Looking for Above Normal Temperatures? They are in the Arctic.

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Despite the cold air gripping much of the U.S., Europe and Asia, there is a very large area in the Northern Hemisphere where temperatures are well above normal: the Arctic.  The National Snow and Ice Data Center (NSIDC) reported yesterday (5 January 2010) that "average air temperatures over the Arctic Ocean were much higher than normal" during December 2009.  The extraordinary atmospheric conditions may be tied to climate change and  to the rapid decline in Arctic sea ice, as well as other factors that cause climate to vary.

In our 24 December 2009 post (Don't be Fooled by Weather's Ups and Downs: The Climate is Warming -- Rapidly ) we explained that the odds of below normal temperatures are lower than they used to be -- but such conditions can still occur.  More importantly, we emphasized that it is necessary to look at the big picture -- what is happening globally and over a longer period of time. 

December is a case in point.  While most of us experienced cold conditions and heard in the news only about similar conditions elsewhere in the Northern Hemisphere, vast and sparsely populated regions of the Arctic were well above normal.  In Extreme negative phase of the Arctic Oscillation yields a warm Arctic (5 January 2010), the NSIDC included the figure below that dramatically contrasts above normal conditions in the Arctic with below normal temperatures in populated areas to the south.

Average Air Temperature Anomaly

Caption (from NSIDC):  Map of air temperature anomalies for December 2009, at the 925 millibar level (roughly 1,000 meters [3,000 feet] above the surface) for the region north of 30 degrees N, shows warmer than usual temperatures over the Arctic Ocean and cooler than normal temperatures over central Eurasia, the United States and southwestern Canada. Areas in orange and red correspond to strong positive (warm) anomalies. Areas in blue and purple correspond to negative (cool) anomalies.
—Credit: National Snow and Ice Data Center courtesy NOAA/ESRL Physical Sciences Division

Beyond giving us a more complete picture of temperatures in the Northern Hemisphere, there are other reasons why Arctic conditions matter.  They not only affect the region's wildlife, ecosystems and communities, they have consequences that spill beyond the Arctic into the rest of the northern hemisphere -- and the entire planet.  We explore many of these connections in Arctic Climate Feedbacks: Global Implications (PDF, 10.3MB).

Atmospheric pressure conditions in the Arctic have a lot to do with the temperature anomalies we are seeing.  The atmospheric pressure in the Arctic and its relationship to mid-latitude pressure can fluctuate in a pattern known as the Arctic Oscillation (AO) and its status is quantified as an index value.  When pressures are higher than normal in the Arctic and lower than normal in mid-latitudes, the AO is in its negative phase and the index is negative. The NSIDC reports that December's AO index value was -3.41, "the most negative value since at least 1950."

There is mounting evidence that atmospheric pressure patterns are changing in mid-latitudes and in the Arctic, that atmospheric circulation -- the large scale movement of air -- is changing, and that these changes are related to the rapid buildup of greenhouse gases in the atmosphere and to the associated decline in Arctic sea ice.  While some are using the recent frigid conditions in the U.S. and other regions to raise doubts about climate change science, a wider perspective instead reinforces the science and the need to seriously address climate change by reducing emissions and preparing for the impacts that are increasingly evident. 

For a recent discussion of the connection between Arctic climate change and weather changes in the northern hemisphere, see The Climate is Changing: The Arctic Dipole Emerges (Dr. Jeff Masters' WunderBlog, 11 December 2009).  According to Masters:

"The dramatic loss of Arctic sea ice in recent years has created a fundamental new change in the atmospheric circulation in the Northern Hemisphere that has sped up sea ice loss and is affecting fall and winter weather across most of the Northern Hemisphere, according to several recent studies. " [emphasis added]

Stu Ostro at the Weather Channel also is raising the alarm about the anomalous atmospheric patterns that are emerging and how those changes are reflected in unusual weather, including extreme events such as flooding rains.  As Ostro says in his posting, Off the Chain without a 'Cane (3 October 2009), climate change is altering the thickness (or depth) of different parts of the atmosphere, thereby "setting the table" for the unusual and sometimes extreme weather we are seeing.  Ostro says:

"What we've been observing over and over again in recent years is exceptionally strong ridges of high pressure, sometimes accompanied by strong, persistent "cutoff lows" (upper-level lows cut off from the main jet stream) to the south of the ridges. The upshot: many weather events/patterns in recent years which have been topsy-turvy and/or produced precipitation extremes and temperature anomalies."

Ostro concludes that "[w]hile it's important to consider what may happen in 50 or 100 or 200 years, and debate what should be done about that via H.R. 2454 or other measures, we need to get a grip on what's happening *now*." (Ostro's emphasis).

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