Rutgers researcher identifies links between Arctic warming, mid-latitude weather patterns
By Bob Berwyn
SUMMIT COUNTY — With Arctic sea ice shrinking fast — losing 40 percent of its mass between 1980 and 2007 — widespread effects on climate and weather are inevitable, according to Jennifer Francis, with Rutgers University Institute of Marine and Coastal Sciences.
“How can it not affect the weather? It’s such a huge loss in the Earth’s system,” Francis said, speaking Jan. 13 and the Glenn Gerberg Weather and Climate Summit in Breckenridge, Colorado.
Discussing the link between rapid climate changes in the Arctic and weather patterns in mid-latitudes, Francis said her most recent research points to a direct link between changes over the Arctic and mid-latitude weather patterns driven by the jet stream.
The Arctic is warming twice as fast as other parts of the Earth and essentially, that heat is changing north-south temperature gradients and reducing the speed of circumpolar winds. That leads to a greater amplification of the high pressure ridges and low pressure troughs in mid-latitudes.
As those kinks in the atmospheric circulation grow more pronounced, it slows the progression of weather systems moving from west to east around the northern hemisphere, allowing weather systems to get stuck over certain regions.
Speaking to an audience of TV meteorologists, Francis called it the “revenge of the atmosphere,” then explained some of the recent changes in the Arctic.
“When the ice was thick in the good old days … the variations we saw were caused by wind, moving the ice around a bit. The winds would change, the ice didn’t respond so much … now that it’s thinner, it moves around more,” she said.
Some of the biggest shifts came during a lengthy positive phase of the Arctic Oscillation during the 1990s, when more Arctic ice was transported directly into the Atlantic Ocean, leaving the high Arctic filled with younger and thinner ice, she said.
The end result is that, instead of thick, long-lasting ice reflecting incoming solar energy back into space, the heat is absorbed by the darker colored water.
“The open ocean absorbs heat. The change is sea-surface temperatures is dramatic … a lot more energy is being put into the Arctic ocean,” she said. “What happens to all that hear? It all goes back into the atmosphere. How can it not affect large-scale circulation?
“I expect to see two main effects,” she said, explaining that north-to-south temperature gradient drive the jet stream, and in the past several decades, there’s been a 20 percent drop in the zonal west-to-east wind speeds.
As that zonal flow slows down, it leads to those bigger kinks in the jet stream. That amplification is associated with persistent weather patterns that lead to “extremes” like drought, flooding and heat waves.
“Look at 20 coldest days in Tampa — you can see the patterns — A big ridge in the West, a big trough in East … It’s the same if you look at the wettest days in Chicago,” she said, explaining that a persistent trough of low pressure over the high plains brings moist air into the upper Midwest.
Those slow-moving, persistent waves of weather energy may have played a role in the big snows that hammered parts of the West last winter, as well as some of the extreme winter weather that hit Europe in the fall and early winter.
“Revenge of the atmosphere”