A new NASA study is predicting the occurrence of severe "megadroughts" across the United States in the second half of this century, that are set to be more extreme and prolonged than any droughts that have taken place in the region for the past 1,000 years. According to the study, one of the key driving forces behind the devastating droughts will be the prolific creation of human-produced greenhouse gasses.

The study made use of several climate models including one spearheaded by NASA, and is the first of its kind to use historical data stretching back as far as 1,000 years. Most modern drought indicators only use data from around 100 years in the past, however NASA's most recent study was able to draw on environmental conditions prevailing in the distant past by making use of a well established tree-ring database.

Using this wealth of natural information, the team were able to pinpoint drought events by observing the spaces between rings in tree trunks, a process known as dendrochronology. Some trees grow significantly more during years with prevalent rainfall, producing wider spacing between the rings, and have stunted growth during periods of drought, creating closer rings. By observing ring patterns in the same species of tree during modern droughts, the study was able to produce accurate drought maps for the last 1,000 years. This allowed climate scientists to examine the big picture, taking into account drought cycles in a much longer context.

30-cm (11.8-in)-deep moisture projection based on NASA's moderate carbon emission scenario in the year 2095 (Image: NASA's Goddard Space Flight Center)

"Natural droughts like the 1930s Dust Bowl and the current drought in the Southwest have historically lasted maybe a decade or a little less," states Ben Cook, lead author of the study and climate scientist at NASA's Goddard Institute for Space Studies and the Lamont-Doherty Earth Observatory at Columbia University, New York. "What these results are saying is we're going to get a drought similar to those events, but it is probably going to last at least 30 to 35 years."

According to the study, the severity of future droughts will be determined by humanity's approach to carbon emissions in the coming years. Cook and his team state that with the current levels of greenhouse gasses in Earth's atmosphere, the possibility of a drought lasting around 30 years sits at around 12 percent. If carbon emissions level off around 2050, this figure rises to 60 percent. In the event of man-made carbon emissions continuing to rise at the current pace, there is a harrowing 80 percent chance of a megadrought engulfing the Southwest and Central Plains from 2050 to 2099.

Droughts of this magnitude and severity would place the agricultural capabilities of the US under greater stress at a time when there is already set to be significant food shortages on a global scale, in part thanks to the effects of global warming.

The video below courtesy of NASA highlights the key points made by the study.

Source: NASA

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