The connection between a melting Arctic and frigid temperatures on the East Coast.
Clearing snow in Norfolk, Massachusetts as a major winter storm hit. Image: EPA/MATT CAMPBELL
How cold is it? Cold enough to freeze an iguana in Palm Beach. Officials have warned residents of South Florida to look out for cold-stunned lizards falling from trees.
Meanwhile, 6,000 kilometers to the north, the Arctic has less sea ice than at any time in the 37 years that satellites have been measuring ice coverage. And while most of eastern North America is expected to be even colder by Friday, with temperatures set to plunge, Juneau, Alaska, will be a relatively balmy 6℃ (42℉).
Brooklyn. Video: Jason Koebler / GIF: Kate Lunau
What about climate change? The fact that it is cold today in Palm Springs and warm in Juneau is weather. Climate is long-term trends—years—of weather. And one of those trends is increased extreme weather, including winters too warm to ski and winters too cold to go outside.
Every winter, an extremely cold pool of air forms over the Arctic and is normally trapped in the polar vortex, a gigantic circular weather pattern around the North Pole. But the vortex is weakening, allowing the Arctic air pool to escape south when conditions are right. Researchers now believe it is the combination of a warmer Arctic and the loss of sea ice, along with a strong west-coast ridge of high pressure, that allows the polar vortex jailbreak.
Climate change is heating up the Arctic far faster than anywhere else in the world. The ice covering the Arctic Ocean has shrunk rapidly—50 percent of the summer ice extent disappeared in just the last 20 years. Without its ice cover, the Arctic Ocean is warming, especially under 24 hours of sunlight in summer. Warmer water means there is less ice even in winter, when there is 24 hours of darkness.
While it was record-breakingly cold on New Year’s Eve in parts of eastern North America, the Arctic Ocean broke a different record, with a whopping 1.35 million square kilometers less sea ice—an area the size of Texas, California, and Minnesota combined—than the 1981 to 2010 median.
Researchers have now linked the loss of sea ice in the Arctic region, along with an increase in snow cover in northern Asia, to a weaker polar vortex. This allows the Arctic air pool to escape south into North America or Europe and Asia, they found. But this doesn’t happen every winter: Last winter was the seventh warmest on record in the US. Turns out it takes “two to tango,” Jennifer Francis, a climate scientist at Rutgers University, told me via email.
When the Pacific Ocean is warm off the west coast of North America, as it is now, it strengthens a high-pressure ridge of air on the west coast. That’s led to record-breaking heat from California to Alaska over the past few weeks. The east side (or downstream side) of that high-pressure ridge is also a lot stronger, almost acting like a vacuum, sucking the Arctic air pool south away from a weakened polar vortex.
This ‘scenario is believed to have exacerbated the persistent warmth and drought in the western United States, along with cold spells in the east during the winters of 2013-2014 and 2014-2015 that were popularized as the ridiculously resilient ridge and polar vortex, Francis wrote in a new study.
When California had record-breaking warm temperatures last fall, Jonathan Martin, a professor of meteorology at the University of Wisconsin-Madison, suspected the conditions would be right for an extended cold snap in the east in early winter. “It’s colder than normal but not unusual. We’ve gotten used to milder winters,” Martin told me.
Martin has been tracking the size of the Arctic air pool during winter and discovered that it has started to shrink. Four of the five smallest cold pools on record have occurred since 2004, he found, which parallels the loss of Arctic sea ice and the increasing amounts of carbon dioxide (CO2) in the atmosphere from burning fossil fuels. “My guess is that this year’s pool will be smaller than last year,” he said.
That means there is less cold air to go around. So while it might be bitterly cold in the eastern US right now, the northern hemisphere as whole is 0.9℃ warmer than normal, while the Arctic is 3.2℃ hotter.
The cold temperatures might not be exceptional, but the winds kicked up by what’s been dubbed Winter Storm Grayson will make it dangerous because of the wind chill, warns Martin. Not to mention the dangers of temporarily stunned, cold-chilled iguanas falling from trees.
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