Communities around the Arctic are already seeing the effects of melting permafrost. Some of the biggest effects of this thaw will probably emerge in the coming centuries.
Nearly one-quarter of the land in the Northern Hemisphere is underlain by permafrost. As this frozen soil melts, it releases large amounts of carbon dioxide and methane, and also alters surface hydrology. In this focus, we present a collection of research and comment pieces that look at the current effects of melting permafrost and assess how this vast carbon store could influence climate in the future.
Climate change is causing widespread permafrost thaw in the Arctic. Measurements at 33 Arctic lakes show that old carbon from thawing permafrost is being emitted as methane, though emission rates have not changed during the past 60 years.
The sources contributing to the deglacial rise in atmospheric CO2 concentrations are unclear. Climate model simulations suggest thawing permafrost soils were the initial source, highlighting the vulnerability of modern permafrost carbon stores.
Warming thaws permafrost, releasing carbon that can cause more warming. Radiocarbon, soil carbon, and remote sensing data suggest that 0.2–2.5 Pg of carbon has been emitted from permafrost as CO2 and CH4 around Arctic lakes since the 1950s.
Atmospheric CO2 concentrations rose during the last deglaciation, but the carbon sources are unclear. Climate and carbon cycle simulations suggest that permafrost melting was the main source of carbon between 17,500 and 15,000 years ago.
From the archives
Methane emissions from natural gas reservoirs have long been largely overlooked. The discovery of abundant geological gas seeps in areas of cryosphere degradation highlights the relevance of these emissions to the greenhouse gas budget.
Large quantities of methane lie trapped beneath the floor of the Arctic Ocean. Measurements in the southern Laptev Sea around the Lena River delta suggest that bubbles and storms facilitate the flux of some of this submarine methane to the atmosphere.
Lakes are sources of the greenhouse gas methane. A synthesis of measurements of methane emissions reveals that lakes and ponds above 50 °N emit 16.5 Tg methane annually, and emissions may increase by 20 to 50% with longer ice-free seasons.
The impact of thawing permafrost on the nitrogen cycle is uncertain. Laboratory experiments using permafrost cores from northeast Greenland reveal that rewetting of thawed permafrost increases nitrous oxide production over 20-fold.
Acidification of East Siberian Arctic Shelf waters through addition of freshwater and terrestrial carbon
Uptake of atmospheric CO2 contributes to ocean acidification. Measurements of seawater chemistry reveal that the extreme acidity of the East Siberian Arctic Shelf is driven by terrestrial organic matter and freshwater inputs.
Permafrost soils contain almost twice as much carbon as the current atmospheric carbon pool. Climate model simulations suggest that the feedback generated by future permafrost carbon release could lead to a further warming of 0.13–1.69 °C by 2300.
High Arctic soils can act as sources or sinks of methane. Scaled-up field measurements suggest that northeast Greenland’s ice-free soils currently act as a net sink for methane, and may take up more methane with rising temperatures.
Vast quantities of carbon are stored in shallow Arctic reservoirs, such as subsea and terrestrial permafrost. Observations in the Laptev Sea suggest that bubbles deliver significant quantities of the methane stored in subsea permafrost to the overlying water column.
The polygonal patterns in permafrost regions are caused by the formation of ice wedges. Observations of polygon evolution reveal that rapid ice-wedge melting has occurred across the Arctic since 1950, altering tundra hydrology.