Climate change curbs crops

http://www.nature.com/news/2011/110505/full/news.2011.268.html?s=news_rss

The study notes that the United States — which produces about 40% of the world's soya and maize — has so far been shielded from yield declines because its crop-growing regions haven't warmed in summer over the past 30 years, perhaps because of natural variability or the cooling counter-effect of aerosols.