A new study has revealed a shocking new insight. An Abrupt thawing of permafrost will double previous estimates of potential carbon emissions.
Let’s take a look.
Study: Carbon release through abrupt permafrost thaw
Published in Nature Geoscience on 3rd Feb 2020 it studies the impact of abrupt permafrost melt.
The Permafrost contains vast amounts of carbon. Roughly about 60% of the world’s soil carbon is held in just 15% of the global soil area. This is estimated to be about 1.5 trillion metric tons of carbon. Rapid warming at high latitudes is causing accelerated decomposition of this permafrost car- bon, releasing greenhouse gases into the atmosphere. Rather obviously this will have a huge impact upon the climate system.
Gradual vs Abrupt thaw
Gradual thaw slowly affects soil by centimetres over decades. Abrupt thaw can affect many metres of permafrost soil in periods of days to several years.
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. It also releases 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.
Why does this matter?
As the climate warms, then rather obviously the permafrost cannot remain frozen.
Across the arctic about 80% of the permafrost will thaw gradually. As for the other 20%, this study paper estimates that it will be abrupt. This brings extreme consequences on the landscape and the atmosphere, especially where there is ice-rich permafrost. This fast process is called “thermokarst” because a thermal change causes subsidence. This leads to a karst landscape, known for its erosion and sinkholes.
Turetsky said this is the first paper to pull together the wide body of literature on past and current abrupt thaw across different types of landscapes.
The authors then used this information along with a numerical model to project future abrupt thaw carbon losses. They found that thermokarst always involves flooding, inundation, or landslides. Intense rainfall events and the open, black landscapes that result from wildfires can speed up this dramatic process.
The researchers compared abrupt permafrost thaw carbon release to that of gradual permafrost thaw, trying to quantify a “known unknown.” There are general estimates of gradual thaw contributing to carbon emissions, but they had no idea how much of that would be caused by thermokarst.
Global Climate Models & Thermokarst
None of the current climate models incorporate thermokarst, and only a handful consider permafrost thaw at all. While large-scale models over the past decade have tried to better account for feedback loops in the Arctic, the Intergovernmental Panel on Climate Change (IPCC)’s most recent report only includes estimates of gradual permafrost thaw as an unresolved Earth system feedback.
“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.
“We can definitely stave off the worst consequences of climate change if we act in the next decade,” said Turetsky. “We have clear evidence that policy is going to help the north and thus it’s going to help dictate our future climate.”
Assumptions
The main goal of the study was to assess how abrupt thaw emissions compare with those estimated for widespread gradual thaw, under similar modelling conditions and warming scenarios.
They achieved this by assuming that abrupt thaw rates will increase similarly to gradual thaw rates with climate change as predicted by large-scale models. They do however recognise that this assumption is a substantial simplification. Nobody knows whether this assumption would over- or underestimate abrupt thaw expansion.
This is an important knowledge gap because the sensitivity of gradual thaw to climate change may not be the same as abrupt thaw, which can be triggered by a single weather extreme.
In addition, once initiated, abrupt thaw features can evolve with self-reinforcing feedbacks such as continued thaw subsidence with increasing water depth and volume in the case of lakes and with changes in vegetation and albedo in thaw wetlands . These feedbacks cause abrupt thaw to become
less dependent on external climate after initiation, as indicated by the presence of actively expanding thaw lakes even in High Arctic cold permafrost regions today.
Models of abrupt thaw succession
The study also illustrates three pathways of ecosystem succession and changes with simulated abrupt thaw formation and stabilization.
The first is in hillslope/upland landscapes where abrupt thaw leads to slumps, active layer detachments and gullies …
The second is lowland mineral landscapes with the formation of thaw lakes
The third is lowland organic landscapes with the formation of thaw lakes or wetlands.
Within all three, the assessment period between 1900 and 2000 (dashed lines) was based on historical transition rates between successional states. Between 2000 and 2300 (solid lines), the assessment simulates increasing permafrost thaw rates under the worst-case RCP8.5 climate projection, as projected by large-scale models.
Permafrost – Further Reading
- Study in Nature Geoscience (3 Feb 2020) – Carbon release through abrupt permafrost thaw
- University of Colorado Bolder – Arctic permafrost thaw plays greater role in climate change than previously estimated