Science Feature: New evidence links Arctic warming with severe weather in mid-latitudes, but more research and long-term observations are needed to resolve mechanisms

-Contributed by James Overland, NOAA/PMEL, USA

FigureA OverlandFigure A: North America: Warmer Arctic temperatures can reinforce wavy Jet StreamIt is too soon to know for certain whether the Arctic played a role in cold events during recent winters, but new studies add to the growing weight of evidence linking increased Arctic temperatures with changes in mid-latitude weather patterns. This is according to research published in the Journal of Climate by authors from North America, Asia and Europe, that paints a picture of linkage mechanisms that vary by region and season.

“We are in the pre-consensus stage of a theory that links continued warming of the Arctic with some severe weather events,” noted Edward Hanna, an author of “The melting Arctic and Mid-latitude weather patterns: Are they connected?”

Arctic temperatures are increasing two to three times faster than those at the mid-latitudes. Some scientists have theorized that warming Arctic temperatures contribute to weaker upper level westerly winds and a wavier jet stream. This wavier path may have caused cold weather conditions to stall over the eastern seaboard and Midwest United States during recent winters, according to these theories.

It’s still a dotted line from Arctic warming to the destabilized or wavier jet stream and persistent weather regimes. Observations span too short a time period, less than 15 years, to conclude that Arctic warming plays a major role.  A combination of forces — including tropical energy, varying sea surface temperatures, mountain ranges, and chaotic atmospheric motions – likely interacted to create the unusually tenacious pattern. Case studies for North America suggest that a warming Arctic can also contribute to the cold pattern being more persistent (Figure A).

FigureB OverlandFigure B: Asia: Arctic-Midlatitude weather linkagesIn other regions and seasons, such as in eastern Asia (Figure B), robust mechanisms are emerging. The loss of sea ice and warmer temperatures north of central Asia increase the intensity of the Siberian high pressure system. This weather feature, in turn, fuels cold storms that can reach Japan, South Korea, and parts of China.

A way to advance research from a pre-consensus stage is to further investigate of the fundamental atmospheric circulation features, such as the meandering jet stream and the connection between the warmer Arctic and the negative phase of the Arctic Oscillation, an index of the dominant pattern of sea level air pressure in the Arctic.

“We are where other major theories such as plate tectonics and El Niño were before they were widely accepted,” said James Overland, the lead author. “We need a Grand Science Challenge to advance weather forecasting abilities and climate change prediction.”
New studies of the changing Arctic and subarctic low frequency dynamics, together with additional Arctic observations, can contribute to improved skill in extended-range forecasts as planned by the WMO Polar Prediction Program (PPP).

Citation: The Melting Arctic and Mid-latitude Weather Patterns: Are They Connected? By James Overland, Jennifer A. Francis, Richard Hall, Edward Hanna, Seong-Joong Kim, and Timo Vihma published in the Journal of Climate, doi: 10.1175/JCLI-D-14-00822.1