Winter Snow and Global Warming
The global warming trend of climate change and the recent huge winter snow storms in the US and Europe are consistent, because both exist. A new line of inquiry by Overland et al. and by Petoukhov et al. suggests that global warming and the recent huge snow storms are actually causally linked.
Here's why. The jet stream, which circulates the globe mostly west-to-east azimuthally with some meanders (see video and picture below), usually provides a "barrier" that contains the cold winter Arctic weather near the north pole. However, the jet stream sometimes destabilizes, so that the barrier becomes "broken", large south-north meanders occur, and the jet stream thus no longer contains the cold Arctic weather. Now, with global warming, the Arctic has been heating up, with Arctic sea ice melting at an unprecedented rate. The causal connection proposed is that this additional Arctic heat contributes to the destabilization of the jet stream so that the barrier breaks more than it would under natural variation. The most visible result of Arctic weather leaking out to the south has been the huge snow storms in the US and Europe when the jet stream moves south in those regions. Other regions (jet stream moving north) heat up. Since it is not possible to predict the exact location of the meanders with time, it is not possible to predict which regions become temporarily cold or warm. However, with more meanders, the extremes in weather (warm and cold) increase.
HERE is a video by Dr. Jennifer Francis (Rutgers U) on the connection between the jet stream and extreme weather:
See the References below for details.
What are the lessons?
1. Global warming has unexpected regional consequences, and this may be one of them.
2. The contrarian/denier conjecture that US winter snow storms and global warming are incompatible, is wrong, independent of the proposed causal connection. See HERE to learn about contrarians.
What's the picture? From J. Overland et. al, the broken jet stream "barrier" (purple regions), which normally circumnavigates the Arctic, becomes displaced so the Arctic weather leaks into regions away from the north pole. It is proposed that this effect is enhanced due to rising Arctic temperatures (due in turn to global warming).
Here is a diagram showing what the jet stream normally looks like (Wikipedia):
Quantitative attribution - namely, how much of the effect is anthropogenic, will require more evidence. Specifically, the proposal is plausible because there is a qualitative explanation that is based on some scientific evidence, but as a caveat, quantitatively highly speculative because evidence for causation of recent winter circulation patterns by climate change is weak (the sea ice anomalies that are purported to cause the response have only prevailed for a few years, not nearly long enough for proper detection-attribution studies).
J. Overland, M. Wang, and J. Walsh, "Arctic Report Card"
There continues to be significant excess heat storage in the Arctic Ocean at the end of summer due to continued near-record sea ice loss. There is evidence that the effect of higher air temperatures in the lower Arctic atmosphere in fall is contributing to changes in the atmospheric circulation in both the Arctic and northern mid-latitudes. Winter 2009-2010 showed a new connectivity between mid-latitude extreme cold and snowy weather events and changes in the wind patterns of the Arctic; the so-called Warm Arctic-Cold Continents pattern.
"Cold and snowy winters will be the rule, rather than the exception," says Dr James Overland of the NOAA/Pacific Marine Environmental Laboratory in the United States. Dr Overland is at the International Polar Year Oslo Science Conference (IPY-OSC) to chair a session on polar climate feedbacks, amplification and teleconnections, including impacts on mid-latitudes.
Petoukhov, V. and Semenov, Vladimir (2010), Journal of Geophysical Research - Atmospheres . ISSN 0148-0227
The recent overall Northern Hemisphere warming was accompanied by several severe northern continental winters, as for example, extremely cold winter 2005/2006 in Europe and northern Asia. Here we show that anomalous decrease of wintertime sea ice concentration in the Barents-Kara (B-K) Seas could bring about extreme cold events like winter 2005/2006.
Our results imply that several recent severe winters do not conflict the global warming picture...
Stanford, CA—The Earth’s jet streams, the high-altitude bands of fast winds that strongly influence the paths of storms and other weather systems, are shifting—possibly in response to global warming. Scientists at the Carnegie Institution determined that over a 23-year span from 1979 to 2001 the jet streams in both hemispheres have risen in altitude and shifted toward the poles. The jet stream in the northern hemisphere has also weakened. These changes fit the predictions of global warming models and have implications for the frequency and intensity of future storms, including hurricanes.
[n.b. This article shows the poleward shift trend of the mainly east-west moving jet stream is due to global warming. This is in addition to the recent volatility destabilizating the jet stream, also possibly due to global warming, allowing Arctic weather to leak into the US and Europe].
Last winter’s big snowfall and cold temperatures in the eastern United States and Europe were likely caused by the loss of Arctic sea ice, researchers concluded at the International Polar Year Oslo Science Conference in Norway last week.
Jet streams sometimes form huge loops over North America, with segments flowing from north to south or south to north – what scientists call meridional flow. These loops can even break into separate pieces. But meridional flow is not the usual pattern, and such winds tend to have lower velocity than their west-to-east counterparts.
Lately, though, we’ve seen more north-to-south jet streams. These winds have dragged cold air out of the Arctic and delivered it to populated regions of North America and Europe.