A week after we were told that India is heading towards a record wheat harvest, an Economist sob story claims that trace amounts of CO2 make it much harder to grow wheat there

A special report on feeding the world: No easy fix | The Economist

Global warming upsets the world’s water cycle, increases the burden of pests, desiccates soil and reduces yields. In 2010 the world got an unpleasant taste of what climate change might bring.
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But a lot else is happening. An increase of 2°C in global temperatures, says Hans-Joachim Braun, the head of CIMMYT’s wheat programme, could cause a 20% fall in wheat yields. This would exceed any possible gains from warming in areas currently too cold to grow crops and would also offset the benefits of rising carbon-dioxide concentrations. Plants eat CO2, so if there is more of it in the atmosphere, photosynthesis should increase and yields rise. But no one knows by how much.
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When the International Food Policy Research Institute (IFPRI) tried to work out the impacts of climate change on the main cereal crops, almost all its results suggested that yields in 2050 are likely to be lower than they were in 2000, sometimes much lower. Almost half the forecasts showed yield reductions of 9-18% by 2050. One came up with a drop in rainfed-maize yields of 30%. The most vulnerable crop turned out to be wheat, with the largest losses forecast in developing countries. The Indo-Gangetic plain, home to a seventh of mankind and purveyor of a fifth of the world’s wheat, is likely to be especially hard hit.

Feb. 2011: Overheated world update: India heading towards record wheat crop

India, the world's second biggest wheat producer after China, is heading towards harvesting a record 81.47 million tonnes of the produce in the 2010-11 crop year.