sexta-feira, 23 de maio de 2014

Dust Bowl Days: Will We Cut Carbon Pollution Fast Enough To Prevent Permanent Droughts?

By Joe Romm on May 22, 2014
Large parts of the Southwest are drier than they were during the 1930s Dust Bowl. And the latest science says unrestricted carbon pollution will make this a near-permanent situation post-2050 in a growing portion of this country and around the world — for a thousand years or more!
Earlier this month, the U.S. Drought Monitor warned that “devastatingly dry, dusty, windy conditions on the southern Great Plains fueled concerns of a ‘New Dust Bowl’.” The epicenter of the 1930s Dust Bowl was where Kansas, Colorado, New Mexico and the panhandles of Texas and Oklahoma come together.
The National Weather Service has measured rain over the last three and a half years and reported that parts of those states have “had less rain than what fell during a similar period in the 1930s.” Amarillo, Texas is 10 percent drier.
Already this year, Boise City, in Oklahoma’s panhandle, has endured ten dust storms with gusts more than 50 miles per hour. And that is despite vastly superior agricultural practices than we had 70 years ago. As NOAA’s discussion of “The Dust Bowl Drought” explained:
The “dust bowl” effect was caused by sustained drought conditions compounded by years of land management practices that left topsoil susceptible to the forces of the wind.
Now human-caused climate change is kicking in, heating up and drying out the region. I’ve written many times about how temperature increase, even without a precipitation decrease, will lead to more drought. That is because it dries up the soil, and reduces the late spring snowpack that many Western states need as a water reservoir during the summer dry season. And remember, the Earth has warmed only a bit more than 1°F since the catastrophic Dust Bowl — and we are poised to warm perhaps 10 times that this century if we stay anywhere near our current greenhouse gas emissions path.
But climate science makes very clear that precipitation is very likely to decrease in the semiarid regions near the subtropical dry zones. Last week I wrote about a NOAA-led study that found “the location where tropical cyclones reach maximum intensity has been shifting toward the poles” at roughly 35 miles per decade. The lead author Jim Kossin explained, “The rate at which tropical cyclones are moving toward the poles is consistent with the observed rates of tropical expansion.”
Interestingly, the authors noted that their analysis of the latitude of maximum intensity “reveals a significant change point in 1996″ while the expansion of the tropics, “as measured by the meridional extent of the tropical Hadley circulation,” displayed “a step change in the late 1990s.”
The expansion of the tropics should be of great interest to everyone because it is a long-standing prediction of climate science and because it is directly linked to the fact that “the world’s subtropical dry zones are shifting towards the poles,” which, as one 2012 study found, resulted “in sharp rainfall declines during April and May in regions such as southern Australia.”
The expansion of the tropics is thus directly related to Dust-Bowlification, as I noted in my 2012 Nature piece, “The Next Dust Bowl.”
Here is a map of the subtropics (in yellow):
The subtropics

As Wikipedia notes, “A great portion of the world’s deserts are located within the subtropics.” Not all of the subtropics are deserts because “Areas bordering warm oceans are prone to locally heavy rainfall from tropical cyclones, which can contribute a significant percentage of the annual rainfall.”

Here is a simple illustration of the atmospheric dynamics that make so much of the subtropics into deserts.

Many of these regions are expanding and drying out already due to global warming (see “NOAA: Human-Caused Climate Change Already a Major Factor in More Frequent Mediterranean Droughts”). A detailed literature review of “Subtropical drying and tropical expansion” can be found here. In 2012, Climate Progress explained that “Manmade Pollutants May Be Driving Earth’s Tropical Belt Expansion And Subtropical Dust-Bowlification.”
Finally, as we reported earlier this month, the National Climate Assessment describes the stark choice we face on Dust-Bowlification:

Read in full at ThinkProgress

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