Mojave Desert
April 7, 2014

Arid Regions Absorb Unexpectedly Large Amounts Of Atmospheric CO2

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redOrbit Staff & Wire Reports - Your Universe Online

Arid regions absorb an unexpectedly large amount of atmospheric carbon, according to the results of a 10-year research project in which scientists exposed the Mojave Desert to CO2 levels similar to those expected in 2050.

The discovery, which appears in the journal Nature Climate Change, will give experts a better grasp on the earth’s carbon budget. The carbon budget is the amount of the element that remains in the atmosphere in the form of carbon dioxide and contributes to global warming, as well as the quantity that winds up being stored in the land or the oceans in other carbon-containing forms, the authors explained.

“It has pointed out the importance of these arid ecosystems,” R. David Evans, a professor of biological sciences at Washington State University, said in a statement. “They are a major sink for atmospheric carbon dioxide, so as CO2 levels go up, they'll increase their uptake of CO2 from the atmosphere. They'll help take up some of that excess CO2 going into the atmosphere. They can't take it all up, but they'll help.”

Arid regions, which comprise a wide band at 30 degrees north and south latitude, receive less than 10 inches of rain each year. When combined with semi-arid areas, or regions which receive less than 20 inches of rain annually, they account for roughly half of the planet’s land surface.

Forest soils hold more carbon per square foot because they have more organic matter, but because arid regions cover such a larger amount of area, they can have an outsized role in the Earth’s carbon budget, the researchers said. As such, they could drastically impact how much the Earth warms as atmospheric greenhouse gases accumulate.

During their decade of work in the Mojave Desert, Evans and his colleagues removed soil and plants down to one meter deep, and then measured the amount of carbon that was absorbed. The study takes a look at one of the mysteries surrounding global warming: How much of the increasing amount of CO2 in the Earth’s atmosphere is being absorbed or released by land-based ecosystems?

The team worked at the Nevada National Security Site and marked off nine octagonal plots about 75 feet in diameter. They used PVC pipes to blow air containing current CO2 concentration levels of 30 parts-per-million (ppm) over three plots, while three received no extra air and three were exposed to concentrations of 550 ppm, which is the amount of carbon dioxide anticipated for the year 2050.

Thanks to a special chemical fingerprint that could be detected while the soil, plants and other biomass were analyzed, experts at the WSU Stable Isotope Core Laboratory found that arid lands could increase the carbon uptake enough to eventually account for 15 to 28 percent of the amount currently being absorbed by land surfaces. Overall, rising CO2 levels could increase those uptake levels to account for four to eight percent of current emissions.

While the study did not account for possible changes in precipitation levels, warming temperatures or other possible climate change-related variables, Evans said that he was “surprised at the magnitude of the carbon gain, that we were able to detect it after 10 years, because 10 years isn't very long in the life of an ecosystem.”

The project was funded by the US Department of Energy's Terrestrial Carbon Processes Program and the National Science Foundation's Ecosystem Studies Program was the brainchild of scientists working at universities in Las Vegas and Reno, Nevada. Researchers from the University of Idaho, Northern Arizona University, Arizona State University and Colorado State University were also involved in the investigation.

Image 2 (below): Mojave Desert plots like this see from a radio-controlled helicopter showed researchers that arid areas can absorb unexpected amounts of atmospheric carbon. Credit: Desert Research Institute/ University of Nevada at Las Vegas