Thawing Permafrost: Why It Matters

, senior climate scientist | August 5, 2016, 11:47 am EST
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In these recent hot summer days, as my colleague Xinnan Zhu was walking outside exposed to the outdoor temperature of nearly 100°F, she felt like she was going to melt like an ice cube under the sun. As the Arctic Climate Impacts Stanback researcher, it was far more hot and humid outside our UCS office than the work we were focusing on this summer, the opportunities for the Arctic Council and the first ever White House Arctic Science Ministerial.

Xinnan Zhu

Figure 1. Xinnan Zhu is taking the master of Environmental Management Program at Duke University and is the Arctic Climate Impacts Stanback researcher this summer at the Union of Concerned Scientists.

This feeling involuntarily reminded Xinnan of what is happening in the Arctic under the effect of global warming. However, the sea ice melt is not the only environmental issues triggered by climate change. Here is what Xinnan has prepared to help convey the perils of ignoring Arctic permafrost.

The perils of ignoring Arctic permafrost

Starting from the late 2000s, thawing permafrost has become a growing Arctic issue being mentioned and investigated by the researchers and scientists as a side effect of the global warming. Yet, the majority of the public might not have even heard about permafrost.

So for this blog, we will introduce you to permafrost including its definition, global distribution, formation and the associated environmental risks. The reason why the thawing permafrost becomes an urgent issue that needs more attention will be explained at the end.

Permafrost distribution: Nearly a quarter of the exposed land area in the Northern Hemisphere

Permafrost is defined as ground (soil, rock, or organic materials) that remains at or below 0°C for at least two consecutive years. Most permafrost is located within or near the Arctic and some in the Antarctic region, however, the alpine permafrost is also found at high mountain region with lower latitude such as Qinghai-Tibetan Plateau in China.

Northern Hemisphere Permafrost

Figure 2. Permafrost distribution map in the Northern Hemisphere. Four types of permafrost: continuous permafrost, discontinuous permafrost, sporadic permafrost and isolated permafrost. Map by Philippe Rekacewicz, UNEP/GRID-Arendal; data from International Permafrost Association, 1998. Circumpolar Active-Layer Permafrost System (CAPS), version 1.0. Accessed on 2017-07-10 at http://bit.ly/29RUdYr .

Based on the lateral continuity of distribution, permafrost is generally classified as continuous permafrost, discontinuous permafrost, sporadic permafrost and isolated permafrost, typically in high latitude regions or isolated patches in mountainous regions. Another type of permafrost is found in the Arctic Ocean, called subsea permafrost. It was once part of the exposed continent in the glacial era and now is under the sea with the rising sea level after major ice sheets and glaciers melt.

Globally, permafrost covers an area of 18,782 *106 km2, about 24% of the exposed land in the northern hemisphere, with approximately 65% in Eurasia and the other 35% in North America and Greenland.

Permafrost formation and soil layers

As leaves fall down onto the ground, neither carried away by wind or flushed away by rain, they remain and are eaten by microbes and decompose, are covered with dust, sediments or other organic materials and finally “disappear” as a part of the soil. This describes dominant processes for how soil is formed. However, in the case of permafrost, the process changes whenever the temperature is below zero.

Traced back to hundreds of thousands of years ago (during the Quaternary period), the organic matter settled and mixed with other dust and sediment loads from floodplains and other processes. Plant remains (leaves or roots) and animal bones were frozen before complete decomposition occurred when the temperature decreased below zero. Under repeated glacial periods, this frozen ground was formed and buried under the ground through geologic processes.

Permafrost or frozen ground longer than 2 years

Figure 3. Permafrost soil column. Figure created by Xinnan Zhu in July, 2016.

The vertical soil temperature varies, and it depends on the air and deep geothermal gradient temperature as well as the distance to the soil surface and Earth’s core. The vertical soil column is divided into three layers called active layer, permafrost, and talik. The active layer is the top soil that is seasonally frozen, since it is affected by the seasonal air temperature. The bottom talik layer is the unfrozen ground heated by the deep geothermal gradient. Permafrost lies between the active layer and deep talik, as a continuously frozen layer. The thickness of the permafrost ranges from less than a meter in the discontinuous permafrost to 1450m in the northern Siberia. In the continuous permafrost in the northern hemisphere, the typical thickness ranges from 350m to 650m.

Thawing permafrost

We have to admit the fact of global warming not only because we ourselves are experiencing the consequences, but also it is confirmed by the data. The global mean surface temperature study by NASA showed a 0.5-1°C increase during the period of 1960-2011in most of the lower 48 states of the United States. However, the Arctic region has warmed twice or even more than the world average. The latest data of the global surface temperature in June, 2016 showed a peak of temperature increase at the 70ºN (within the Arctic Circle) about three times higher than the global mean.

NASA GISS Surface Temperature Analysis June 2016

Figure 4. Base Map is the global mean surface temperature change in June 2016 compared with 1951-1980 average with a global mean temperature anomaly of 0.78°C. The inset figure is the zonal mean temperature anomaly at each latitude with the peak high temperature anomaly of 2.2°C at 69°N. Source from: Surface Temperature Analysis (GISTEMP) in the NASA Goddard Institute for Space Studies. Dataset accessed 2016-07-19 at http://data.giss.nasa.gov/gistemp/maps/.

As the Arctic is warmed by climate change, not only the sea ice melts much faster, but also the permafrost in the Arctic region starts to thaw. More importantly, the thawing permafrost will have an intensifying effect on global warming. As the global mean temperature rises, the ice melts and permafrost thaws. Those old “frozen” plant remains (e.g. leaves and roots) will begin to decompose when the soil temperature exceeds 0ºC, and release carbon in the form of carbon dioxide (CO2) and methane (CH4). As these carbon gases are increasingly released to the atmosphere, global warming will be accelerated since these additional greenhouse gases can absorb more long-wave radiation and heat up the air. Based on this chain reaction, the thawing permafrost will pose a self-reinforcing cycle on global warming.

Global carbon storage

As mentioned before, permafrost contains a high concentration of frozen organic materials. How does the carbon storage compare with the other terrestrial carbon pools of soil and vegetation? How does it compare with the carbon stored in the atmosphere and the ocean?  Finally, how does it compare with fossil fuels that can be extracted from geologic sources located in either terrestrial or ocean areas?

Pre-industrial (1750) Carbon Pools

Figure 5.Gobal carbon stock for various carbon pools including atmosphere, fossil fuel, vegetation, soil, permafrost and ocean in the pre-industrial period (1750). Fossil fuel reserves data were from GEA (2006) http://bit.ly/2aZgLdW. Carbon stock data were from IPCC AR5. Background image for natural gas was from http://bit.ly/2azvUgc. Figure created by Xinnan Zhu in July, 2016.

From the global scale, carbon can be stored in the atmosphere, terrestrial and ocean, and cycle within these three pools over different time periods. According to the 2014 Intergovernmental Panel on Climate Change Fifth Accessment report (IPCC AR5), the stored carbon in permafrost  is around 1,700 Pg C (Petagram Carbon = 1015 g), even more than the carbon stored in the discovered fossil fuel reserves, and more than twice as the atmosphere carbon storage (589 Pg C in 1750 and 829 Pg C in 2011).

Furthermore, permafrost is ranked as the second largest terrestrial carbon pool right after global soil (1950 Pg C). As the global temperature increases and permafrost starts to thaw, there is the potential for a large amount of carbon gases to be released to the air. This leads to a surprising fact that the permafrost starts to change from a carbon sink (storage pool) to a carbon source (production pool).

Since industrial development starting from 1750, we burn fossil fuel for energy power, cut or burn the forests and shrubs for construction, agriculture or other land uses. All these human activities have changed the ecosystem carbon cycle and carbon storage in the pools. Over the past 260 years, we burned around 25% of the total discovered fossil fuel reserves carbon (around 375 Pg C), and a net loss of carbon from vegetation by around 20 Pg C through deforestation and land use change. In total, we lost 395 Pg C through both of these pools. Consequently, on average over 60% of that loss in carbon flowed into the atmosphere, and the rest, nearly 40%, was stored in the deep ocean. As the permafrost studies only gained data on a scale relevant for carbon cycle models in this century, it is typically excluded in global carbon cycle models, the permafrost carbon loss for the last two hundred years is hard to estimate.

Figure 6. Global carbon stock change in the industrial era (1750-2011) in the carbon pools of atmosphere, fossil fuel, vegetation and deep ocean. Error bars show the data range. Data are from IPCC AR5 (Chapter 6). Figure created by Xinnan Zhu in July, 2016.

Figure 6. Global carbon stock change in the industrial era (1750-2011) in the carbon pools of atmosphere, fossil fuel, vegetation and deep ocean. Error bars show the data range. Data are from IPCC AR5 (Chapter 6). Figure created by Xinnan Zhu in July, 2016.

The 2014 IPCC fifth Assessment report indicated that we hold high confidence that if unabated, global warming can activate the permafrost to thaw. The thawed permafrost may trigger the release (in the form of CO2 and CH4 to the atmosphere) of the huge carbon buried underneath for thousands of years. The urgent problem we are facing is that we know the fact of thawing permafrost but we are uncertain about the magnitude of carbon loss due to the limited understanding of release rates at various scenarios (i.e. levels of human activities that contribute to climate change). If the nightmare truly starts, we don’t even know how far it will go and how severe it will react to an accelerated global warming. International collaboration among the world’s scientists can help resolve the remaining questions regarding the pace of change if allowed to thaw or what it takes to keep it mostly frozen this century.  More about what we know about the future risks will be explored in an upcoming blog.

Correction (August 31, 2016): An earlier version of this post incorrectly listed the amount of the total discovered fossil fuel reserves carbon and the net loss of carbon from vegetation through deforestation and land use change. It is 375 Pg C and 20 PG C respectively, not 365 Pg C and 30 Pg C. 

Photo by Xinnan Zhu
International Permafrost Association, 1998. Circumpolar Active-Layer Permafrost System (CAPS), version 1.0.
Figure created by Xinnan Zhu in July, 2016.
NASA GISS data.giss.nasa.gov/gistemp/maps
Figure created by Xinnan Zhu from data in IPCC AR5

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  • VooDude

    “The thawed permafrost may trigger the release (in the form of CO2 and CH4 to the atmosphere) of the huge carbon buried underneath for thousands of years.”
    …or, it may not…

    Lau 2015: ”The atmospheric (atm) CH4 uptake at the study site increases with ground temperature between 0 °C and 18 °C. Consequently, the atm CH4 sink strength is predicted to increase by a factor of 5–30 as the Arctic warms by 5–15 °C over a century.”

    ”…the mineral creosols at Axel Heiberg Island in the Canadian high Arctic consistently consume atmospheric CH4.”

    ”…active atmospheric CH4-oxidizing bacteria (atmMOB) in permafrost-affected cryosols, … The atmospheric (atm) CH4 uptake at the study site increases with ground temperature between 0 °C and 18 °C. Consequently, the atm CH4 sink strength is predicted to increase by a factor of 5–30 as the Arctic warms by 5–15 °C over a century.”

    ”… the majority (87%) of Arctic permafrost is comprised of mineral (that is, carbon-poor) creosols (Hugelius et al., 2014).”

    ”… atm CH4 uptake has occasionally been reported in other permafrost-affected sites (a–k in Figure 1; Supplementary Table S1), including cryosols of high organic carbon and water saturation levels where CH4 emission was expected

    ”Recently-reported CH4 fluxes, of polar desert mineral creosols, at Ellesmere Island, Canada, over five consecutive summers, also indicate consumption of atm CH4 (a in Figure 1; Emmerton et al., 2014).”

    ”Measurement of in situ surface CH4 flux at various locations at the [Axel Heiberg Island] site during the initial thaw and into mid-summer from 2011 to 2013 consistently showed atm CH4 uptake …”

    ”Under expected patterns of climate change, [Axel Heiberg Island]will continue to be a microbial atm CH4 sink and the sink strength will vary distinctly in accordance with seasonal and inter-annual temperature variability.”

    Lau, M. C. Y., et al. 2015 “An active atmospheric methane sink in high Arctic mineral cryosols.” The ISME journal

    Jørgensen et al. 2015 Arctic tundra soils serve as potentially important but poorly understood sinks of atmospheric methane (CH4), a powerful greenhouse gas1, 2, 3, 4, 5. Numerical simulations project a net increase in methane consumption in soils in high northern latitudes as a consequence of warming in the past few decades … Here, we present measurements of rates of methane consumption in different vegetation types within the Zackenberg Valley in northeast Greenland over a full growing season. Field measurements show methane uptake in all non-water-saturated landforms studied, with seasonal averages of − 8.3 ± 3.7 μmol CH4 m−2 h−1 in dry tundra and − 3.1 ± 1.6 μmol CH4 m−2 h−1 in moist tundra. The fluxes were sensitive to temperature, with methane uptake increasing with increasing temperatures. … We conclude that the ice-free area of northeast Greenland acts as a net sink of atmospheric methane, and suggest that this sink will probably be enhanced under future warmer climatic conditions.

    Jørgensen, Christian Juncher, et al. 2015 “Net regional methane sink in High Arctic soils of northeast Greenland.” Nature Geoscience

  • VooDude

    “…nearly 40%, was stored in the deep ocean.”
    That figure was arrived at by a residual. Accountants at BP and other fuel companies tell us how much fossil fuel we burned. Knowledge of the volume of the atmosphere, and the “Keeling Curve” of atmospheric CO2 concentration tells us how much CO2 is in the atmosphere.
    Guesses as to the land sink can be had via satellites.
    The rest must be in the ocean, right?
    No proof. That is actually a logical fallacy, Argumentum ad ignorantiam. It’s a good guess, but it should not be stated as a fact. Good science includes an honest assessment of the inaccuracies and uncertainties.

  • VooDude

    “We have to admit the fact of global warming not only because we ourselves are experiencing the consequences, but also it is confirmed by the data.”
    What, exactly, is “the fact of global warming”? I’m assuming that you mean human-CO2-emissions-caused “Global Warming” … and not the generic “climate is always changing, even before human CO2 emissions happened”
    So, what data confirms that human CO2 emissions cause “Global Warming”?
    … evidence of warming is not proof that CO2 caused it
    …correlation is not proof of causation
    Only in the fantasy world of computer models is there even a hint that CO2 is causing global warming.
    Nothing in reality … no actual measurements … no evidence shows that human emissions cause warming.
    None.

  • Gregg Willcox

    I appreciate your aticle! Lots of interesting information, and I agree with you on most of these major points, but work on your introduction (wordy, and a largely strained connection to the information below) and your graphics (white text on white background doesn’t work, clean up how you present important facts).