Driven by climate change, thawing permafrost is radically altering the Arctic landscape

Across the Arctic, strange things are happening to the landscape.

Massive lakes, several square miles in size, disappeared within days. Subsidence of hillsides. The ice-rich ground is collapsing, leaving the landscape undulating where it was once flat and, in places, creating vast fields of large sunken polygons.

READ MORE: How permafrost thaw is changing the Arctic

This is proof that permafrost, the long-frozen ground beneath the surface, is melting. This is bad news for the communities built above – and for the global climate.

As an ecologist, I study these dynamic landscape interactions and have documented the various ways in which permafrost-induced landscape change has accelerated over time. The hidden changes going on there are a warning for the future.

An illustration shows some of the ways permafrost affects the Arctic landscape. Victor O. Leshyk, de Schuur et al. 2022. Permafrost and Climate Change: Carbon Cycle Feedbacks of Arctic Warming. Annual Review of Environment and Resources Volume 47 (in press)

What is permafrost?

Permafrost is permanently frozen ground that covers about a quarter of the land in the Northern Hemisphere, particularly in Canada, Russia and Alaska. Much of it is rich in organic matter from plants and animals long dead and frozen in time.

These frozen soils maintain the structural integrity of many northern landscapes, providing stability to vegetated and unvegetated surfaces, similar to load-bearing support beams in buildings.

As temperatures rise and precipitation patterns change, permafrost and other forms of ground ice become vulnerable to thawing and collapse. As these frozen grounds warm, the ground destabilizes, unraveling the intertwined fabric that has delicately shaped these dynamic ecosystems over millennia. Forest fires, which have increased in the Arctic, have increased the risk.

A landscape of lakes showing one losing its water.

Ravines created by thawing ground drain a lake on the Arctic Coastal Plain of northern Alaska. Christian Andresen and Mark J. Lara, CC BY-ND

Below the surface, something else is active – and it’s amplifying global warming. When the ground thaws, microbes begin to feast on organic matter in ground that has been frozen for millennia.

These microbes release carbon dioxide and methane, powerful greenhouse gases. As these gases escape into the atmosphere, they warm the climate further, creating a feedback loop: warmer temperatures melt more soil, releasing more organic matter for microbes to feast on and produce more greenhouse gases.

The proof: endangered lakes

Evidence of human-caused climate change is accumulating throughout the permafrost.

The disappearance of large lakes, covering several square miles, is one of the most striking examples of recent patterns of northern landscape transitions.

The lakes drain laterally as wider and deeper drainage channels develop, or vertically through taliks, where the unfrozen ground beneath the lake gradually deepens until the permafrost is penetrated and the the water is flowing.

There is now overwhelming evidence that surface waters in permafrost regions are declining. Satellite observations and analyzes indicate that lake drainage could be linked to permafrost degradation. My colleagues and I have found that it increases with warmer and longer summer seasons.

This idea came after some of the highest rates of catastrophic lake drainage — drainage that occurs over a few days due to permafrost degradation — have been observed in the past five years in northwestern India. Alaska.

The disappearance of lakes in the permafrost expanse is likely to affect the livelihoods of indigenous communities, as water quality and water availability are important for waterfowl, fish and other wildlife. change.

Sunken hills and polygon fields

The thaw and collapse of buried glacial ice is also causing hillsides to sink at an increasing rate in the Russian and North American Arctic, sending soil, plants and debris sliding downwards.

A new study in northern Siberia has found that disturbed land areas have increased by more than 300% in the past two decades. Similar studies in northern and northwestern Canada found that subsidence there was also accelerating with hotter, wetter summers.

Multiple sags along one valley, with signs of more sags about to form

Hillside subsidence shows how easily the thermokarst landscape is eroding in Aulavik National Park in Canada. Sarah Beattie/Parks Canada

A person stands in front of a wedge of ice visible on an eroded hill.  The corner is more than twice the height of the person.

A late Pleistocene wedge of ice at Noatak National Preserve in Alaska. David Swanson/National Park Service

In flat terrain, wedges of ice can develop, creating unusual geometric patterns and shifts across the land.

Over decades, if not centuries, melting snow seeps into cracks in the ground, forming wedges of ice. These corners cause depressions in the ground above them, creating the edges of the polygons. Polygonal features form naturally as a result of the freezing and thawing process in a manner similar to that seen at the bottom of drying mudflats. When the ice wedges melt, the ground above collapses.

Even in the extremely cold environments of the High Arctic, the impacts of just a few exceptionally hot summers can dramatically alter the surface of the landscape, transforming previously flat terrain into rolling terrain as the surface begins to sink into depressions with melting ice in the ground below. Global rates of ice wedge melting have increased in response to global warming.

Thawing pingo and polygons – a mound and depressions formed by wedges of ice – in the Northwest Territories, Canada. Emma Pike/Wikimedia

In many parts of the Arctic, this thaw has also been accelerated by forest fires. In a recent study, colleagues and I found that wildfires in arctic permafrost regions increased the rate of thaw and vertical collapse of frozen terrain up to eight decades after the fire. Since global warming and disturbance from wildfires are expected to increase in the future, they could accelerate the rate of change in northern landscapes.

The impact of recent climatic and environmental changes has also been felt at lower latitudes in the lowland boreal forest. There, ice-rich permafrost plateaus — raised islands of permafrost raised above adjacent wetlands — rapidly degraded in Alaska, Canada and Scandinavia. They can look like cargo ships filled with sedges, shrubs and trees that burrow into wetlands.

Why is it important?

Freezing temperatures and short growing seasons have long limited the decomposition of dead plants and organic matter in northern ecosystems. As a result, nearly 50% of the world’s soil organic carbon is stored in these frozen soils.

The abrupt transitions we see today – lakes becoming drained basins, shrub tundra becoming ponds, boreal lowland forests becoming wetlands – will not only accelerate the decomposition of buried permafrost carbon, but also the decay of aboveground vegetation as it collapses in waterlogged environments.

Permafrost in the Northern Hemisphere.

Russia has much of the world’s permafrost. When Russia invaded Ukraine in early 2022, some Western institutions suspended funding for scientific studies there after years of international cooperation. Joshua Stevens/NASA

Climate models suggest that the impacts of such transitions could be disastrous. For example, a recent modeling study published in Nature Communications suggested that permafrost degradation and associated landscape collapse could lead to a 12-fold increase in carbon losses under a high-warming scenario by the end of the century.

This is particularly important because permafrost is estimated to contain twice as much carbon as the current atmosphere. Permafrost depths vary widely, exceeding 3,000 feet in parts of Siberia and 2,000 feet in northern Alaska, and decrease rapidly as you move south. Fairbanks, Alaska averages about 300 feet (90 meters). Studies have suggested that much of the shallow permafrost, 10 feet (3 meters) deep or less, would likely thaw if the world remained on its current warming trajectory.

To add insult to injury, in waterlogged, oxygen-deprived environments, microbes produce methane, a potent greenhouse gas 30 times more effective at warming the planet than carbon dioxide, although it does not remain in the atmosphere for as long.

Maps showing temperature differences with increasing red in 2050

The red areas are talik, or unfrozen ground above permafrost, expected in the 2050s in five parks in northern Alaska. Permafrost thickness varies with climatic conditions and landscape history. For example, the active layer that thaws in the summer may be less than a foot thick near Prudhoe Bay, Alaska, or a few feet thick near Fairbanks, while the average permafrost thickness beneath these sites has been estimated at about 2,100 to 300 feet, respectively (about 660 to 90 meters), but varies widely. National Park Service

How big of a problem the thawing permafrost is likely to become for the climate is an open question. We know it is now releasing greenhouse gases. But the causes and consequences of permafrost thaw and associated landscape transitions are active research frontiers.

One thing is certain: the thawing of previously frozen landscapes will continue to change the face of high latitude ecosystems for years to come. For people living in these areas, land subsidence and soil destabilization will mean living with risks and costs, including warping roads and collapsing buildings.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Teresa H. Sadler