Arctic Ice Loss a Factor in Weather Extremes – New Study
October 30, 2013
New research linking loss of arctic ice to increased rain in the UK, drying around the Mediterranean, and more Greenland Melt.
“In the UK, summer 2012 was the wettest for over 100 years, with frequent occurrences of flooding that caused damage to property and some fatalities; and profound impacts on local farming and tourism,” said Screen. “At the same time Arctic sea ice was very low. The six summers from 2007 to 2012 witnessed the six lowest amounts of sea ice on record, with summer 2012 the all-time low.”
In order to check whether there’s a link between melting Arctic sea ice and wet UK summers, Screen changed the amount of sea ice in a climate model – the UK Met Office Unified Model – whilst keeping constant other factors that affect European weather. Decreasing the amount of sea ice cover in the model caused a shift towards wetter summers over the UK and north-west Europe.
“The pattern of rainfall anomalies in the model looked very similar to the pattern of rainfall anomalies in recent years,” said Screen. “This led to the conclusion that the loss of Arctic sea ice is one factor that has likely contributed to increased rainfall in recent summers.”
Melting Arctic sea ice causes the jet stream (currents of strong winds roughly 10 km up in the atmosphere) to shift further south than normal, Screen found, increasing the frequency of cloudy, cool and wet summers over north-west Europe.
Dr Screen used a state-of-the-art atmospheric model to compare the mid-latitude circulation during conditions of extensive sea ice (representative of the late 1970s) to that with much reduced sea ice (representative of present day). Except for the sea-ice extent and ocean temperatures where ice was lost, all surface conditions were fixed at climatological values in the model, thereby isolating the influence of sea-ice loss. Observation-constrained reanalysis fields were composited for the wettest and driest summers in northern Europe and used to verify the model simulations.
The atmospheric responses to reduced sea ice in both real and modeled worlds show not only precipitation patterns in Europe similar to those observed during the past six abnormally wet summers, but they also reveal features in the large-scale circulation that appear coincident with unusual weather patterns experienced elsewhere around the northern hemisphere in recent years. For example, the meridional wind anomalies near the jet-stream level suggest that reduced sea ice favors enhanced ridging over the western N. Atlantic, which is consistent with increased high-pressure blocking observed during June and expanded melting of the Greenland ice surface
Below, recent video of Jennifer Francis and Jeff Masters explaining the ice/jetstream connection.