Currently showing: Climate/natural disasters > Climate change


16 Feb 14 12:58

Oh, Global Warming, Where Art Thou? How the recent cold outbreaks in the US are consistent with, not in contradiction of, the expected impacts of climate change.

During the months of January and February, the eastern North America experienced numerous extreme winter weather events. In early January, many locations in the Midwestern United States and Canada were colder than both the North and South Poles; the extreme cold is evident in the plot of January through February temperature anomalies (deviations from average) in the plot below (source: NOAA/NCEP) . In late January and mid-February, winterstorms severely impacted areas more accustomed to heat waves, hurricanes and tornadoes; the cities of Atlanta, Raleigh-Durham and Birmingham, along with the Outer Banks of North Carolina, ground to a halt.

The recent spate of extreme cold has led many to ask, "But what about global warming? Aren't our winters supposed to be getting warmer?" Our climate, and thus weather, is primarily driven by the difference in temperature between the equator, where radiation from the sun is near constant, and the poles, where solar radiation varies strongly over the course of the year. This difference in temperature results in high altitude winds which blow from west to east; these winds, the jet stream, separate the cold polar air from the more temperate tropical and mid-latitude air. In general, the greater the temperature contrast between the equator and pole, the stronger and more zonal (west to east) the jet stream. When the difference in temperature between the equator and the pole decreases, the jet stream slackens and takes on more of a wavy pattern, with larger north to south meanders. These north to south meanders in the jet stream allow for cold Arctic air to penetrate further south, down into the United States.

One of the primary consequences of climate change is that the Arctic is warming much quicker than the equator; this is well established by the International Panel on Climate Change (IPCC). This Arctic amplification is caused by melting ice, which reveals ocean. This now exposed ocean absorbs solar radiation, instead of reflecting it as ice would, leading to additional warming and continuing ice melt. A significantly warmer Arctic, coupled with little to no appreciable temperature changes at the equator, would lead to a decrease in the temperature difference between the equator and the pole, which would in turn, lead to a weaker jet steam with more north to south meanders. Therefore, under climate change, one could expect an increase in the frequency of Arctic air outbreaks during the winter in the continental United States.


Category: Climate/natural disasters: Climate change, Floods/storms

Location: North America


8 Comments

Rashunda Tramble - 17 Feb 2014, 1:22 p.m.

Megan...thank you so much for the easily understandable explanation!!!

Alicia Montoya - 19 Feb 2014, 6 a.m.

Thanks, Megan.

For those who want to go even deeper and missed it, here's a link to a Reddit AMA (ask me anything) with Kerry Emanuel, a Professor of Atmospheric Science at MIT. He researches hurricanes and other types of severe weather, climate change, and how climate change might affect severe weather: http://www.fastcoexist.com/3026495/let-an-mit-hurricane-expert-explain-what-all-this-extreme-weather-means-for-the-planet

Andreas Schraft - 19 Feb 2014, 7:35 p.m.

Thank you Megan, you are making it easy to understand climate and weather. I guess the US could also get a very warm winter instead of a cold one. Depending on where the meanders of the jet stream are they could also block arctic air from reaching the us, resulting in mild weather. If this is the case, seasons could be much more volatile in future than what we are used to - not a pleasant outlook.

Tony Eitzen - 20 Feb 2014, 3:46 p.m.

Megan, the Artic ice this year is 60% thicker than last year, so how is the Artic warming? Antartica now has record ice levels, does this not have the opposite effect?

Megan Linkin - 20 Feb 2014, 3:56 p.m.

We're already seeing that this winter too, Andreas. While this post focuses specifically on the eastern part of the US, it's worth noting that there is record heat in the western US, extending from California, which was rain-free until very recently, all the way north to Alaska.

Megan Linkin - 20 Feb 2014, 4:14 p.m.

Hi Tony, the temperature difference between the equator and the South Pole (Antarctic) controls the jet stream in the Southern Hemisphere, and does not impact the Northern Hemisphere jet stream, which is the focus of this post. In the Arctic, there's been an on-going decline in both sea ice thickness and sea ice extent when compared to climatology (long term state of sea ice); both 2007 and 2012 set records for summer sea ice minimums, and the ice has shrunk so much that there's no time during the winter months for the ice to recover. Please visit the NSIDC link to see the sea ice trend and place 2014 in context (http://nsidc.org/arcticseaicenews/). Even with the ice being thicker than last year, sea ice extent is still well below normal. Also, please visit the NASA link to see the Arctic warming trend; there's a well-established and documented trend in Arctic surface temperature in the last several decades (http://svs.gsfc.nasa.gov/vis/a000000/a004000/a004030/).

Alicia Montoya - 21 Feb 2014, 9:22 p.m.

I hate to rub it in but meanwhile, in Switzerland, we've been basking in the sun at +15 degrees Celsius throughout February! Never thought I'd live to see that.

Zack Schmiesing - 21 Feb 2014, 10:42 p.m.

Megan-

I also find the Pettit "Climate" graphs of use and easily understandable when discussing sea ice volume, extent, and temperatures.

https://sites.google.com/site/pettitclimategraphs/pettit-climate-graphs


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