Day 154 — Reading: Permafrost Thaw and Its Global Consequences

A Permafrost — ground that remains at or below 0°C for at least two consecutive years — underlies roughly one-fifth of the exposed land surface of the Northern Hemisphere, stretching across Siberia, Alaska, northern Canada and parts of the Tibetan Plateau. Some layers have remained frozen continuously for tens of thousands of years, preserving not only ice but also ancient organic material, sediment and, in rare cases, the remains of extinct animals. For decades permafrost attracted comparatively little scientific attention, regarded as a stable, almost inert feature of the polar landscape. That perception has changed markedly over the past two decades, as researchers have come to view permafrost not as a frozen backdrop to climate change but as an active participant in it.

B Each summer, the uppermost layer of permafrost-affected ground, known as the active layer, thaws and refreezes with the seasons. Long-term climate warming causes this active layer to deepen and, in the most affected regions, to fail to fully refreeze in winter. As buried ice melts, the ground above it can lose structural support and collapse, a process called thermokarst, producing uneven, pitted terrain, collapsing hillsides and rapidly expanding lakes. Arctic regions are warming at more than twice the global average rate, and satellite and ground-based monitoring stations across Siberia and Alaska have recorded a measurable deepening of the active layer at a majority of monitored sites since the 1990s.

C Perhaps the most consequential aspect of permafrost thaw is its effect on the global carbon cycle. Permafrost soils are estimated to hold roughly twice as much carbon as is currently present in the atmosphere, locked away in organic matter that has not decomposed because of the cold. As the ground thaws, microorganisms become active and begin breaking down this organic material, releasing carbon dioxide and, in waterlogged conditions, methane, a gas with a substantially stronger warming effect over short timescales. This creates what scientists describe as a feedback loop: warming thaws permafrost, thawing permafrost releases greenhouse gases, and those gases drive further warming, which in turn accelerates further thaw. Unlike emissions from factories or vehicles, this source is diffuse, difficult to measure precisely, and not accounted for in most national emissions targets.

D The thawing ground poses a direct and immediate problem for the roughly five million people who live in the Arctic permafrost zone. Buildings, roads, pipelines and airport runways constructed on the assumption of stable frozen ground are increasingly subject to cracking, tilting and subsidence. In some Siberian towns, apartment blocks have been abandoned after their foundations shifted; in Alaska, sections of the main highway connecting interior communities require frequent, costly resurfacing. Indigenous communities that rely on traditional travel routes across frozen ground report that routes considered safe a generation ago are now unpredictable or impassable for part of the year, disrupting hunting and fishing practices that have been followed for generations.

E A less predictable consequence involves what has been frozen within the permafrost itself. In 2016, an outbreak of anthrax in a remote part of Siberia was linked by investigators to the thawing of a reindeer carcass that had been infected decades earlier; the spores, preserved in frozen ground, became active once exposed. This incident drew scientific attention to the broader possibility that permafrost may harbour dormant bacteria, and even viruses, some many thousands of years old. While researchers caution that the risk this poses to human health remains poorly quantified, several laboratories have begun systematically sampling deep permafrost cores specifically to catalogue and assess such organisms before further thaw occurs.

F Responding to these interlinked risks has proved difficult. Ground temperatures across the vast permafrost zone are monitored through a patchy network of boreholes, satellite radar and remote weather stations, but coverage remains sparse relative to the area involved, and funding for expanding this network has consistently lagged behind stated scientific priorities. Climate models have historically struggled to represent permafrost carbon release with confidence, since the pace and extent of future thaw depend on numerous localised factors including soil type, vegetation cover and ice content. Some engineers have experimented with thermosiphons, devices that passively extract heat from the ground to keep it frozen, around vulnerable infrastructure, but such measures remain costly and are not a feasible solution at a continental scale.