Methane under the Arctic could trigger a climate feedback loop
Deep beneath the permafrost that blankets a group of islands in the Arctic Ocean lurks a growing and migrating sea of methane. The thick permafrost, or ground that remains frozen for at least two years, forms a tight seal that has so far prevented millions of cubic metres of methane from wafting out, but there’s no guarantee that the potent greenhouse gas won’t eventually escape. “At present, the leakage from below permafrost is very low, but factors such as glacial retreat and permafrost thawing may ‘lift the lid’ on this in the future,” said Thomas Birchall, a geologist at the University Center in Svalbard in Norway.
The base of permafrost is undulating, which creates pockets between the permafrost and the underlying geology where gas from biological and non-biological sources can accumulate and become trapped. Should this permafrost seal disintegrate, it could set off a chain reaction in which the methane’s strong warming effect would thaw more permafrost and release even more gas. This vicious feedback loop would further accelerate warming, melting and methane emissions. Permafrost is widespread on Svalbard, a Norwegian archipelago located deep inside the Arctic Circle and just 500 miles from the North Pole. Missions that involve drilling into the frozen soil in search of fossil fuels often hit pockets of natural gas by accident, but the extent of these reserves was unknown. Birchall and his colleagues used historical data from commercial and scientific boreholes to map the permafrost throughout Svalbard and pinpoint these stores of natural gas. The researchers found deposits rich in methane are much more common than thought on the islands. Given that the archipelago has a similar geological and glacial history to the rest of the Arctic region, the same could be true of other permafrost-covered locations near the
North Pole.
The permafrost seal on Svalbard isn’t uniform, the study found. Coastal areas had a thinner crust of frozen soil due to the warmth brought by ocean currents, whereas permafrost in the lowlands was thick and saturated with ice, meaning it has “extremely good sealing properties” and is able to “self-heal,” scientists said. In the highlands, the permafrost was flakier and more permeable due to dry conditions.
But permafrost that’s leak-proof now might not stay that way.
Svalbard is one of the fastest warming places on the planet, and its ‘active’ layer of permafrost, the upper few metres that thaws and refreezes seasonally, grows deeper as global temperatures rise. Estimating how much methane is trapped below the permafrost is tricky because it is difficult to access and there are only a few dozen boreholes on which to draw conclusions. “With permafrost thawing in the Arctic, there is a risk that the impacts of releasing methane trapped beneath permafrost will lead to positive climatic feedback effects.