On the water frontOcean changes may trigger U.S. megadrought

Published 16 June 2008

From AD 800 to 1250 the North American continent suffered from an exceedingly dry period; experts build climate model which shows that the warming of the oceans may lead to another long parched period — what they call “megadrought”

Resdients of California will hope the drought in their state will not 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 °C would reduce the occurrence of winter storms. Meanwhile, effects of changes in the Atlantic would strike mainly in summer: warming of 1 °C would reduce the transport of moisture to the Great Plains of the central United States and western parts of the continent. When both these effects occur together, North America suffers a megadrought, says Feng. Though the occurrence of such droughts is normal, Feng warns that global warming may hasten their arrival. Similar ocean temperatures and warm climes coincided with the megadrought of AD 800 to 1250. 

-read more in Song Feng et al., “Atlantic and Pacific SST Influences on Medieval Drought in North America Simulated by the Community Atmospheric Model,” Journal of Geophysical Research 113 (2008), D11101, doi:10.1029/2007JD009347