Why is Eastern North America so cold and the globe so hot?

'Temperature Anomaly' is how different the current temperature is from the expected temperature. Source: University of Maine.

‘Temperature Anomaly’ is how different the current temperature is from the expected temperature. Source: University of Maine.

Temperatures across the Great Lakes and Eastern United States are setting cold temperature records for the first half of February, 2015, according to the Northeast Regional Climate Center.  Compared to expected temperatures, it is the coldest region of the planet. And even in absolute terms, parts of the Northeast have been colder than Anchorage, Alaska.

However, this cold isn’t everywhere.  In fact, you could go almost anywhere else on the globe and have the opposite experience. That’s because the world as a whole is actually much warmer than the historical average, consistent with ongoing climate change and global warming.  Western North America, Europe, Asia, Australia, Africa and the Arctic are all much warmer right now than their historical mean temperatures for this time of year.

This pattern of a uniquely cold Northeast has held throughout the last two winters.  The Eastern United States has been experiencing much colder weather than average, while the rest of the world has been experiencing hotter than normal conditions.  While NOAA determined 2014 to be the hottest year on record globally, the Eastern United States stands out as a cold spot in a hot world.

So what is going on here in the East?  While ‘global warming’ is clear in the map of temperature records across the globe, overall ‘climate change’ is more subtle.  Some regions may experience more warming than others and some locations might even experience cooling for a while, while the overall globe warms.

The Eastern U.S. was one of the few regions on the planet that saw colder than average temperatures in 2014. Source: NOAA.

The Eastern U.S. was one of the few regions on the planet that saw colder than average temperatures in 2014. Source: NOAA.

Such differential effects can result if the total global temperature rise actually changes the patterns of atmospheric circulation and ocean temperatures and currents.  Is that what is happening here? Are the last couple of cold winters in Eastern North America actually a feature of the overall warming, driven by changes in atmospheric circulation?

Many in the Northeast would like to know, because that would tell us if we should expect more winters like these in the decades ahead. But the answer is not yet clear.

Some climate scientists have hypothesized that the warming Arctic and the loss of Arctic sea ice lasting through the summer is changing the behavior of the jet stream in a way that contributes to both the heat waves and drought in the western half of the North America and the Arctic break-outs of cold air afflicting the eastern half (Overland, Nature Climate Change, 2014, Vol 4, p.11-12).  This is still a very controversial issue, however, and other climate scientists think that these regional patterns are just normal annual variation, albeit against a background of overall warming.

The question of how climate change is changing the likelihood of these interconnected regional weather contrasts is an extremely active field where more is known every day, but a definite answer on whether this Eastern cold spell is directly related to climate change is not yet known for certain.



Category: What's With the Weather

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