Large stocks of peatland carbon and nitrogen are vulnerable to permafrost thaw

Abstract

Northern peatlands have accumulated large stocks of organic carbon (C) and nitrogen (N), but their spatial distribution and vulnerability to climate warming remain uncertain. Here, we used machine-learning techniques with extensive peat core data (n > 7,000) to create observation-based maps of northern peatland C and N stocks, and to assess their response to warming and permafrost thaw. We estimate that northern peatlands cover 3.7 ± 0.5 million km2 and store 415 ± 150 Pg C and 10 ± 7 Pg N. Nearly half of the peatland area and peat C stocks are permafrost affected. Using modeled global warming stabilization scenarios (from 1.5 to 6 °C warming), we project that the current sink of atmospheric C (0.10 ± 0.02 Pg C⋅y−1) in northern peatlands will shift to a C source as 0.8 to 1.9 million km2 of permafrost-affected peatlands thaw. The projected thaw would cause peatland greenhouse gas emissions equal to ∼1% of anthropogenic radiative forcing in this century. The main forcing is from methane emissions (0.7 to 3 Pg cumulative CH4-C) with smaller carbon dioxide forcing (1 to 2 Pg CO2-C) and minor nitrous oxide losses. We project that initial CO2-C losses reverse after ∼200 y, as warming strengthens peatland C-sinks. We project substantial, but highly uncertain, additional losses of peat into fluvial systems of 10 to 30 Pg C and 0.4 to 0.9 Pg N. The combined gaseous and fluvial peatland C loss estimated here adds 30 to 50% onto previous estimates of permafrost-thaw C losses, with southern permafrost regions being the most vulnerable.

Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2020

“…As permafrost in the Arctic thaws, large carbon and nitrogen stocks are exposed for decomposition [ 320 ]. Gaseous carbon release from Arctic soils due to permafrost thawing is substantial [ 1 ], and growing evidence suggests that Arctic soils may also be relevant sources of nitrous oxide (N 2 O) [ 317 , 320 – 324 ].…”

“…As permafrost in the Arctic thaws, large carbon and nitrogen stocks are exposed for decomposition [ 320 ]. Gaseous carbon release from Arctic soils due to permafrost thawing is substantial [ 1 ], and growing evidence suggests that Arctic soils may also be relevant sources of nitrous oxide (N 2 O) [ 317 , 320 – 324 ]. Nitrous oxide is a source gas for stratospheric nitrogen oxides and an ozone depleting substance (contributes to SDGs 13.1, 15.1); it has an almost 300 times stronger global warming potential than CO 2 on a 100-year time horizon [ 322 ].…”

Peat deposits store more carbon than trees in forested peatlands of the boreal biome

“…Terrestrial vegetation is a key component in global climate cycles through its capacity for carbon (C) sequestration 1 . In the boreal biome, forests cover ~ 8% of the land area and sequester approximately 272 ± 23 Gt of carbon 2 , while northern peatlands store an estimated 415 ± 150 Gt of carbon, covering only ~ 2% of the global land surface 3 .…”

Carbon dioxide and methane exchange of a patterned subarctic fen during two contrasting growing seasons

“…Northern mires have sequestered substantial amounts of atmospheric carbon (C) since the last glacial period. The C 30 storage of these peat soils has been estimated to be 415 ± 150 Pg of C (Hugelius et al, 2020), which adds up to about 30% of the global soil C. This C storage has accumulated through the photosynthetic fixation of carbon dioxide (CO2) by mire vegetation, which in the long term has been larger than the release of C through plant respiration and peat decomposition. In the short term, however, the C balance of a mire can switch from a sink to a source, as the annual C accumulation rate is sensitive to variations in moisture conditions and temperature (Alm et al, 1999; https://doi.org/10.5194/bg-2020-370 Preprint.…”