Long permafrost temperature records for selected sites. a Location of boreholes with long time-series data. Because some regions lack long temperature records, shorter temperature records from Greenland and Chinese mountains are included for comparison. Depth of measurements is according to the Global Terrestrial Network for Permafrost ID16: 24.4 m (ID 356), 20 m (ID 55, 79, 102, 117, 501, 710, 831, 1113, and 1710), 18 m (ID 386), 16.75 m (ID 871), 15 m (ID 854), 12 m (ID 287), 10 m (ID 265, 431), and 5 m (ID 528). The light blue area represents the continuous permafrost zone (>90% coverage) and the light purple area represents the discontinuous permafrost zones (<90% coverage). b Mean annual ground temperature over time. Colors indicate the location of the boreholes in a. Graphic: Biskaborn, et al., 2019 / Nature Communications
Long permafrost temperature records for selected sites. a Location of boreholes with long time-series data. Because some regions lack long temperature records, shorter temperature records from Greenland and Chinese mountains are included for comparison. Depth of measurements is according to the Global Terrestrial Network for Permafrost ID16: 24.4 m (ID 356), 20 m (ID 55, 79, 102, 117, 501, 710, 831, 1113, and 1710), 18 m (ID 386), 16.75 m (ID 871), 15 m (ID 854), 12 m (ID 287), 10 m (ID 265, 431), and 5 m (ID 528). The light blue area represents the continuous permafrost zone (>90% coverage) and the light purple area represents the discontinuous permafrost zones (<90% coverage). b Mean annual ground temperature over time. Colors indicate the location of the boreholes in a. Graphic: Biskaborn, et al., 2019 / Nature Communications

16 January 2019 (AWI) – Global warming is leaving more and more apparent scars in the world’s permafrost regions. As the new global comparative study conducted by the international permafrost network GTN-P shows, in all regions with permafrost soils the temperature of the frozen ground at a depth of more than 10 metres rose by an average of 0.3 degrees Celsius between 2007 and 2016 – in the Arctic and Antarctic, as well as the high mountain ranges of Europe and Central Asia. The effect was most pronounced in Siberia, where the temperature of the frozen soil rose by nearly 1 degree Celsius. The pioneering study has just been released in the online journal Nature Communications.

Roughly one sixth of the land areas on our planet are considered to be permafrost regions, which means the soils there have remained permanently frozen for at least two consecutive years. In most of these regions, however, the cold penetrated the ground millennia ago; as a result, in the most extreme cases, the permafrost continues to a depth of 1.6 kilometres. Especially in the Arctic, people rely on the permafrost soil as a stable foundation for houses, roads, pipelines and airports. Yet in the wake of global warming, the integrity of these structures is increasingly jeopardised, creating enormous costs. In addition, permafrost soils contain massive quantities of preserved plant and animal matter. If this organic material thaws along with the permafrost, microorganisms will begin breaking it down – a process that could produce enough carbon dioxide and methane emissions to potentially raise the global mean temperature by an additional 0.13 to 0.27 degrees Celsius by the year 2100.

AWI permafrost scientists investigate the eroding coastline at the Siberian island Sobo-Sise, Eastern Lena delta. Photo: Guido Grosse / Alfred Wegener Institut Helmholtz Zentrum für Polar und Meeresforschung
AWI permafrost scientists investigate the eroding coastline at the Siberian island Sobo-Sise, Eastern Lena delta. Photo: Guido Grosse / Alfred Wegener Institut Helmholtz Zentrum für Polar und Meeresforschung

A new comparative study released by the GTN-P (Global Terrestrial Network for Permafrost) shows for the first time the extent to which permafrost soils around the world have already warmed. For the purposes of the study, the participating researchers monitored and analysed the soil temperature in boreholes in the Arctic, Antarctic and various high mountain ranges around the world for ten years. The data was gathered at depths greater than 10 metres, so as to rule out the influence of seasonal temperature variations.

The complete dataset encompasses 154 boreholes, 123 of which allow conclusions to be drawn for an entire decade, while the remainder can be used to refine calculations on annual deviation. The results show that, in the ten years from 2007 to 2016, the temperature of the permafrost soil rose at 71 of the 123 measuring sites; in five of the boreholes, the permafrost was already thawing. In contrast, the soil temperature sank at 12 boreholes, e.g. at individual sites in eastern Canada, southern Eurasia and on the Antarctic Peninsula; at 40 boreholes, the temperature remained virtually unchanged.

In individual cases, temperature spiked up to 1 degree Celsius

The researchers observed the most dramatic warming in the Arctic: “There, in regions with more than 90 percent permafrost content, the soil temperature rose by an average of 0.30 degrees Celsius within ten years,” reports first author Dr Boris Biskaborn, a member of the research group Polar Terrestrial Environmental Systems at the Potsdam facilities of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research. In northeast and northwest Siberia, the temperature increase at some boreholes was 0.90 degrees Celsius or even higher. For the sake of comparison: the air temperature in the respective regions rose by an average of 0.61 degrees Celsius in the same period.

Farther south, in Arctic regions with less than 90 percent permafrost, the frozen ground only warmed by 0.2 degrees Celsius on average. “In these regions there is more and more snowfall, which insulates the permafrost in two ways, following the igloo principle: in winter the snow protects the soil from extreme cold, which on average produces a warming effect. In spring it reflects the sunlight, and prevents the soil from being exposed to too much warmth, at least until the snow has completely melted away,” Biskaborn explains.

Permafrost temperature and rate of change near the depth of zero annual amplitude. a, b Mean annual ground temperatures for 2014–2016 in the Northern Hemisphere and Antarctica, n = 129 boreholes. c, d Decadal change rate of permafrost temperature from 2007 to 2016, n = 123 boreholes (Eq. 3). Changes within the average measurement accuracy of ~±0.1 °C are coded in green. Continuous permafrost zone (>90% coverage); discontinuous permafrost zones (<90% coverage). Graphic: Biskaborn, et al., 2019 / Nature Communications
Permafrost temperature and rate of change near the depth of zero annual amplitude. a, b Mean annual ground temperatures for 2014–2016 in the Northern Hemisphere and Antarctica, n = 129 boreholes. c, d Decadal change rate of permafrost temperature from 2007 to 2016, n = 123 boreholes (Eq. 3). Changes within the average measurement accuracy of ~±0.1 °C are coded in green. Continuous permafrost zone (>90% coverage); discontinuous permafrost zones (<90% coverage). Graphic: Biskaborn, et al., 2019 / Nature Communications

Significant warming can also be seen in the permafrost regions of the high mountain ranges, and in the Antarctic. The temperature of the permanently frozen soils in the Alps, in the Himalayas and in the mountain ranges of the Nordic countries rose by an average of 0.19 degrees Celsius. In the shallow boreholes in the Antarctic, the researchers measured a rise of 0.37 degrees.

“All this data tells us that the permafrost isn’t simply warming on a local and regional scale, but worldwide and at virtually the same pace as climate warming, which is producing a substantial warming of the air and increased snow thickness, especially in the Arctic. These two factors in turn produce a warming of the once permanently frozen ground,” says Prof. Guido Grosse, Head of the Permafrost Research Section at the Alfred Wegener Institute in Potsdam.

Permafrost monitoring calls for an institutional framework

These revealing insights are the reward for a decade-long international collaboration that involved experts from 26 countries. The majority of the boreholes used in the study were drilled and equipped with measuring equipment during the International Polar Year 2007/08, and offered a first “snapshot” of the permafrost temperatures. Since then, more than 50 different research groups have performed regular maintenance on the measuring stations, and recorded their readings on an annual basis. In the virtual network GTN-P, the findings were subsequently collated and standardised, ensuring their intercomparability.

According to Prof. Hanne H. Christiansen, co-author of the study and President of the International Permafrost Association (IPA), “Monitoring global permafrost temperatures and gathering the data in the freely accessible GTN-P database is tremendously important – and not just for researchers, educators and communicators, but for various other users.”

Annual permafrost temperature change. a–d Permafrost temperature departure ΔT¯y,b calculated from mean annual ground temperatures in boreholes near the depth of zero annual amplitude Z* relative to the 2008–2009 reference period. Mean values calculated as de-clustered, indexed area-weighted averages (Eq. 1). Temperature uncertainties are expressed at 95% confidence. Sample size shown is the number of borehole sites per year and region. Graphic: Biskaborn, et al., 2019 / Nature Communications
Annual permafrost temperature change. a–d Permafrost temperature departure ΔT¯y,b calculated from mean annual ground temperatures in boreholes near the depth of zero annual amplitude Z* relative to the 2008–2009 reference period. Mean values calculated as de-clustered, indexed area-weighted averages (Eq. 1). Temperature uncertainties are expressed at 95% confidence. Sample size shown is the number of borehole sites per year and region. Graphic: Biskaborn, et al., 2019 / Nature Communications

“The permafrost temperature is one of the most universally accepted climate variables. It offers a direct insight into how the frozen ground is reacting to climate change,” the researcher explains. This information is above all essential in those permafrost regions where the soil has already grown warmer or begun thawing, producing major damage when the ground buckles, destabilising roads and buildings. Accordingly, the researchers plan to continue monitoring the boreholes.

Unlike weather observations, there is still no single international institution that, following in the footsteps of the World Meteorological Organization (WMO), successfully bundles national interests. Such an institution would be an essential asset in terms of coordinating these important scientific measurements, and to ensure the monitoring sites continue to be used in the future.

To date, the permafrost boreholes and the temperature sensors installed in them have been kept up and running by individual research groups in the context of various small-scale projects. The Global Terrestrial Network for Permafrost (GTN-P) offers a web-based data management system (gtnpdatabase.org), which was jointly developed by the Alfred Wegener Institute and the Iceland-based Arctic Portal, and was made possible by the financial support of the European Union.

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The pace at which the world’s permafrost soils are warming

Annual air temperature and snow depth changes. a–d Air temperature anomaly ΔT^y,b relative to the 1981–2010 reference period calculated from mean annual air temperatures at 2-m height above the ground level interpolated from the ERA Interim reanalysis data set. Mean values calculated as de-clustered, indexed area-weighted averages (Eq. 4). Dark colored dashed lines indicate 4-year end-point running means. Snow depth changes ΔS^y,b in a and b, indicated in gray, calculated as the difference relative to the 1999–2010 reference period from the CMC reanalysis data set (eq. 5). e, f Onset of snow SO, snow insulation maximum SIM (dashed line), and the end of snow melt SE. Uncertainties are expressed as shading at 95% confidence. Sample size n indicates the number of boreholes. Graphic: Biskaborn, et al., 2019 / Nature Communications

ABSTRACT: Permafrost warming has the potential to amplify global climate change, because when frozen sediments thaw it unlocks soil organic carbon. Yet to date, no globally consistent assessment of permafrost temperature change has been compiled. Here we use a global data set of permafrost temperature time series from the Global Terrestrial Network for Permafrost to evaluate temperature change across permafrost regions for the period since the International Polar Year (2007–2009). During the reference decade between 2007 and 2016, ground temperature near the depth of zero annual amplitude in the continuous permafrost zone increased by 0.39 ± 0.15 °C. Over the same period, discontinuous permafrost warmed by 0.20 ± 0.10 °C. Permafrost in mountains warmed by 0.19 ± 0.05 °C and in Antarctica by 0.37 ± 0.10 °C. Globally, permafrost temperature increased by 0.29 ± 0.12 °C. The observed trend follows the Arctic amplification of air temperature increase in the Northern Hemisphere. In the discontinuous zone, however, ground warming occurred due to increased snow thickness while air temperature remained statistically unchanged.

Permafrost is warming at a global scale