In a new study, researchers show that abrupt thaw could increase emissions by 40 percent.
The permafrost regions of the Arctic, often referred to as nature’s iceboxes, contain tremendous amounts of carbon, mainly in the form of animal and vegetable matter accumulated in frozen soils over millennia. Yet microorganisms break down this matter as soon as the frozen soil begins to thaw, releasing the harmful greenhouse gases methane and carbon dioxide. An international team of researchers has now determined that rapid thaw processes have a significant influence on the amount and types of gases released but were not considered in permafrost emission estimates so far. As they report in the journal Nature Geoscience, abrupt thaw processes, which are possible in ca. five percent of all Arctic permafrost landscapes, could potentially increase total emissions by 40 percent – a factor that has yet to be considered in current climate models.
Rapid thaw processes are already changing the landscapes and ecosystems of the Arctic, in particular when ice-rich permafrost thaws and the land surface collapses. Manifestations include collapsing permafrost peatlands, thaw slumps on hillslopes and the emergence of large sinks, in which rainwater and meltwater gathers, forming ponds and lakes. In turn, the surface of these so-called thermokarst lakes absorbs far more solar energy than the surrounding area. The heat stored in the water is then transferred to the frozen soil in a particularly effective manner – both under the bottom of the lake and below its banks, causing the surrounding permafrost to quickly thaw. The banks continuously collapse resulting in rapidly growing lakes. When this happens, it presents a golden opportunity for microorganisms to break down the animal and vegetable matter formerly trapped in the permafrost, producing greenhouse gases like methane and carbon dioxide in the process.
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