third biggest global harvest in history (after 2011 and 2008)(4), this is also a year of food deficit, in which we will consume some 28 million tonnes more grain than farmers produced(5). If 2013’s harvest does not establish a new world record, the poor are in serious trouble.

So the question of how climate change might alter food production could not be more significant. It is also extremely hard to resolve, and relies on such daunting instruments as “multinomial endogenous switching regression models”(6). The problem is that there are so many factors involved. Will extra rainfall be cancelled out by extra evaporation? Will the fertilising effect of carbon dioxide be more powerful than the heat damage it causes? To what extent will farmers be able to adapt? Will new varieties of crops keep up with the changing weather?

But, to put it very broadly, the consensus is that climate change will hurt farmers in the tropics and help farmers in temperate countries. A famous paper published in 2005 concluded that if we follow the most extreme trajectory for greenhouse gas production (the one we happen to be on at the moment), global warming would raise harvests in the rich nations by 3% by the 2080s, and reduce them in the poor nations by 7%(7). This gives an overall reduction in the world’s food supply (by comparison to what would have happened without manmade climate change) of 5%.

Papers published since then support this conclusion: they foresee hard times for farmers in Africa and South Asia(8,9,10), but a bonanza for farmers in the colder parts of the world(11,12,13), whose yields will rise just as developing countries become less able to feed themselves. Climate change is likely to be devastating for many of the world’s poor. If farmers in developing countries can’t compete, both their income and their food security will decline, and the number of permanently malnourished people could rise. The nations in which they live, much of whose growth was supposed to have come from food production, will have to import more of their food from abroad. But in terms of gross commodity flows the models do not predict an insuperable problem.

So here’s where the issue arises. The models used by most of these papers forecast the effects of changes in averaged conditions. They take no account of extreme weather events(14,15). Fair enough: they’re complicated enough already. But what if changes in the size of the global harvest are determined less by average conditions than by the extremes?

This is what happened in 2012. This is what seems likely to happen in subsequent years. Here’s why. A paper this year by the world’s leading climate scientist James Hansen shows that the frequency of extremely hot events (such as the droughts which hammered the US and Russia) has risen by a factor of around 50 by comparison to the decades before 1980(16). Forty years ago, extreme summer heat typically affected between 0.1 and 0.2% of the globe. Today it scorches some 10%. “We can project with a high degree of confidence,” the paper warns, “that the area covered by extremely hot anomalies will continue to increase during the next few decades and even greater extremes will occur.” Yet these extremes do not feature in the standard models predicting changes in crop production.

 
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