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Extreme Winter Weather In the US Linked To a Warming Arctic (theverge.com)
A new study shows how global climate change can have ripple effects at the local level. According to the research, extreme winter weather is two to four times more likely in the eastern U.S. when the Arctic is unusually warm. The Verge reports: Researchers analyzed a variety of atmospheric data in the Arctic, as well as how severe winter weather was in 12 cities across the U.S. from 1950 to 2016. Since 1990, as the Arctic has been warming up and losing ice, extreme cold snaps and heavy snow in the winter have been two to four times more frequent in the eastern U.S. and the Midwest, while in the western U.S., their frequency has decreased, according to a study published today in Nature Communications. The study, however, only shows there might be a correlation -- not a direct causal link -- between the warming Arctic and severe winters in the U.S. And it doesn't show how exactly the two are connected, so it doesn't really add much to what scientists already knew, according to several experts.
Today's study focuses on the Arctic as the main culprit for the extreme winter weather. Previous research has suggested that the warming Arctic may disrupt the polar vortex, a ring of swirling cold air circling the North Pole. Think of the polar vortex as a river, says study co-author Judah Cohen, a climatologist and director of seasonal forecasting at Atmospheric and Environmental Research. The fast flow of this river locks up the cold air over the Arctic. But as the Arctic warms -- especially in some areas like the Barents-Kara seas north of Europe and Russia -- a boulder springs up in this river, disrupting the polar vortex and allowing the freezing Arctic air to flow south, Cohen says.
Today's study focuses on the Arctic as the main culprit for the extreme winter weather. Previous research has suggested that the warming Arctic may disrupt the polar vortex, a ring of swirling cold air circling the North Pole. Think of the polar vortex as a river, says study co-author Judah Cohen, a climatologist and director of seasonal forecasting at Atmospheric and Environmental Research. The fast flow of this river locks up the cold air over the Arctic. But as the Arctic warms -- especially in some areas like the Barents-Kara seas north of Europe and Russia -- a boulder springs up in this river, disrupting the polar vortex and allowing the freezing Arctic air to flow south, Cohen says.
They defined extreme weather under the Accumulated Winter Season Severity Index which looks primarily at rapid changes in temperature and unusually heavy snowfalls. The metric is a standard one you can find more about here http://mrcc.isws.illinois.edu/research/awssi/indexAwssi.jsp. Note that the AWSSI does not include wind, general precipitation, or most unusually high temperature events.
So, our company contracts long-term weather forecasts from DTN, which is a company that produces weather outlook for industrial utilities and agriculture in the US and Europe. They use a variety of information to estimate future weather (monthly to decade scale), and in the process, comment on how current year weather matches historical weather. They look at multi-decade trends, and point out how this season is very similar to the 1950s, etc.
The comment in last quarter's winter forecast had to do with the "polar vortex" event that is leading to the "extreme" cold snaps across the US over the last 4 years or so. There are two factors at stake here, one being the "tightness" of the high-altitude wind currents around the arctic, and a secondary "rotation" effect. Imagine that there is an oval above the arctic that oscillates short and wide, mostly centered over the pole. The boundary is like a ripple that we see as wind currents. When it is circular, cold air is trapped up by the pole, and we have mild winters in the northern continents. However, over time, the polar winds oscillate north and south, which leads to daily oscillations in weather over the winter. What we see as large temperature swings are just the wind currents oscillating past.
If the oval becomes elongated, it allows the cold air to be pulled farther south, what we call the "polar vortex" with "abnormally" colder weather than average. Cold air is pulled down from the north, then hot air is pulled up from the south, and the intersection results in more winter storms than average, depending on humidity. But that dip pattern is also not stationary, it rotates on a multi-decade-long scale. In the 1990s, the polar vortex was over Russia / East Asia, and they observed the temperature swings. The North Americans (in our short-sightedness) think that if it didn't happen here, it didn't happen. But now two decades later, the elongation has rotated over us, and suddenly we're all freaking out about catastrophic weather changes.
The forecaster's point was all of this has happened before, and all of this will happen again.
No we haven't, in south Jersey there have been at least four big snow storms here that have closed schools, work, and highways. Normally we barely have to put on a sweater in the winter and barely get an inch of snow in January and that's it. Now we have a lot of deaths on the road by people who have never had to drive in such weather before.
Florida even got snow in December and twice in January.
Twinstiq, game news
RTFA:
"Using a recently developed index of severe winter weather, we show that the occurrence of severe winter weather in the United States is significantly related to anomalies in pan-Arctic geopotential heights and temperatures" https://www.nature.com/article...
It often explains what's missing from a headline and summary....
Continue to add CO2 to the atmosphere. If we observe that average global temperatures drop over a statistically significant period then the hypothesis is disproved.
Unfortunately we've been conducting this experiment for decades and the haven't seen the observations that would disprove the hypothesis.