Add this to the list of why deserts are awesome: they can suck a bunch of carbon dioxide out of the atmosphere.
For ten years, researchers in southern Nevada piped extra carbon dioxide into the Mojave Desert’s air. Their goal was to learn about the capacity of arid ecosystems to absorb carbon dioxide as we continue to burn fossils fuels. In their study published this week in journal Nature Climate Change, they discovered that when they suffused the air above research plots with carbon dioxide levels equivalent to those anticipated by 2050, plants still removed lots of carbon from the atmosphere.
Upon digging up the plots at the end of the experiment, researchers found that the areas living in a simulation of 2050’s carbon-rich atmosphere stored about 20 percent more carbon in the soil compared to untreated desert. That storage came from plants using carbon dioxide during photosynthesis, which they then pumped into the soil through their roots. It may not sound surprising that more carbon dioxide in the air leads to more of it stored in the soil, but there are limits to how much carbon ecosystems can absorb. And with scrappy shrubs instead of massive trees, it wasn't a given that the desert could take up quite so much.
And if arid and semi-arid ecosystems worldwide are as carbon-hungry as the Mojave, that’s good news. It means those dry lands, which cover about 47 percent of the non-ocean Earth, have a great potential to mop up the carbon dioxide we’re adding to the atmosphere. The study’s authors estimate that deserts and semi-arid places may absorb four to eight percent of global carbon emissions by 2045, assuming they all act like the Mojave did between 1999 and 2009. The researchers also estimate that deserts already account for 15 to 28 percent of the current land-based uptake of carbon emissions today.
Until now, scientists didn’t know the role deserts play in offsetting our fossil fuel emissions over multiple years. We already knew that of the 350 billion metric tons of carbon humans added to the atmosphere between 1959 and 2010, the land and ocean took up just over half of that. And we can measure how much goes into the ocean pretty readily. But since Earth’s ecosystems are so diverse and complex, it’s hard to keep track of the carbon we emit from burning fossil fuels once it’s absorbed by plants and stored in soils. Scientists know that forests, grasslands, and the Arctic are big carbon sinks, but beyond that the land-based carbon budget gets fuzzy.
That’s why over a decade ago, researchers kicked off this carbon enhancement experiment and 11 more in other locations, including forests, grasslands and agricultural fields, to simulate our future atmosphere’s carbon dioxide levels and to learn how ecosystems will deal with them over the long term. Will ecosystems absorb the carbon, or emit it, and why? A key benefit to answering these questions is that they will help improve climate projections. For example, if deserts expand, knowing their carbon storage capacity will help explain what that expansion means for warming; and whether it's an overall gain or loss for the planet may depend on the ecosystems they replace. “To effectively understand future changes we need to get a handle of what’s going on with individual components," says study co-author Dave Evans, an ecologist based at Eastern Washington University. “That’s where this study contributes; it gives the first results from a long-term experiment on arid systems.”
There’s more the authors would like to know, like what happens to carbon storage in the desert when temperature increase, or nitrogen levels go up because our industrial activities have added it to the atmosphere. Evans hopes that studies in other desert regions will add more detail to the information he and his collaborators uncovered.
For me, this study brought up another big unknown: What happens to the desert’s appetite for carbon storage when the soil is disturbed? For example, could we be trading the desert's natural carbon storage in exchange for renewable energy, as the Bureau of Land Management oversees industrial-scale solar development in the Mojave? For now, all we know is that the undisturbed Mojave Desert is pretty good at sucking carbon dioxide out of the atmosphere. How land use decisions affect that new-found capacity remains another climate mystery for now.
Sarah Jane Keller is a High Country News correspondent based in Bozeman, Mont. She tweets @sjanekeller.