Now a team in Germany has, for the first time, investigated the robustness of permafrost carbon dynamics against climate change, taking into account changes in vegetation distribution. They found that, while in the short term vegetation will store carbon, in the long term the thawing permafrost is bad news for carbon-dioxide concentrations in the atmosphere.

"In our simulations, the permafrost zone loses its capacity to sequester carbon under almost all considered levels of global warming," said Sibyll Schaphoff from the Potsdam Institute for Climate Impact Research, Germany. "The current sink will be amplified until 2050 but already around 2080 it will diminish or even turn into a source in 2100. Only for the 3.0 K global-mean-temperature-increase scenario does the permafrost zone still constitute a small sink."

Schaphoff and her colleagues used the Dynamic Global Vegetation Model LPJmL that simulates plant physiological and ecological processes and includes a newly developed discrete-layer energy-balance permafrost module and a vertical carbon distribution within the soil layer. The model is able to reproduce the interactions between vegetation and soil-carbon dynamics as well as to simulate dynamic permafrost changes resulting from changes in the climate.

The team found that the initial simulated net uptake of carbon may continue for some decades of warming. But once the turning point is reached, if carbon release exceeds the uptake, carbon is lost irreversibly from the system and cannot be compensated for by increasing vegetation carbon input. Although plant growth and subsequent input of organic matter may increase under global warming, even larger amounts of old soil carbon may be released into the atmosphere as temperatures increase. Those soil-carbon pools currently decompose very slowly and are strongly influenced by the temperature increase in the permafrost zone.

"This response is likely to continue over centuries and our research has highlighted that when modelling permafrost thawing, it is important to take vegetation feedback and long-time scales into account," Schaphoff told environmentalresearchweb.

The scientists reported their work in Environmental Research Letters (ERL).

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