http://www.nature.com/nclimate/journal/v7/n5/full/nclimate3262.html

Here we show that in each of the models, their present-day spatial distribution of permafrost and air temperature can be used to infer the sensitivity of permafrost to future global warming. Using the same approach for the observed permafrost distribution and air temperature, we estimate a sensitivity of permafrost area loss to global mean warming at stabilization of 4 (+1/-1.1) million km2  PER °C (1σ confidence), which is around 20% higher than previous studies. Our method facilitates an assessment for COP21 climate change targets11: if the climate is stabilized at 2 °C above pre-industrial levels, we estimate that the permafrost area would eventually be reduced by over 40%. Stabilizing at 1.5 °C rather than 2 °C would save approximately 2 million km2 of permafrost.

Researchers from the U.S. Geological Survey and key academic partners including the University of Colorado Boulder have quantified how rapidly ancient permafrost decomposes upon thawing and how much carbon dioxide is produced in the process.

Huge stores of organic carbon in permafrost soils -- frozen for hundreds to tens of thousands of years across high northern latitudes worldwide -- are currently isolated from the modern day carbon cycle. However, if thawed by changing climate conditions, wildfire, or other disturbances, this massive carbon reservoir could decompose and be emitted as the greenhouse gases carbon dioxide and methane, or be carried as dissolved organic carbon to streams and rivers.

“Many scientists worldwide are now investigating the complicated potential end results of thawing permafrost,” said Rob Striegl, USGS scientist and study co-author. “There are critical questions to consider, such as: How much of the stored permafrost carbon might thaw in a future climate? Where will it go? And, what are the consequences for our climate and our aquatic ecosystems?”

At a newly excavated tunnel operated by the U.S. Army Corps of Engineers near Fairbanks, Alaska, a research team from USGS, CU-Boulder and and Florida State University set out to determine how rapidly the dissolved organic carbon from ancient (about 35,000 years old) “yedoma” soils decomposes upon soil thaw and how much carbon dioxide is produced.

Yedoma is a distinct type of permafrost soil found across Alaska and Siberia that accounts for a significant portion of the permafrost soil carbon pool. These soils were deposited as wind-blown silts in the late Pleistocene age and froze soon after they were formed.

“It had previously been assumed that permafrost soil carbon this old was already degraded and not susceptible to rapid decomposition upon thaw,” said Kim Wickland, the USGS scientist who led the team.

The researchers found that more than half of the dissolved organic carbon in yedoma permafrost was decomposed within one week after thawing. About 50 percent of that carbon was converted to carbon dioxide, while the rest likely became microbial biomass.