Arctic temperature anomaly oct nov 2016 NSIDC

Rapid Arctic warming connected to cooler winters in Northern mid-latitudes

A recent study presents evidence that there are two key Arctic regions where regional warming can induce cold winters over northern continents.  Since 1998 trends in winter surface air temperature in the Northern Hemisphere have become conspicuously different from those between 1979 and 1997.  First, there have been stronger warming trends over regions of the Arctic ocean.  Secondly, strong cooling trends have been evident in the mid-latitudes over northern continents.  Many parts of the northern continents have experienced frequent cold extremes.  The study found that warming over the Barents–Kara Sea Arctic region is likely to lead to East Asian cooling, whereas northern North America cooling is closely related to warming over the East Siberian–Chukchi Sea Arctic region.

Introduction

Arctic amplification, surface warming over the Arctic occurring twice as rapidly as over the entire Northern Hemisphere, has accelerated in recent decades. Between 1998 and 2013 the pattern of winter surface air temperature (SAT) trends in the Northern Hemisphere became conspicuously different from that between 1979–1997.   Stronger warming trends have been observed over the Barents–Kara and East Siberian–Chukchi sea regions.  Secondly, strong cooling trends have been evident over parts of the mid latitudes of northern continents resulting in many parts of the northern continents experiencing frequent cold extremes.

Surface air temperature trends in 1979-1997 and 1998-2013
Trend in observed surface air temperature during December–February for 1979/1980–1997/1998 (a) and 1997/1998–2013/2014 (b)

This trend can be seen in the illustration. In the 1998-2013 period the Arctic was cooling slightly whereas in the 1979–1997 period it was warming rapidly and there was evidence of rapid cooling in parts of the mid-latitude Northern Hemisphere. Recent studies have suggested that recent cold winters in northern continents are related to Arctic warming. However, it is not clear if the trend to colder winters is due to Arctic amplification or internal variability because the underlying mechanisms are not fully understood.

Comparing surface temperature trends in the Arctic and mid-latitudes

A recent study by Jong-Seong Kug et al. has investigated the observed connections between regional Arctic warming and cold winters in the northern parts of the Asian and North American continents.  The surface temperature over the Barents–Kara Sea region (30°–70° E, 70°–80° N) and over the East Siberian–Chukchi Sea region (160° E–160° W, 65°–80° N) were averaged as ART1 and ART2, respectively.

Correlating the average surface temperature  in the Barents–Kara Sea Arctic region (ART1) with weather patterns in the mid-latitudes revealed negative correlations over most of Eurasia, but particularly  strong negative correlations over East Asia. This analysis identified a trend that when the Arctic gets warmer over the Barents–Kara Sea region, East Asia experiences cold winters.

The average surface temperature  in the East Siberian–Chukchi Sea Arctic region (ART2) was found to be negatively correlated with surface air temperature in the north of North America. The negative correlation is strongest over most of Canada and the central and eastern parts of the United States.  Further research showed that these relationships are fairly robust even for long-term historical data.

Weather patterns associated with Arctic warming

Northern hemisphere atmospheric pressure trends
Linear regression of sea-level pressure (Pa) with respect to monthly ART1 and ART2 indices during December–February for the period of 1979/1980–2013/2014.

Teleconnections are changes in the atmosphere in one place affecting weather thousands of kilometers away.  Teleconnection patterns are caused by changes in the way air moves around the atmosphere and may be changed as Earth’s climate warms.  In the study Jong-Seong Kug et al. have identified possible teleconnections between regional Arctic warming and Northern Hemisphere continental cooling.

Warm conditions over the Barents–Kara Sea Arctic region are found to be associated with negative sea-level pressure (SLP) anomalies over the central Arctic and strong positive SLP anomalies over western Russia.  The result is cold advection to East Asia and the frequent occurrence of cold events in that region.

A teleconnection between warming in the East Siberian–Chukchi Sea Arctic region and cooler Alaskan and northern Canadian weather has also been identified.  In this case there is an anomalous weather pattern that leads to northerly winds bringing cold Arctic air into northern North America.

The analysis reveals that Barents–Kara Sea warming tends to precede the maximum East Asian surface temperature  response by about 15 days.   The East Siberian–Chukchi Sea warming is about 5 days ahead of the North American surface temperature response. These results imply that the atmospheric circulation anomalies associated with the continental cooling over both regions are related to regional Arctic warming.   This suggests that regional patterns of Arctic warming/cooling may be crucial for understanding mid-latitude Northern Hemisphere winter climate variability.

Conclusion

The above results clearly indicate that regional warming over the Arctic Ocean can affect the mid-latitude Northern Hemisphere climate.   Each regional warming over the Arctic Ocean is accompanied by the local development of an anomalous anticyclone and the downstream development of a mid-latitude trough. The resulting flow of cold air provides favourable conditions for severe winters in East Asia and  North America. The authors suggest that these results may help improve seasonal prediction of winter weather and extreme events in these regions.

Sources:

Two distinct influences of Arctic warming on cold winters over North America and East Asia, Jong-Seong Kug, Jee-Hoon Jeong, Yeon-Soo Jang, Baek-Min Kim, Chris K. Folland, Seung-Ki Min & Seok-Woo Son, Nature Geoscience 8, 759–762 (2015) doi:10.1038/ngeo2517

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