Thursday 31 October 2013

The Jet Stream

Study: Arctic Sea Ice Loss Shifts Jet Stream, Driving Deluges In NW Europe, Drought In Mediterranean
Yet another study finds Arctic sea ice loss can shift the jet stream and alter the climate

Joe Romm

Arctic sea ice volume in 1000s of cubic kilometers (via Robinson). A new study links recent ice loss to changes in European precipitation.

30 October, 2013

Scientists predicted a decade ago that Arctic ice loss would shift storm tracks and bring on worse western droughts of the kind we are now seeing. Recent studies find that Arctic sea ice loss may well usher changes in the jet stream that lead to more U.S. extreme weather events (see here and here).

Several studies also suggest that in Arctic sea ice loss is driving more extreme weather in other parts of the world (see review here).

Now a new study in Environmental Research Letters, “Influence of Arctic sea ice on European summer precipitation” finds a “a causal link between observed sea ice anomalies, large-scale atmospheric circulation and increased summer rainfall over northern Europe.” The University of Exeter news release explains:

A new study offers an explanation for the extraordinary run of wet summers experienced by Britain and northwest Europe between 2007 and 2012. The study found that loss of Arctic sea ice shifts the jet stream further south than normal resulting in increased rain during the summer in northwest Europe.

Dr James Screen “used a computer model to investigate how the dramatic retreat of Arctic sea ice influences the European summer climate” and “found that the pattern of rainfall predicted by the model closely resembles the rainfall pattern of recent summers.”

Here is Dr. Screen explaining his findings:

Jet streams are currents of strong winds high in the atmosphere – around the height at which aeroplanes fly. These winds steer weather systems and their rain. Normally in summer the jet stream lies between Scotland and Iceland and weather systems pass north of Britain. When the jet stream shifts south in summer, it brings unseasonable wet weather to Britain and northwest Europe causing havoc for tourism and farming.

The model suggests that while summer rainfall increases in northwest Europe, Mediterranean regions will receive less rain.

That final point is significant. It’s increasingly clear the climate models that had been predicting the countries surrounding the Mediterranean would start to dry out were correct (see “NOAA: Human-Caused Climate Change Already a Major Factor in More Frequent Mediterranean Droughts”).

We appear to have started a phase change in our weather.

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