Ocean changes may trigger US megadrought

CALIFORNIANS will hope the drought in their state won’t last as long as the parched period that afflicted North America from AD 800 to 1250. Even if it passes, global warming may yet hasten another 500-year “megadrought”.

Song Feng and colleagues at the University of Nebraska at Lincoln built a climate model to simulate the way changes in sea surface temperature of a few degrees in the Atlantic or Pacific can disrupt atmospheric circulation over North America. Such shifts caused droughts such as the 1930s Dust Bowl, which followed a cooling of the tropical Pacific.

The team found that the impact of these sea surface temperature changes differs by season. The effects of a change in the Pacific would hit mainly in winter: ocean cooling of 3