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The rapid warming of the Arctic-Boreal region has led to the concern that large amounts of methane may be released to the atmosphere from its carbon-rich soils, as well as subsea permafrost, amplifying climate change. In this review, we assess the various sources and sinks of methane from northern high latitudes, in particular those that may be enhanced by permafrost thaw. The largest terrestrial sources of the Arctic-Boreal region are its numerous wetlands, lakes, rivers and streams. However, fires, geological seeps and glacial margins can be locally strong emitters. In addition, dry upland soils are an important sink of atmospheric methane. We estimate that the net emission of all these landforms and point sources may be as much as 48.7 [13.3–86.9] Tg CH4 yr−1. The Arctic Ocean is also a net source of methane to the atmosphere, in particular its shallow shelves, but we assess that the marine environment emits a fraction of what is released from the terrestrial domain: 4.9 [0.4–19.4] Tg CH4 yr−1. While it appears unlikely that emissions from the ocean surface to the atmosphere are increasing, now or in the foreseeable future, evidence points towards a modest increase from terrestrial sources over the past decades, in particular wetlands and possibly lakes. The influence of permafrost thaw on future methane emissions may be strongest through associated changes in the hydrology of the landscape rather than the availability of previously frozen carbon. Although high latitude methane sources are not yet acting as a strong climate feedback, they might play an increasingly important role in the net greenhouse gas balance of the Arctic-Boreal region with continued climate change.

Climate change is an existential threat to the vast global permafrost domain. The diverse human cultures, ecological communities, and biogeochemical cycles of this tenth of the planet depend on the persistence of frozen conditions. The complexity, immensity, and remoteness of permafrost ecosystems make it difficult to grasp how quickly things are changing and what can be done about it. Here, we summarize terrestrial and marine changes in the permafrost domain with an eye toward global policy. While many questions remain, we know that continued fossil fuel burning is incompatible with the continued existence of the permafrost domain as we know it. If we fail to protect permafrost ecosystems, the consequences for human rights, biosphere integrity, and global climate will be severe. The policy implications are clear: the faster we reduce human emissions and draw down atmospheric CO2, the more of the permafrost domain we can save. Emissions reduction targets must be strengthened and accompanied by support for local peoples to protect intact ecological communities and natural carbon sinks within the permafrost domain. Some proposed geoengineering interventions such as solar shading, surface albedo modification, and vegetation manipulations are unproven and may exacerbate environmental injustice without providing lasting protection. Conversely, astounding advances in renewable energy have reopened viable pathways to halve human greenhouse gas emissions by 2030 and effectively stop them well before 2050. We call on leaders, corporations, researchers, and citizens everywhere to acknowledge the global importance of the permafrost domain and work towards climate restoration and empowerment of Indigenous and immigrant communities in these regions.