Faster permafrost melt than previously thought

4/08/2015 archaeological sites , carbon , climate change , Greenland , microbes , Northern Hemisphere , permafrost 0 Comments

Permafrost is soil at or below the freezing point of water 0 °C that stays frozen for two or more years. Permafrost comprises 24% of the land surface in the Northern Hemisphere and can be found at Arctic ocean shelves and floor. It contains large quantities of trapped greenhouse gases such as methane and carbon dioxide, and is usually regarded as a carbon sink. Researchers have become increasingly worried that with climate change large permafrost areas could start to thaw and ultimately melt, releasing massive amounts of carbon that would exacerbate global warming. 

A small team of scientists working in Greenland have now found evidence that as microbes become active in permafrost, they produce heat, which can increase the rate of permafrost melt. In their paper published in Nature Climate Change, Hollesen et al. (2015) describes computer simulations that showed possible impacts of microbe activation in permafrost areas. Previous attempts at predictions for permafrost melt through modeling are now looking like they will have to be revised. 

Suspecting that microbes in the soil might have an impact on warming permafrost, Hollesen et al. collected 21 samples of permafrost soil from six locations across Greenland. They then exposed the samples to different temperatures in a laboratory. By monitoring the heat production from microbes they were able to gather enough information to create a computer simulation. That simulation revealed that as global temperatures rise, a feedback loop occurs in permafrost areas. Heat causes melting which stimulates the microbes that start decomposing organic material, and producing heat, which adds to the increased temperatures, on and on until the permafrost melts, releasing massive amounts of carbon into the atmosphere far earlier than previous models have predicted. 

One immediate consequence of thawing permafrost in Greenland is the potential for destruction of unexcavated archeological findings. The National Museums of Denmark and Greenland have now started several projects where decomposing wooden artifacts and bones from the first people on Greenland will help identify areas most threatened. This is mainly happening because the average temperature has risen by 2-3°C in Greenland. Thawing of protective permafrost leads to archaeological material rotting because the amount of oxygen rises and the decomposition process accelerate. Other concerns are related to coastal erosion, resettlement and infrastructure damage.

More long-term consequences of permafrost thaw is of course increasing greenhouse gas concentration in the atmosphere, and in turn a warmer climate. Previous estimates have pointed to 120 ± 85 Gigatonne of carbon emissions from thawing permafrost by 2100, which could increase global temperatures by 0.29 ± 0.21 °C. However, we now know that permafrost starts to thaw much earlier than expected, so we need to start including this knowledge into climate models or we risk overshooting the 2°C warming limit. For example, the most recent knowledge on permafrost/carbon feedbacks are not included into IPCC climate projections.