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Narrator: A new NASA study predicts that by the end of the 21st Century,

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the American Southwest and Great Plains are likely to experience

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longer and more severe droughts than at any other time

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in the last thousand years.

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Cook: So recent droughts like the ongoing drought in California or in the Southwest, or even

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historical droughts like the dustbowl in the 1930s. These are naturally-occurring droughts that

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typically last several years or sometimes almost a decade. In our projections what we're seeing

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is that with climate change, many of these types of droughts will likely last for

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20. 30. sometimes even 40 years. Even exceeding the duration of

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the long-term intense mega-droughts that characterized the really arid

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time period known as the Medieval Climate Anomaly.

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Narrator: So how can we peer into the planet’s future? Researchers combined natural

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harnessed the processing capabilities of powerful supercomputers.

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The scientists looked at a thousand years of tree ring data

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and compared those records with soil moisture data from

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17 different climate models. in order to extend this information into the future.

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The models all show a drier world thanks to increased temperatures

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from human induced climate change.

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Cook: These computer simulations, these climate models, really represent our best understand of

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the physics and the workings of the climate system. They're tested extensively against

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observations, and at the end of the day if we want to investigate future climate,

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they're really the only tool that we have to use.

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Narrator: How bad these droughts are likely to get has a lot to do with how much greenhouse gas emissions

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humans generate in coming years. Scientists looked at two different possibilities.

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First, a “business as usual” scenario where world-wide

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greenhouse gas emissions continue on their current course.

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In this case the future risk of lengthy droughts rises to 80%.

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lternatively, if the world were to take aggressive actions to reduce

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emissions, the models still show drying, but the trends will be less severe.

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In either scenario, droughts could

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potentially have major impacts in a region already facing water management concerns.

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Cook: These droughts really represent events that no

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in the history of the United States has ever had to deal with.

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And so even in the modern era droughts such as the ongoing droughts in California

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and the Southwest, these normal droughts act as major stresses

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on resources in the region, so we expect with these much longer droughts, it's going to be

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even more impactful and cause even more problems for agriculture

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and ecosystems in the region.

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