The United States and many other heavily populated countries face a growing threat of severe and prolonged（延长的，拖延的） drought in coming decades, according to results of a new study by National Center for Atmospheric Research (NCAR) scientist Aiguo Dai. The detailed analysis concludes that warming temperatures associated with climate change will likely create increasingly dry conditions across much of the globe in the next 30 years.

The drought may reach a scale in some regions by the end of the century that has rarely, if ever, been observed in modern times.

Using an ensemble（全体，总效果） of 22 computer climate models and a comprehensive index of drought conditions, as well as analyses of previously published studies, the paper reports that by the 2030s, dryness is likely to increase substantially across most of the Western Hemisphere, along with large parts of Eurasia, Africa, and Australia.

By later this century, many of the world's most densely populated regions will be threatened with severe drought conditions.

In contrast, higher-latitude regions from Alaska to Scandinavia are likely to become more moist（潮湿的） .

Dai cautioned that the findings are based on the best current projections of greenhouse gas emissions.

What happens in coming decades will depend on many factors, including actual future emissions of greenhouse gases as well as natural climate cycles such as El Niño.

The new findings appear this week as part of a longer review article in Wiley Interdisciplinary（各学科间的） Reviews: Climate Change. The study was supported by the National Science Foundation (NSF), NCAR's sponsor.

"This research does an excellent job of placing future warming-induced drought in the context of the historical drought record," says Eric DeWeaver, program director in NSF's Division of Atmospheric and Geospace Sciences, which funds NCAR.

"The work argues credibly that the worst consequences of global warming may come in the form of reductions（减少，缩小） in water resources."

While regional climate projections are less certain than those for the globe as a whole, Dai's study indicates that most of the western two-thirds of the United States will be significantly drier by the 2030s.

Large parts of the nation may face an increasing risk of extreme drought during the century.

"We are facing the possibility of widespread drought in the coming decades, but this has yet to be fully recognized by both the public and the climate change research community," Dai says. "If the projections in this study come even close to being realized, the consequences for society worldwide will be enormous."