Permafrost In a Warming World

Permafrost is permanently frozen soil, and occurs mostly in high latitudes. Permafrost comprises 24% of the land in the Northern Hemisphere, and stores massive amounts of carbon. As a result of climate change, permafrost is at risk of melting, releasing the stored carbon in the form of carbon dioxide and methane, which are powerful heat-trapping gases. In addition, permafrost is structurally important, and its melting has been known to cause erosion, disappearance of lakes, landslides, and ground subsidence. It will also cause changes in plant species composition at high latitudes.
Figure 1. Locations where permafrost exists in the Arctic (northern high latitudes). Click on the graphic for a larger image. Source: Philippe Rekacewicz, 2005.

The Effect of Climate Change on Permafrost

Permafrost is soil that has been frozen year round for at least two years. Permafrost comprises 24% of Northern Hemisphere land (Figure 1), and is also found, to a lesser extent, in the Southern Hemisphere. The upper layer of permafrost, or the active layer, sometimes thaws in the summer. Recently, the active layer of permafrost has been observed to be getting larger with time, which means more permafrost is melting each summer. This is not unexpected—the high latitudes are expected to warm much more than low latitudes as the atmosphere continues to warm (Figure 2).

Climate change is expected to significantly affect above and below-ground climate. Although widespread changes to permafrost usually take centuries, the IPCC estimates that by the mid-21st century, the area of permafrost in the northern hemisphere will decline by 20-35%. Additionally, the United Nations Environmental Programme suggests the depth of thawing could increase by 30-50% by the year 2080.

Recent studies have shown that there has been a decrease in freezing during the cold season in North America's permafrost regions. Coastal areas and eastern Canada have started to see significant increases in warm season thawing of permafrost. This means there has been a decrease in freeze depths and in the amount of permafrost, and an increase in the area of the active layer. The increase in the active layer doesn't mean there's more ground being frozen, it means more permafrost is melting seasonally, losing its distinction as "permanent." Permafrost is not only affected by climate change, but eventually will affect climate change itself by releasing the greenhouse gases it stores.

Figure 2. Expected changes in Arctic temperatures by the year 2090. Blue solid line is current permafrost boundary (orange). Blue dashed line is projected permafrost boundary by 2090. Click on the graphic for a larger image. Source: Hugo Ahlenius, 2005.

Greenhouse Gas Emissions

Permafrost stores an immense amount of carbon and methane (twice as much carbon as contained in the atmosphere). In a warming environment, permafrost is expected to degrade, and these gases which have been in storage will be released. This process has already begun in some parts of the world, including western Siberia, and is expected to increase in earnest by the year 2020. Furthermore, as of 2011, no climate model incorporates the effects of methane released from melting permafrost, suggesting that even the most extreme climate scenarios in the models might not be extreme enough.

Carbon

A third of the Earth's soil carbon is found in the Arctic tundra soil, stored in frozen organic matter. If the high northern latitudes warm significantly (as they are expected to; see Figure 3), permafrost will thaw, allowing the organic matter within the permafrost to decompose. The decomposition will release carbon into the atmosphere. This already happens within the active layer each summer. As the active layer thaws, some organic matter decomposes. Under normal climate conditions (i.e. a cold arctic region), the ground remains cold enough to keep the decomposition very slow. But as air temperature increases and the ground warms, this process will speed up, and scientists think this could begin very soon. Some suggest the arctic tundra could go from being a carbon sink to a carbon source by the mid-2020s.

Researchers at the National Snow and Ice Data Center estimate that by 2200, 60% of the Northern Hemisphere's permafrost will probably be melted, which could release around 190 billion tons of carbon into the atmosphere. This amount is about half of all the carbon released in the industrial age. The affect this will have on the rate of atmospheric warming could be irreversible. At the very least, these estimates mean fossil fuel emissions will have to be reduced more than currently suggested to account for the amount of carbon expected to discharge from melting permafrost.

Peatlands are also expected to be impacted by global climate change. Peat is made up of dead organic material, and so is very rich in carbon. It consists of 90% water and 10% plant matter, and is mostly found at the high latitudes of the northern hemisphere, both at the surface and below. Some of this peat is found underneath the permafrost layer, which means the carbon it harbors could be in jeopardy should the permafrost melt. In a study of the world's peatlands, one recent study found that if the globe warms 1°C over the next few decades, this could lead to a release of 38-100 million tons of carbon per year from peat alone.

Methane

Figure 3. Methane bubbles. Image credit: Walter et al., 2006.

In moist areas, most of the emissions will be of methane, a greenhouse gas that has 20 to 25 times more warming power than carbon dioxide. As the ground warms, methane will either be released directly into the atmosphere or bacteria will break it down into carbon dioxide, which will then be released. If areas of thawed permafrost exist at depth between frozen layers, it's possible that microbial activities will continue unabated, even during the winter, to create new methane from organic material.

This is what is believed to be happening around Siberia's lakes. In 2006, researchers working at two northern Siberian lakes found that methane was bubbling up from thawing permafrost at a rate five times faster than originally thought. The study also found an expansion of "thaw lakes" in the permafrost regions. Studies conducted in Canadian and Swedish permafrost and peatland regions also show these trends.

Methane hydrates can be thought of as methane gas frozen into ice structures, like the one in Figure 5. They're formed at cold temperatures and under high pressure—conditions that are both present beneath layers of frozen permafrost. The amount of methane hydrates in permafrost could range anywhere from 7.5 to 400 billion tons of carbon-equivalent.

Methane hydrates are abundantly present in and near the Siberian Ice Complex, or Arctic Shelf, which provides a shelf-like structure to support the land and coastline on top of it. As waters along the northern coast warm, the ice complex melts, allowing for quick erosion compared to the historical rate. In these areas, the water contains 2500% of the methane found in average atmospheric conditions. And recent research shows the amount of methane currently being released from the Arctic Shelf region is around the same amount of methane being released from all the oceans in the world. This is particularly dangerous because of the Shelf's shallow depth. In other regions where methane hydrates exist, they are deep enough to oxidize to carbon dioxide before reaching the surface. In this region, the methane is released directly into the air.

The Global Monitoring Division of NOAA's Earth System Research Laboratory allows you to plot time series of various atmospheric gases, including CO2 and CH4.

Hunting for methane with Katey Walter Anthony, UAF 2010. University of Alaska Fairbanks Professor Katey Walter Anthony takes us onto a frozen lake in Fairbanks, AK to demonstrate why methane gas has "exploded" onto the climate change scene.
Figure 4. Structure of a gas hydrate (methane clathrate) block. Image credit: Wikipedia.

The Disaster Scenario

It's not hard to imagine a disaster scenario surrounding permafrost. As the atmosphere warms, permafrost melts, which releases greenhouse gas, which further warms the atmosphere, which speeds up the permafrost melting, and so on. Currently, climate models do not incorporate the effects of methane released from melting permafrost, which means even the most extreme warming scenarios we've come up with might not be extreme enough. A spike in atmospheric methane concentration could set off catastrophic global warming.

David Shindell and Gavin Schmidt (climate scientists of RealClimate) suggest that a real-world disaster scenario would be an instantaneous release of about 10 gigatons carbon-equivalent (gton C) of methane into the atmosphere. Right now, it contains approximately 3.5 gton C of methane.

They don't see any way to get more than 1 gton C as methane into the air emitted at one time, fortunately, but the world has seen a massive release of methane in the past: the Paleocene Eocene Thermal Maximum (PETM). Studies focusing on this time period estimate that several thousand gton C of methane were released into the atmosphere. But, although it's hard to accurately conclude how long it took for this to happen, current estimates are around a thousand years. In other words, it wasn't immediate. But the warming that is occurring due to anthropogenic climate change is unprecedented in its rate—the world is warming ten times faster today that in did in the PETM. For this reason, it's hard to rule out any disaster global warming scenario.

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