Permafrost that thaws abruptly releases twice as much greenhouse gas as when it thaws gradually. The problem is that much of the permafrost is now thawing much faster than had been expected. Okay, cause + effect = well, you can guess.
Permafrost, a perpetually frozen layer under the seasonally thawed surface layer of the ground, affects 18 million square kilometers at high latitudes or one quarter of all the exposed land in the Northern Hemisphere. Current estimates predict permafrost contains an estimated 1,500 petagrams of carbon, which is equivalent to 1.5 trillion metric tons of carbon.
Some 20% of the Arctic region has conditions conducive to abrupt thaw due to its ice-rich permafrost layer. Permafrost that abruptly thaws is a large emitter of carbon, including the release of carbon dioxide as well as methane, which is more potent as a greenhouse gas than carbon dioxide. That means that even though at any given time less than 5% of the Arctic permafrost region is likely to be experiencing abrupt thaw, their emissions will equal those of areas experiencing gradual thaw.
This abrupt thawing is "fast and dramatic, affecting landscapes in unprecedented ways," said Merritt Turetsky, director of the Institute of Arctic and Alpine Research (INSTAAR) at CU Boulder and lead author of the study published today in Nature Geoscience. "Forests can become lakes in the course of a month, landslides occur with no warning, and invisible methane seep holes can swallow snowmobiles whole."
Abrupt permafrost thaw can occur in a variety of ways, but it always represents a dramatic abrupt ecological shift, Turetsky added.
"Systems that you could walk on with regular hiking boots and that were dry enough to support tree growth when frozen can thaw, and now all of a sudden these ecosystems turn into a soupy mess," Turetsky said.
Permafrost contains rocks, soil, sand, and in some cases, pockets of pure ground ice. It stores on average twice as much carbon as is in the atmosphere because it stores the remains of life that once flourished in the Arctic, including dead plants, animal and microbes. This matter, which never fully decomposed, has been locked away in Earth's refrigerator for thousands of years.Nature is now a player in our climate crisis. It's time we began to add these GHG feedback loops into our climate change planning. The threat isn't just man-made emissions any more.
"The impacts from abrupt thaw are not represented in any existing global model and our findings indicate that this could amplify the permafrost climate-carbon feedback by up to a factor of two, thereby exacerbating the problem of permissible emissions to stay below specific climate change targets," said David Lawrence, of the National Center for Atmospheric Research (NCAR) and a coauthor of the study.
The findings bring new urgency to including permafrost in all types of climate models, along with implementing strong climate policy and mitigation, Turetsky added.The inescapable fact is that our timelines for slashing greenhouse gases are out of whack with reality. We don't have until 2050.