Read more: “Climate change: It’s even worse than we thought“
Earlier this year, record harvests were predicted in the US, as farmers planted more to take advantage of rising prices. Instead, yields fell because of drought and record-breaking heat. The UK had a different problem: yields fell because of too much rain. With extreme weather hitting harvests in other areas, too, global food prices are soaring yet again.
That contrasts with the 2007 IPCC report, which predicted that if global temperatures rose 1.5 °C or more above pre-industrial levels, greater warmth and higher CO2 levels would increase yields, at least in temperate regions. .
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But it seems climate change is already having an adverse effect even though the world has warmed just 0.8 °C. Last year a team at Stanford University in California looked at global production of wheat, maize, rice and soybeans – crops that provide three-quarters of humanity’s calories – from 1980 to 2008. Based on what we know about how temperature, rainfall and CO2 levels affect growth, the analysis suggests that average yields are now . Without the fertilising effect of increased CO2, they would have been 3 per cent lower. “The negative effects outweighed the positive ones,” says lead author . The analysis doesn’t reflect the full effects of events such as floods, or the recent spate of extreme weather.
Wealthy countries should be able to compensate for these changes to some extent by altering what they grow and how they grow it, and by creating more heat-tolerant crop varieties. Indeed, they will have to: in 2008, the US National Bureau of Economic Research concluded that if the country’s farmers kept trying to grow corn, soybeans and cotton in the same areas, .
Keeping up with the pace of change will not be easy, though, and with dry regions projected to get drier, irrigation water could run out in places. There is also no easy way to protect field crops from extreme heat or rainfall. With the weather projected to become more variable in some regions, and perhaps globally (see “Climate downgrade: Extreme weather“), the biggest problem for the world’s farmers could be not knowing what to expect.
