Credit: NASA

Between 1978 and 2007, the number of summers in the southeastern US affected by drought or heavy rain doubled compared with the previous 30 years. This is because climate change is intensifying the Bermuda High, an area of high pressure that forms each summer over the Atlantic, suggests new research.

Wenhong Li at Duke University in Durham, North Carolina and colleagues analysed weather and climate data from 1948 and 20071. They found that the intensity of the Bermuda High increased, causing it to expand westward at a rate of 1.2 degrees longitude per decade. Variability in the western extent of the high-pressure system also increased by 47 per cent in the past 30 years compared with the previous three decades. Southward movement of the western ridge increases the likelihood of rain, whereas northward movement encourages drought.

When Li's team tried to recreate the observed change in the Bermuda High using models, only those forced by rising levels of greenhouse gas succeeded — suggesting that climate change is to blame. Future climate change will further increase the likelihood of drought or violent thunderstorms in the region, boosting soil erosion and reducing crop yields.