How Will Global Warming Affect Food  Production

Picture showing how global warming is affecting crops.

Most researchers believe that higher temperatures and droughts caused by climate change will depress crop yields in many places in the coming decades. But a recent consensus has emerged that rising atmospheric concentrations of carbon dioxide could come to the rescue. The gas thought to be behind global warming could also speed up photosynthesis, counteracting the negative effects of warming and even ushering in an era of bumper crops.

But Long told the two-day meeting on crops and future climate that this conclusion was a dangerous illusion. It was, he said, based on results from tests in gas chambers and small greenhouses known to be unreliable.

Long reported instead on the findings of four studies in the US, China and Japan that all test crops in open fields. In these Free-Air Concentration Enrichment experiments, gases such as CO₂ were piped into the air around plants - a world first.

Ozone-unfriendly

The FACE experiments showed that for all four of the world's main food crops - maize, rice, soybean and wheat - the real-world fertilization effect was only half as great as predicted by the contained experiments.

Meanwhile, in some FACE experiments, Long added a new variable not factored into previous studies. He puffed doses of ozone into the fields to simulate the expected rise in ozone smogs due to higher temperatures - and yields crashed. A 20% increase in ozone levels cut yields by 20%, he said.

Increases in ozone levels of this level are predicted for Europe, the US, China, India and much of the middle east by 2050. If Long's findings prove correct, even CO₂ fertilisation will not prevent the world's crop yields from declining by 10% to 15%.