How does the rapid warming and destruction of permafrost in Norway and Iceland indicate a period of global warming? Is this phenomenon a warning to humans?

With the EU-funded PACE project at the end of this century, several deep boreholes

(100 m +) were drilled at European mountain sites, including mainland Norway, Svalbard and Sweden. During other projects from c. 2004 and the International Polar Period (IPY) in

2006/07, several additional boreholes were drilled at various sites in Norway and Iceland.

Temperature measurements along elevational and latitudinal gradients. At most sites, multi-temporal geophysical sonography using seismic and electrical resistivity tomography (ERT) is available. Here we study the development of permafrost and ground temperatures in mainland Norway and Iceland based on this dataset. We document that permafrost is warming at a rapid rate, including the development of talc in Norway and Iceland in response to climate change over the past 20 years. At most sites, ground surface temperatures (GST) appear to be increasing more strongly than surface air temperatures (SAT). Changing snow conditions appear to be the most important factor for higher GST rates. Modeling exercises also show that talc development can be explained by both higher air temperatures and increased snow cover.Permafrost is thermally defined as the ground (i.e. the lithosphere) at a temperature of 0°C or less for at least two consecutive years (van Oerdingen, 1998). Since the 18th century, permafrost has been recognized as an important geomorphological factor governing the development of specific landforms and generating geotechnical problems for construction (cf. French, 1996). More recently, permafrost has been recognized as a major carbon reservoir that can be mobilized and released as greenhouse gases upon thawing (Hughlios et al., 2014; Miner et al., 2022). In addition, permafrost is a key component for the stability of steep rock walls or debris flowset al., 2023). Permafrost and the Earth's thermal regime also appear to be important factors in modulating the rate of geomorphological processes (Bertling and Etzelmüller, 2011) and ultimately landscape development (Andersen et al., 2015; Egholm et al., 2015; Hills and Roering, 2007; Hills and Roering, 2009; Etzelmüller et al., 2020b). Western Scandinavia and Iceland are located in the transition zone between regions dominated by permafrost from mountain to Arctic conditions towards Svalbard and eastern Greenland. In Currently, Norway has an extensive network of boreholes where we measure subsurface temperatures along elevational and latitudinal gradients (Etzelmüller et al., 2020a; Farbrot et al., 2011; ​​Christiansen et al., 2010; Solid et al., 2003). In addition, at most sites multi-temporal geophysical surveys using e.g. electrical resistivity tomography (ERT) are available. In Iceland, four boreholes have been in place since 2004, of which three boreholes were originally drilled in permafrost. Finally, daily gridded datasets of meteorological parameters such as air temperature and precipitation (Lussana et al., 2018a; Lussana et al., 2018b) and associated modelled snow cover (Saloranta, 2016; Czekirda et al., 2019) are available back to 1957 for Norway and 1959 for Iceland. This allows for an assessment of the relationship between climate and the Earth's thermal regime along regional gradients. This study maps changes in the thermal status of permafrost in Norway and Iceland based on borehole monitoring between 2004 and 2022. This study shows how climate change has rapidly warmed and degraded mountain glaciers and discusses possible drivers of these changes