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

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.