The Melting of Permafrost Ice in the North and Its Relevance To Climate Change

For thousands of years, permafrost ice in the Northern Region of Earth has remained frozen and unchanged. But eventually, it has to be known that layers of permafrost ice have become unstable and melt. Scientists who study permafrost realize that this is one of the harmful effects of climate change, as there is a correlation between it and melting permafrost. 

Studies show that layers of ice on Earth have risen in temperature as far as 6C in the 20th century. Scientists predict that there will be a tremendous melting of permafrost by the year 2100.

When the temperature of permafrost raises above 0C, it melts, as in this case the ice changes from solid to liquid. Generally, minerals and organic components left over from the ice layers remains intact as a solid. Because of this, in regions filled with a lot of ice, the melting of layers of ice will cause a lot of changes in its surface, which in the case of permafrost is soil and vice versa. 

The melting of permafrost increases the surface level of the Earth's oceans and increases erosion. Erosion occurs when layers of ice melt because soil and sediments are easily swept without ice to tie them all together.

Arctic Tundras in North Taimyr, Russia in July 1990 (The Arctic Institute, 2020)

Melting Permafrost 

By definition, permafrost is soil that has been continuously below 0 C (32 F) for two years or more, located on land or under the sea. Most common in the Northern Hemisphere, about 15% of the Northern Hemisphere or 11% of the global surface is covered by permafrost ice sheets (Obu, J., 2021). This includes most of Alaska, Greenland, Canada, and Siberia. Permafrost can also be found on mountain tops in the Southern Hemisphere and under ice-free areas of Antarctica. The term 'permafrost area' is used to describe the actual area beneath the permafrost ice sheet.

Obu, Westermann, Bartsch, et al. (2019)

The distribution of the permafrost zones together represents the permafrost area. Image adapted from Obu, Westermann, Bartsch, et al. (2019).

Permafrost does not have to be the first shallow layer on the soil. Permafrost can be from an inch to several miles away below the earth's surface. It occurs frequently in soil ice sheets, but can also be present in non-porous bedrock. Permafrost is formed from ice that holds various types of soil, sand, and rock in combination. 

Permafrost contains large amounts of biomass and decomposed biomass that has been stored as methane and carbon dioxide, making tundra soils an effective carbon sink.

Mulhern, 2020

The structure of the permafrost ice sheet. From above = active layer, ice slices, then permafrost layer that is divided into 2, permafrost layer with low ice content above, and rich ice content below, at the bottom there are melted silt deposits (Mulhern, 2020).

As global warming heats ecosystems and causes soil liquefaction, the permafrost carbon cycle accelerates and releases many of the greenhouse gases contained in these soils into the atmosphere, creating a feedback loop that accelerates the process of climate change.

Bykova, 2020

Alaska's Noatak National Protected Forest, one very warm summer in 2004 triggered a 300 m long slide associated with melting ice sheets. (Bykova, 2020).

The Relevance of the Melting of the Northern Earth's Permafrost Ice Sheet to Global Warming and Climate Change

In Earth's northern latitudes, temperatures have increased by 0.6 degrees Celsius per decade over the past 30 years, twice as fast as the global average (IPCC, 2013). This causes normally frozen soils to thaw (Romanovsky, 2013), exposing large amounts of organic carbon for decomposition by soil microbes. 

This permafrost carbon is the remains of plants and animals that have accumulated in perennially frozen soils over thousands of years, and the permafrost region contains twice as much carbon as is present in the atmosphere today (Tarnocai, 2009). The conversion of only a fraction of this frozen carbon pool into the greenhouse gases carbon dioxide (CO2) and methane (CH4) and their release into the atmosphere could increase the rate of future climate change.

Schuur, 2015

Soil organic carbon deposits (kg/m^2) are contained in 0--3 m depth intervals from northern circumpolar permafrost areas (Schuur, 2015).

With global temperatures warming, more and more permafrost ice sheets will melt and thereby release billions of tons of carbon deposits and methane contained in the frozen soil into the atmosphere. The carbon and methane that settled earlier will become food for soil microbes that come back to life after being buried and frozen in the permafrost ice sheet. 

In this way, the residue from the carbon deposits will be released by microbes into the air in the form of carbon dioxide gas (CO2) and methane gas (CH4). Even though it is known that CO2 and methane gas are greenhouse gases that can exacerbate global warming if released into the atmosphere in large quantities. 

That way, the melting of the permafrost ice sheet will accelerate the pace of climate change and global warming that humans are trying to slow down. This phenomenon is known as the climate feedback loop or climate feedback cycle.

Schuur, 2015.

The main feature that regulates the release of carbon from permafrost by climate feedback mechanism from the newly synthesized observations. (Schuur, 2015)

Explanation of picture above: Carbon stored frozen in permafrost when thawed, can enter ecosystems where conditions are predominantly aerobic (oxygen present) or soils that are predominantly anaerobic (oxygen-limited). Throughout the permafrost region, there is a gradient of saturated water sourced from mostly aerobic upland ecosystems to mostly anaerobic lowlands and wetlands.

In aerobic soils, CO2 is released by microbial decomposition of soil organic carbon, whereas CO2 and CH4 are both released from anaerobic soils and sediments. Microbial decomposition of soil organic carbon can occur at the surface of the active layer, which thaws each summer and refreezes in winter, and below the surface when freshly thawed carbon sediments are available for decomposition after emerging from freshly thawed permafrost.

Organic soil carbon decomposition varies across the landscape depending in part on plant inputs and the soil environment, and also on the depth of the soil profile. Gradual and sudden thawing processes such as top-down thawing of permafrost (increasing the thickness of the active layer) d can expose more carbon to aerobic conditions. 

Otherwise, the sudden thawing process can create wetter anaerobic conditions as the soil surface recedes, drawing in local water. Carbon can also be mobilized by erosion. Plant carbon sequestration can be stored in increased plant biomass or stored at the soil surface, which can partially offset the loss of topsoil.

Knowing how much carbon will be released from the permafrost zone in this century and beyond is critical to determining the appropriate response. Yet despite the enormous amounts of carbon in permafrost soils, emissions from these soils are unlikely to offset emissions from burning fossil fuels, which will continue to be a major source of climate forcing (Schuur & Abbott, 2011). 

The release of permafrost carbon will still be an important accelerator of climate change. After all, it takes place in remote places, far from human influence, and spreads across the landscape. And once the permafrost thaws, emissions are likely to continue for decades or even centuries.

REFERENCES

Bykova, A., (2020). Permafrost Thaw in a Warming World. The Arctic Institute's Permafrost Series Fall-Winter 2020.

IPCC. (2013). The Physical Science Basis. Contribution of working group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 996.

Mulhern, O., (2020). What is Permafrost and How is it Emitting Methane?

Obu, J. (2021). How Much of the Earth's Surface is Underlain by Permafrost?. Journal of Geophysical Research: Earth Surface, 126(5), e2021JF006123.

Romanovsky, V. E., dkk., (2010). Thermal state of permafrost in Russia. Permafrost and Periglacial Processes, 21(2), 136-155.

Schuur, E. A., McGuire, A. D., Schdel, C., Grosse, G., Harden, J. W., Hayes, D. J., ... & Vonk, J. E. (2015). Climate change and the permafrost carbon feedback. Nature, 520(7546), 171-179.

Schuur, E. A., & Abbott, B. (2011). High risk of permafrost thaw. Nature, 480(7375), 32-33.

Tarnocai, dkk., (2009). Soil organic carbon pools in the northern circumpolar permafrost region. Global biogeochemical cycles, 23(2).

The Arctic Institute (2020). A Blessing and a Curse: Melting Permafrost in the Russian Arctic. Terbit 3 November 2020.