Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Permafrost thaw and release of frozen soil carbon
Permafrost thaw and release of frozen soil carbon
Frozen high-latitude soils hold a very large carbon stock; warming deepens the seasonally thawed layer, letting microbes decompose old organic matter and release carbon dioxide or methane.
Boundary: where this process starts
Starts with: Cold, waterlogged soils preserve about 1,300 Gt of organic carbon because decomposition is frozen out
Boundary: where it ends
Ends after: Under high emissions about 5-15% of permafrost carbon is released as greenhouse gas by 2100, with decades-to-centuries continuing
Line thickness = size of impact (1 to 5)% on a line = chance a fork takes that branch📄 = pieces of evidence on a stepNegative effectLoops backHypothesisResource used up (arrow into the step)Resource used, not used upResource made or released (arrow out of the step)
What am I looking at? The concepts on every map
- Participant
- Someone or something that takes part in a process or influences it: a plant, a microbe, a river, a machine, a force. Participants are the rows of a map.
- Resource
- Something a step uses or uses up: water, oxygen, sunlight, a tool. Each step has an arrow down to the resources it uses.
- Step
- One thing that happens in a process. Every step has at least one participant and carries evidence.
- Decision fork
- A step where the process can go several ways. Every outcome is labeled with a percentage, and the percentages add up to 100%. It is not limited to yes or no.
- Loop
- A line that carries the process back to an earlier step. We record whether it reinforces or balances, how strong it is (weak, moderate, strong), and its gain (0 to 1): the share of the effect that returns on each pass.
- Size of impact
- Every line says how much the earlier step affects the next one (1 to 5), in which direction (+, -, 0), and why. Thicker lines mean bigger impact.
- Evidence
- The support for a claim: a source and what it shows. Every step, line, change and vote needs it. Click any step or line to read its evidence.
- Boundary
- Where a process starts and where it ends. Every process, and every subprocess, has a start and an end.
- Subprocess
- A step that is itself a whole process, with its own boundary, steps and lines. Click a step marked ↘ to open it. Subprocesses nest as deep as the evidence goes.
- Description
- A plain-language summary of what a process is and what it covers.
- Hypothesis
- A proposed new connection between two parts of the map that nobody has linked. It carries a prediction, a way to test it, and a count of papers on each topic and on both. It is an unverified idea until someone tests it.
Every step, with its evidence
The same information as the map, as a list you can search and share. Click a participant or resource to see everywhere it appears.
Cold, waterlogged soils preserve about 1,300 Gt of organic carbon because decomposition is frozen out
Evidence (1) · added by Cinder
- Hugelius et al. (2014) Biogeosciences 11:6573-6593: Permafrost region covers about 15% of land area but holds about half of global belowground organic carbon. (confidence 0.8)
Warming deepens the seasonally thawed active layer and thaws previously frozen organic matter (permafrost temperatures rose about 0.3 C in 2007-2016)
Evidence (1) · added by Cinder
- Biskaborn et al. (2019) Nature Communications 10:264, Permafrost is warming at a global scale: Mean permafrost temperature increased by 0.29 +/- 0.12 C from 2007 to 2016. (confidence 0.8)
Microbes decompose the thawed carbon; well-drained thaw releases mostly Carbon dioxide, saturated thaw ponds release Methane
Evidence (1) · added by Cinder
- Schuur et al. (2015) Nature 520:171-179, Climate change and the permafrost carbon feedback: Aerobic thaw releases CO2; anaerobic thaw releases CH4, a small share of carbon but a large share of warming effect. (confidence 0.7)
Under high emissions about 5-15% of permafrost carbon is released as greenhouse gas by 2100, with decades-to-centuries continuing
Evidence (1) · added by Cinder
- Schuur et al. (2015) Nature 520:171-179: Expert assessment: 5-15% of permafrost carbon released by 2100 under RCP8.5, mostly as CO2. (confidence 0.65)
Thaw settling, ponding and abrupt thermokarst collapse expose still more carbon in wet, ice-rich ground
Evidence (1) · added by Cinder
- Turetsky et al. (2020) Nature 579:32-34, Carbon release through abrupt permafrost thaw; Nature Geoscience 13:138-143: Abrupt thaw affects a small land area but could roughly double the warming impact of gradual thaw carbon release. (confidence 0.6)