We see far greater risk of massive irreversible sea level rise (SLR) at 2°C, on a scale of 12–20 meters or more in the long term. The climate record of the Earth over the pat few million years is quite clear:
Sea Level Rise from Ice Sheets
We see far greater risk of massive irreversible sea level rise (SLR) at 2°C, on a scale of 12–20 meters or more in the long term. The climate record of the Earth over the pat few million years is quite clear:
Sea Level Rise from Ice Sheets
Permafrost Polygons. Image: Wikimedia Commons
Carbon Emissions from Permafrost
Limiting warming to 1.5° rather than 2°C saves 2 million square kilometers of permafrost. Permafrost carbon release (as both methane and CO2) is greater at 2°, especially in “overshoot” scenarios because once thawed, former permafrost irreversibly continues to release carbon for centuries:
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If we can hold temperatures to 1.5°C, cumulative permafrost emissions by 2100 will be about equivalent to those currently from Canada (150–200 Gt CO2-eq).
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In contrast, by 2°C scientists expect cumulative permafrost emissions as large as those of the EU (220–300 Gt CO2-eq).
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If temperature exceeds 4°C by the end of the century however, permafrost emissions by 2100 will be as large as those today from major emitters like the United States or China (400–500 Gt CO2-eq), the same scale as the remaining 1.5° carbon budget.
These permafrost carbon estimates include emissions from the newly-recognized abrupt thaw processes from “thermokarst” lakes and hillsides, which expose deeper frozen carbon previously considered immune from thawing for many more centuries.
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The “anthropogenic” carbon budget to reach carbon neutrality and remain within 1.5° of warming must begin to take these “country of Permafrost” emissions into account. Only lower emissions pathways that preserve as much permafrost as possible can minimize this potentially large contribution to future global warming, and the need for future generations to maintain negative emissions efforts to compensate for those from thawed former permafrost.
Thawing permafrost in Herschel Island, Canada, 2013. Image: Boris Radosavljevic
Scientific Editors
Sarah Chadburn, University of Exeter
Gustaf Hugelius, Bolin Centre for Climate Research, Stockholm
University Susan Natali, Woods Hole Research Center
Scientific Reviewers
Julia Boike, Alfred Wegener Institute
Örjan Gustafsson, Stockholm University
Dave Lawrence, National Center for Atmospheric Research
Vladimir Romanovsky, University of Alaska-Fairbanks
Christina Schädel, Northern Arizona University
Ted Schuur, IPCC LA SROCC, Northern Arizona University
Martin Sommerkorn, IPCC CLA SROCC Merritt Turetsky, INSTAAR / University of Guelph
What is Permafrost?
Permafrost is ground that remains frozen for at least two consecutive years, and covers nearly 25% of the Northern Hemisphere land area. It stretches across vast regions of the Arctic, especially Siberia, sometimes to a depth of over a thousand meters, and also occurs in mountain regions globally. Permafrost is a frozen mixture of soil, rocks, ice and organic material holding about twice as much carbon as currently exists in earth’s atmosphere. Cold temperatures have protected this organic matter from thawing, decomposing and releasing its stored carbon to the atmosphere for many thousands of years.
Permafrost thaw, Svalbard. Image: Jeff Vanuga / Getty
A permafrost slump, the size of a football stadium, on
the shore of an unnamed lake in the Canadian Arctic.
Image: Ed Struzik for Yale Environment 360.
Permafrost Thaw and Emissions
Models project that the area covered by near-surface permafrost (in the first few meters of soils) will decline across large regions as temperatures rise. Today, at about 1°C; the area of near-surface permafrost already has declined by about 25%. Scientists anticipate that 40% of permafrost area will be lost by 2100 even if we hold temperatures close to 1.5°C globally. Over 70% of near-surface permafrost will disappear by 2100 should temperatures exceed 4°C, however.
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As temperatures have risen however, permafrost not only has declined in area, but thawed to deeper depth and greater volume; beginning to release its stored carbon. Most of this released carbon comes as CO2. However, if permafrost thaws under wet conditions, such as under wetlands or lakes, some of that carbon enters the atmosphere as methane. While not lasting as long in the atmosphere as CO2, methane warms far more potently during its lifetime: about 30 times more than carbon dioxide over a 100-year period, and nearly 100 times more over 20 years, leading to faster and more intense warming globally.
Much more permafrost thaws and releases its stored carbon at 3°C as compared to 1.5°C. (Left) Loss of permafrost between now and 1.5ºC, and (right) loss of permafrost between now and 3ºC. Data: Community Land Model, CMIP6 Data Archive
Abrupt Thaw Events
Permafrost thaw occurs gradually over large areas, but is also vulnerable to abrupt thaw events that can result in large-scale erosion, ground collapse along hillsides and cliffs, and rapid building of new lakes or wetlands (called “thermokarst” processes). The collapsed ground rapidly exposes deeper carbon pools previously thought immune to warming over the near-term. The number of these rapid thaw events has increased as the Arctic warms, and might increase permafrost carbon emissions by as much as 50% as the planet warms to 1.5°C or more. Increasing wildfires in the Arctic due to warmer and drier conditions also cause deeper and more rapid thawing post-fire.
A 35-meter-high riverbank exposure of permafrost containing large ice wedges along the Itkillik River in northern Alaska.
Image: Mikhail Kanevskiy / UAF, Institute of Northern Engineering
Near-coast permafrost.
Image: Alaska Science Center / United States Geological Survey
Irreversible Loss
Both gradual, and abrupt thermokarst thaw processes and their emissions are irreversible on human timescales, because new permafrost carbon will take many thousands of years to form. While new vegetation growing on thawed former permafrost soils might take up some portion of these emissions, that amount is dwarfed by the sheer scale of permafrost emissions expected at warmer temperatures. In addition, some “permafrost” is actually located beneath the near-coast waters of the Arctic Ocean, on lands flooded at the end of the last Ice Age when sea-levels rose. Its current and future contribution to carbon emissions remains uncertain, but could be significant.
Different Pathways
Permafrost emissions today and in the future are on the same scale as large industrial countries, but can be minimized if the planet remains at lower temperatures. If we limit warming to 1.5°C, emissions through 2100 will be about as large as those of Canada (around 150–200 Gt CO2-eq). Should we instead reach 2°C, permafrost emissions will about equal those of the entire European Union, about 220–300 Gt CO2-eq by 2100. Even higher temperatures, exceeding 4° by 2100 if it maintains current emissions levels, will however result in up to 400–500 Gt CO2-eq additional carbon release, adding the equivalent of another United States or China to the global carbon budget, the same scale as that for the current carbon budget to remain within 1.5°C.
Bars show total carbon budgets
to stay below 1.5° and 2°. Light pink portion shows projected emissions from permafrost at these temperature levels.
Sarah Chadburn / University of Exeter
Even if warming is stabilised at 1.5, 2 or 4 °C, permafrost will continue adding to global emissions for centuries. This means that permafrost not only reduces our carbon budgets, but also burdens both us and future generations with greater negative emissions requirements to keep to a given level of warming.
Adapted from Gasser, et al. (2018).
Long-term Emissions
Calculations of the remaining planetary carbon budget must take these indirect human-caused emissions from permafrost thaw into account to accurately determine when and how emissions reach “carbon neutrality”; and not just through 2100.
Once thawed, former permafrost will continue to emit carbon for many hundreds of years, committing future generations to continually offset permafrost carbon emissions through negative emissions for some time, even after temperatures stabilize.
To remain valid, future studies must begin to count permafrost emissions as another “NDC-P” or the Naturally Determined Contribution of Permafrost.
Benefits of 1.5°C
The only means available to minimize these growing risks is to keep as much permafrost as possible in its current frozen state, holding global temperature increases to 1.5°C to also minimize negative emissions efforts by future generations. This will greatly decrease the amount of new carbon entering the atmosphere from permafrost thaw, and minimize the long-term burden of negative emissions efforts by future generations.
Permafrost thaw caused this Alaskan road to drop by 3 metres.
Image: Dr. John Cloud, NOAA / Wikimedia Commons
Learn more:
IPCC Special Report: Global Warming of 1.5°C
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IPCC Special Report on the Ocean and Cryosphere in a Changing Climate
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ICCI The Cryosphere1.5° Report
References
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