Climate change wildcard: It’s hard to forecast how much carbon arctic soils may give up to the atmosphere with warming


From the North Forty News (Gary Raham):

In a recent Science News article (“Soil’s Hidden Secrets,” Jan. 28, 2012) Charles Petit said, “If the bank of carbon held in the world’s soils were to drop by just 0.3 percent, the release would equal a year’s worth of fossil fuel emissions.”

Soil hoards about three times the amount of carbon contained in the air and all above-ground vegetation combined, but it doesn’t just hold carbon like a laundry basket holds dirty socks. Soils form complex and varied ecosystems like the prairies, rain forests and coral reefs humans can more readily recognize. Soil scientists create color-coded soil type maps of the world that look like someone spilled a handful of confetti on an atlas. The problem is that these scientists sometimes have a hard time knowing just how and when different soils may play their carbon trump cards in a warming world.

In eastern Colorado, we walk on prairie soils. Such soils contain a layered mix of living and non-living components. Finely ground rocks, clay, sand and wind-blown debris (loess) form the bottom layer. The middle layers house a community of worms, mites, insects and microorganisms swimming in a sea of partially decayed organic matter invaded by networks of feathery roots and spider-web filaments of fungi. The remains of Ice Age mammoths and tigers mingle with those of the cattle and corn stalks of more recent grasslands. Billions of bacterial and fungal cells constantly work at breaking down a backlog of complex carbon molecules into climate-warming gases such as carbon dioxide…

“Biochar,” a clever term for charcoal created during fires in forests and grasslands, represents another wildcard in soil chemistry. Under certain conditions, biochar can sequester carbon in the soil for decades or centuries, but sometimes it can degrade within years and cycle the carbon into the atmosphere. Soil scientists, like Prof. M. Francesca Cotrufo at Colorado State University, work on ways to produce biochar for different purposes.

“Depending on the feedstock, temperature, and other conditions of pyrolysis (burning),” Cotrufo said, “we can make a biochar which is relatively easy to decompose and works best for soil fertility but not for carbon sequestration, as well as build a very recalcitrant biochar.”

The latter type keeps carbon compounds out of the air longer…

The soil that may hold the fate of the world’s climate in its black, carbon-rich depths lies in the Arctic. Scientists estimate that once permanently frozen Arctic soils contain 1.5 billion tons of carbon — about half of all the carbon contained in soils worldwide. As these soils warm and microbes fire up their engines, a torrent of greenhouse gases could tip the planet from the relatively icehouse conditions of today to the hothouse conditions of eons past.

More climate change coverage here and here.

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