"Climate change could reduce key harvests in China by a fifth if the gloomiest scenarios prove true, according to a study on Wednesday. ... Nationally, heatwaves have become more common, the number of cold days has fallen sharply and glaciers that are vital river feeders are in retreat, they say. The last century was the warmest period since 1600 and the country's seven warmest years have all occurred in the past decade. Climate extremes included droughts which hit the country in the 1960s, the late 1970s, early 1980s, the 1990s and in northeastern China in the last decade."