Rising atmospheric carbon could heighten ‘megadrought’ risk, study finds

If you remember (or even if you don’t) in “Climatological shift, cliff and other choice thoughts,” I insisted: “Whether one identifies oneself as a climate-change denier or climate-change believer there is no denying the climatological ‘cliff’ and ‘shift’ ideas.”

Elaborating farther, I explained, “There is no question … there exists in this existence the notion of ‘climatological cliff.’ It’s indisputable. And there is incontrovertible evidence that such was once overshot. Think ‘ice age.’ Not as drastic but still profound is the notion of ‘climatological shift.’ What this implies is meteorological change as in a marked change in climatic conditions or patterns.”

So, when I found the National Aeronautics and Space Administration (NASA) Feb. 12, 2015 “NASA Study Finds Carbon Emissions Could Dramatically Increase Risk of U.S. Megadroughts” news release, right away my curiosity was piqued.

Throughout history there have been droughts. According to NASA, in North America between 1100 and 1300, so-called “medieval-period” droughts occurred. Separating those from what the U.S. Southwest is experiencing today is that in the case of the former, some dry periods lasted as long as half a century.

Ben Cook, a climate scientist at the space agency’s Goddard Institute for Space Studies in addition to the Lamont-Doherty Earth Observatory at New York’s Columbia University, observed: “‘Natural droughts like the 1930s Dust Bowl and the current drought in the Southwest have historically lasted maybe a decade or a little less,’” although in the decades to come, drought durations could dramatically lengthen.

Cook, who headed a team in a recent NASA study, expressed that between 2050 and 2099, the likelihood of a megadrought lasting decades in both the Central Plains and Southwest regions, is 80 percent if, throughout the 21st century, the increase in greenhouse gas (GHG) emissions along current trajectories continue, that is, as I understand things. On the other hand, if, by 2050, the increase in GHGs is stemmed, Cook and study colleagues project the likelihood of megadrought to fall to north of 60 percent. Should either projection come to pass, what this could mean for the Central Plains and Southwest regions is nothing short of a significant reduction in the amount of precipitation and along with this heightened soil-moisture evaporation. Comparatively, at present, according to the study team leader, the likelihood of a drought lasting three decades or longer is 12 percent.

“The scientists analyzed a drought severity index and two soil moisture data sets from 17 climate models that were run for both emissions scenarios. The high emissions scenario projects the equivalent of an atmospheric carbon dioxide concentration of 1,370 parts per million (ppm) by 2100, while the moderate emissions scenario projects the equivalent of 650 ppm by 2100,” NASA in the release continued.

Furthermore, side-by-side comparisons of megadroughts of the past with 21st century computer-model projections reveal “both the moderate and business-as-usual emissions scenarios are drier, and the risk of droughts lasting 30 years or longer increases significantly,” adds NASA in the release.

Carbon dioxide concentration in the atmosphere, meanwhile, is presently 400 ppm.

For more on the NASA study, go here.

Image above: NASA

This post was last revised on May 9, 2020 @ 7:35 a.m. Pacific Daylight Time.

– Alan Kandel