Permafrost Thermometry

In addition to direct interactions with the climate system, permafrost has been successfully used as a decadal- and century-scale thermometer of climate change. Boreholes in frozen ground record the surface temperature history, based on the diffusion of surface temperature signals to depth. Such records have been examined extensively in recent decades, and they add to the body of evidence with respect to 20th century warming. Borehole temperatures in Alaska indicate a recent warming of up to 4°C. In other locations, borehole temperature records show negligible change or cooling. These records are accurate reflections of ground surface temperature history, but they can be difficult to interpret because of the effects of changing vegetation and snow cover, which can cause a decoupling of the air and ground temperature signals. Thermal diffusion smooths out temperature variability, so it is difficult to invert borehole temperature records for millennial-scale temperature trends.

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