August 13, 2013 | In order to better understand the impact of carbon dioxide on Earth’s climate, scientists need to have a clear idea of what’s going on under their feet. That’s because the world’s soils store more carbon than the atmosphere and all the plants—combined.

To dig into this issue, a team of scientists led by Will Wieder, an NCAR postdoctoral fellow, have developed a computer modeling approach that focuses on microbial activity in soil. They published their findings in the July 28 issue of Nature Climate Change.

Soil microbes play an important role in the climate system because they eat carbon in soils and release it back to the atmosphere as they grow. Although tiny, they are so numerous that a single spoonful of soil often contains as many individual microbes as there are people living on Earth.

Wieder and his colleagues—Gordan Bonan at NCAR and Steve Allison at the University of California, Irvine—incorporated a model of global soil microbe activity into the land component of the NCAR-based Community Earth System Model. They found that future microbial activity may be greatly influenced by changes in temperature or plant productivity.

For example, higher temperatures can lead to accelerated activity by enzymes in the soil that release carbon into the atmosphere. Over this century, that could in theory lead to the release of some 300 petagrams (more than 330 billion tons) of carbon. But the higher temperatures may also reduce overall microbial biomass, offsetting the increase in enzyme activity. As the scientists explain in Nature Climate Change, “Consequently, global soil C [carbon] losses over the twenty-first century could be negligible, or massive.”

This range in results highlights how much researchers still have to learn about soils and their response to environmental change. The scientists say more research and improved modeling is needed to better understand the potential interactions between climate change and soil microbes.

“These are organisms we generally cannot see, but that can either help store carbon in soils or send it into the atmosphere where it contributes to climate change,” Wieder wrote in a recent online article. He adds, “So what that huge soil carbon pool might do matters a lot to projections of what our climate may look like in the future.”

William R. Wieder, Gordon B. Bonan, and Steven D. Allison, Global soil carbon projections are improved by modelling microbial processes. Nature Climate Change (2013) doi:10.1038/nclimate1951.  Published online 28 July 2013.

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