Ground Temperature and Active Layer Regimes and Changes

Abstract

Permafrost is degrading worldwide due to climate, leading to serious consequences for regional hydrology, climate, and ecosystems. Over the past decades, field observations in most permafrost regions of the Northern Hemisphere showed a warming trend in ground temperatures. The warming magnitude of low-temperature permafrost was significantly higher than that of high-temperature permafrost. Measurements from the CALM network revealed that in 2016, the increasing trend in the active layer thickness at all Arctic sites was about 1.2–1.9 cm/year across circum-Arctic regions. This change is at or near the long-term maximum for the past 18–21 years. This chapter discusses and reviews permafrost observation networks/programs and datasets, ground temperature variations, active layer changes, effect of snow cover on ground thermal regimes, ground ice distribution, carbon storage in frozen ground, and InSAR application in the northern regions. It is important to emphasize that northern permafrost conditions have significantly changed and will continue to change in the future. In order to understand the past history and future of permafrost, we need to continue and expand the monitoring of the permafrost variables, particularly ground temperature and active layer thickness, via in situ and remote-sensing technologies.