Are Deserts Hidden Carbon Sinks?

Gobi DesertClimate scientists are beginning to suspect that deserts (PDF) may be "hidden" carbon sinks.

Much like dark matter in space, these vast stretches of nothingness, comprising 35 percent of the earth's surface, may not be dead zones after all, but may in fact be quietly sequestering as much as 5 billion tons of carbon dioxide every year.

Though no one yet knows what purpose dark matter serves, except to keep the planets from bumping into each other, climatologists have recently identified the process whereby deserts absorb carbon dioxide. It seems that deserts, with their billions of grains of sand, create a vast, permeable surface which allows carbon dioxide to mingle readily with alkaline soils (the soil type most common to deserts) to produce carbonates.

Scientists have been struggling since the middle of the last century to balance human carbon dioxide production with natural carbon sequestration by forests and oceans, and the remaining carbon dioxide left in the atmosphere. Clearly, some of the carbon dioxide is missing, given the rise in emissions over the last 14 years (from 359 parts per million in 1994 to more than 384 parts per million at present).

How, scientists ask, can we be producing so many more emissions and not seeing an exponential rise in atmospheric carbon dioxide levels? Particularly as forests are declining worldwide, and oceans have almost reached their maximum carbon dioxide storage capacity?  

The answer may lie in desert sequestration, a possibility that first presented when Chinese plant ecophysiologist Li Yan began measuring carbon dioxide in the Gubantonggut Desert. To Li's surprise, the desert was soaking up carbon dioxide at night, a hitherto unobserved or unreported phenomenon that led Li to a surprising culprit; alkaline desert soils.

At first, Li thought it was something wrong with his equipment. The vegetation, thin to the point of invisibility, clearly wasn't acting as a carbon sink, nor were there any nearby land or water formations that could account for the disappearance.

Mojave DesertWhen scientists like Lynn Fenstermaker, of the Desert Research Institute (DRI) in Nevada, discovered a similar pattern while working in the Nevada portion of the Mojave Desert, scientists around the world began to reassess the carbon sequestration model of earth.

If the results of the two studies are an accurate reflection of unknown processes, the discovery would indicate that deserts are capturing at least half the earth's fossil-fuel related carbon emissions. But it's too soon to throw a party or rescue that 1999 gas-guzzler in your garage, because some scientists remain unconvinced, pointing out that carbon fluctuations are difficult to measure and only continuous global desert readings at numerous locations will prove these two experiments representative rather than anomalous.

One such dissenter, William Schlesinger (a biogeochemist at the Cary Institute of Ecosystem Studies in Millbrook, New York) - who first examined desert carbon fluxes in the 1980s, says he would be "hugely surprised" if the evidence turns out to be true. What is particularly disturbing, Schlesinger says, is an absence of the amounts of carbonate that would indicate this process is fact rather than fiction.

In fact, while the carbon dioxide may be forming carbonates at night, it's possible the process may reverse itself in the daytime, when temperatures rise. In that case, suggests DRI soil chemist Giles Marion, Li's studies are telling only half the story.

Li concedes this is possible, but notes that that his daytime measurements of carbon dioxide flux did not negate the nighttime uptake. Other scientists argue that absorption alone can't explain the phenomenal uptake in the Mojave, where instruments show a carbon sequestration rate of 100 grams per square meter every year from 2005 to 2007. Compared to carbon sequestration in a Southern pine forest in the U.S, at about 220 grams per square meter per year - or carbon capture in a Finnish forest at about 400 grams per meter - this is an outstanding carbon capture model for terrain with little or no vegetation.

Jayne Belnap, A USGS (U.S. Geological Survey) scientist working at the Canyonlands Research Station in Moab, Utah agrees with Schlesinger, reporting on her own and other studies in southern Utah deserts with similarly carbonaceous soil types.

"We do not see any such results," Belnap insists.

In the absence of any identifiable factors that would explain Li's and Fenstermaker's results, scientists worldwide are adopting a wait-and-see attitude, suggesting further investigation but not yet willing to put all their eggs in one basket where the fate of earth is concerned.

If the flux findings are a fluke, environmental scientists will have to find a way to deal with all the carbon dioxide currently being released by Arctic melting, which they estimate may effectively double the existing carbon dioxide burden and dump tons of methane (another global warming gas) into the mix as well. 

2 comments

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Siegfried Fleischer (anonymous)

A Swedish radio commentator referred to the desert carbon sink in Nevada. Very interesting. Chemoautotrophic CO2 uptake may be the most possible explanation. Please read S. Fleischer & I. Bouse, Tellus 60B, p 782-786, 2008. And please give me your comment. Best wishes S. Fleischer, Halmstad Univ., Sweden.

Written in November 2009

Thank you, Professor Fleischer. I'm unable to purchase the article, but from what I understand of chemoautotrophic CO2 uptake, I'm sure you are correct. And, as you also point out, nitrogen loading might impact that sequestration negatively.

Written in November 2009

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  • Posted on Nov. 11, 2008. Listed in:

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