Experts Estimate of Carbon Emissions from Subsea Permafrost

Environmental Research Letters, December 22

Emissions from subsea permafrost – existing in near-coastal waters, mostly inundated at the end of the last Ice Age – long have comprised a question mark for global carbon budgets.  This expert assessment, with 32 co-authors estimated the total amount of subsea permafrost as containing 560 Gt carbon in organic matter; and 45 Gt methane gas (CH₄).  Today’s annual emissions into the water column, at 1.1°C of warming above pre-industrial, were estimated at 18 megatons CO2, and 38 megatons of methane, based however on scarce observations given the patchwork nature of measurements by different research expeditions and other entities, such as oil companies that rarely release their data.  The group of experts then projected that under a high emissions scenario, subsea permafrost could release 43 gigatons of CO2-equivalent by 2100 to the water column; and 190 gigatons by 2300. Following a low emissions pathway however, consistent with 1.5°C would reduce these values by about a third.

These figures all had large amounts of uncertainty; and the amount of methane and CO2 that would make it through the water column and be released into the atmosphere adds an additional layer of uncertainty.  Nevertheless, this was the first such consensus estimate; and authors emphasized the need for more open sharing of data, and greater amounts of data collection to improve our understanding of current and future carbon emissions from this potentially large source; in order to reduce the risk of policy makers underestimating carbon feedbacks, leading to overshoot of carbon budgets and temperature targets.

https://iopscience.iop.org/article/10.1088/1748-9326/abcc29

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