Evidence of accelerated englacial warming in the Monte Rosa area, Switzerland/Italy

Abstract

Abstract. A range of englacial temperature measurements was acquired in the Monte Rosa area at the border of Switzerland and Italy in the years 1982, 1991, 1994, 1995, 1999, 2000, 2003, 2007 and 2008. While the englacial temperatures revealed no evidence of warming at the firn saddle of Colle Gnifetti at 4452 m a.s.l. between 1982 and 1991, the 1991 to 2000 period showed an increase of 0.05 °C per year at a depth of 20 m. From 2000 to 2008 a further increase of 1.3 °C or (0.16 °C per year) was observed. The measured temperatures give clear evidence of accelerated glacier warming since 1991. The observed increase since 2000 is far beyond a modelled firn temperature increase based on the IPCC climate scenario from 2001. Air temperature records from the Jungfraujoch high-altitude station (MeteoSwiss-Station) from 1980 to 2008 show a mean annual increase of 0.05 °C per year, indicating that the amount of infiltrating and refreezing of meltwater at Colle Gnifetti has increased since 2000. The drill sites on Colle Gnifetti are, however, still located in the recrystallisation-infiltration zone and only marginally affected by meltwater. A much stronger warming of 6.8 °C was found at locations beneath Colle Gnifetti from 1991 to 2008. This warming is one order of magnitude greater than the atmospheric warming and can be explained only by a strong increase in the latent heat input by infiltrating and refreezing meltwater. The observations indicate that since 1991, an important firn area beneath Colle Gnifetti has already undergone a firn facies change from the recrystallisation-infiltration to the cold infiltration zone due to an increasing supply of surface melt energy.