Arid Lands May Help Stave Off Excess Carbon Emissions
Human activities during the past several years have led to the release of several greenhouse gases in the atmosphere. Chief among them: carbon dioxide (CO2). Still, the Earth has the ability to absorb large amounts of it into oceans and soil. And now, researchers have found from a 10-year study that arid areas are among the top carbon absorbers. The study will help scientists estimate the Earth's carbon budget and find out how much CO2 will remain in the atmosphere as a greenhouse gas, after the Earth's reservoirs have absorbed their limits.
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"It has pointed out the importance of these arid ecosystems," said R. Dave Evans, a Washington State University (WSU) professor of biological sciences, in a statement. He specializes in ecology and global change. "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."
Global warming experts still aren't sure how much CO2 is absorbed and released by land masses. The main goal of Evans' study was to determine that amount, as levels of CO2 in the air increase each day.
So, why are arid ecosystems so important for CO2 absorption? Arid and semi-arid areas get less than 20 inches of rain each year. They span widely across the north and south 30-degree latitudes in both hemispheres and comprise nearly half of the Earth's land surface. This makes them a major helper in absorbing excess CO2 from the atmosphere. Though forest soils can absorb more CO2, they account for only 31 percent of the world's surface area, far less than arid lands.
For the study, researchers chose nine octagonal plots about 75 feet in diameter. Three plots received air with 380 parts-per-million concentrations of CO2, the current CO2 levels. Three were exposed to concentrations of 550 parts per million, based on projected estimates of CO2 in the atmosphere in 2050, and three received no extra air. The CO2 was blown over the test plots through special PVC pipes running through the site, and had a specific chemical fingerprint that could be detected when soil, plants, and other biomass was analyzed.
In forest ecosystems, plants store CO2 in leaves and stems, while in arid ecosystems, the CO2 uptake is carried out in the plants' rhizosphere, an area around the roots rich in microorganisms.
So, the researchers cleared plants in the test plots and dug a meter into the soil to measure levels of CO2 absorbed.
They analyzed the soil and estimated that arid lands will eventually absorb 15 to 28 percent of all the carbon absorbed by landmasses - enough to account for four to eight percent of current emissions.
Even though the experiment did not account for factors like moisture levels or increased temperatures, which could be an after-effect of global warming, the scientists were able to detect a substantial amount of carbon in the samples in just one decade. This was surprising since, "10 years isn't very long in the life of an ecosystem", Evans said.
The scientists are optimistic that by 2050, arid lands will be huge players in CO2 absorption but are also worried about human encroachment on these lands, as populations grow. "Land is extremely valuable. A lot of growth may occur in these areas that are fairly arid and we don't know what that's going to do to the carbon budget of these systems."
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