Examining the Influence of Greenland Ice Sheet Melting and Atlantic Meridional Shutdown on the Climate of Scandinavia and the British Isles

Earth’s climate has been rapidly changing over the last hundred years, and its global average temperature is rising. However, climate change is far more complicated than a simple increase in temperature. For example, Earth’s general ocean-atmosphere circulation includes significant heat transport from the tropics poleward, partly through the Atlantic Meridional Overturning Circulation (AMOC). AMOC has slowed down significantly within the last 150 years, compared to the last millennium. Further, the increasing average temperature of Earth is causing the Greenland Ice Sheet (GrIS) to melt. This injection of cold, fresh water into the overturning region of AMOC will likely slow AMOC further. The heat transport of AMOC is vital to Earth maintaining its current climate. In particular, AMOC is responsible for areas in Northern Europe (including Scandinavia and the British Isles) being warmer and more habitable than is typical for their latitudes. Without the heat transport of AMOC, these regions could become cooler. This research examines if climate change, through GrIS melting and AMOC slowdown, could contribute to cooler, instead of warmer, conditions in Scandinavia and the British Isles.

The Weather Research and Forecasting model (WRF) was used to emulate a slowdown of AMOC via a widespread 5 K sea surface temperature decrease near the southern coast of Greenland. An experiment was run for a 1979-2009 time period over a domain covering Greenland, the British Isles and Scandinavia, forced by the NCEP Climate Forecast System (CFS). Two model runs were performed: a control run, and an anomaly run including the -5 K sea surface temperature anomaly.

The difference between the resulting climatologies included a surface temperature anomaly in Scandinavia and the British Isles of roughly -0.1 K for the anomaly run, with a larger anomaly present in winter months. This lower temperature anomaly was also positively correlated with the North Atlantic Oscillation (NAO). Other features of the anomaly run included a lower tropopause for the region and drier air in Scotland and Scandinavia, both more intense during winter months. Precipitation effects varied, but analysis revealed a positive relative humidity anomaly in the British Isles which led to a 1% increase in yearly total precipitation, and a 10-20% increase in yearly snowfall in the anomaly run. Modeling thus shows that a slowdown of AMOC, and lower sea surface temperatures in the North Atlantic, would lead to generally cooler conditions, and, in some areas, an increase in snowfall for Scandinavia and the British Isles.