Deserts may come to the aid of humankind by helping to reduce global warming, say researchers. A new study has found that arid regions, among the biggest ecosystems on the planet, soak up unexpectedly large amounts of carbon. As levels of carbon dioxide (CO2) rise in the atmosphere, the deserts are likely to absorb more of the greenhouse gas and lower its impact.
"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," said Professor Dave Evans, from Washington State University in the US. 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."
A team led by Prof Evans conducted a 10-year study which involved exposing plots of California's Mojave desert to carbon dioxide levels expected in 2050. Soil and plants were then removed to a depth of one metre and measurements taken to see how much carbon was absorbed.
The results, published in the journal Nature Climate Change, found that increasing CO2 boosted activity of the rhizosphere, a microbe-rich area around plant roots. This, in turn, led to greater carbon uptake. The scientists calculated that arid lands may in future soak up enough carbon to account for between 4% and 8% of current emissions.
"I 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," said Prof Evans. Arid regions of the world receiving less than 10 inches of rain a year run in a wide band round the globe 30 degrees north and south of the equator.
Together with semi-arid areas, which receive less than 20 inches of rain, they account for nearly half the Earth's land surface. While forest soils rich in organic matter hold far more carbon per square foot, deserts cover such a large area that they have a significant impact on CO2. For the study, the scientists marked off nine octagonal plots about 75ft in diameter.
Air containing current CO2 concentrations of 380 parts-per-million was blown over three plots. Another three received no extra air while the remainder were exposed to the CO2 level expected in 2050, a concentration of 550 parts-per-million. A potential cause for concern is what might happen to arid ecosystems as the planet's population grows and spreads.
"Land is extremely valuable," said Prof Evans. "A lot of growth may occur in these areas that are fairly arid and we don't know what that's going to do then to the carbon budget of these systems."
