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 at 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 (at right) 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 air pressure 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 Arctic Ocean, leaving the high
Arctic filled with younger and thinner ice, she said.The Arctic Oscillation refers to opposing atmospheric pressure patterns in northern middle and high latitudes. The oscillation exhibits a "negative phase" with relatively high pressure over the polar region and low pressure at mid-latitudes (about 45 degrees North), and a "positive phase"(at right) in which the pattern is reversed. In the positive phase, higher pressure at mid-latitudes drives ocean storms farther north, and changes in the circulation pattern bring wetter weather to Alaska, Scotland and Scandinavia, as well as drier conditions to the western United States and the Mediterranean. In the positive phase, frigid winter air does not extend as
far into the middle of North America as it would during the negative phase of the oscillation. This keeps much of the United States east of the Rocky Mountains warmer than normal, but leaves Greenland and Newfoundland colder than usual. Weather patterns in the negative phase are in general "opposite" to those of the positive phase.Over most of the past century, the Arctic Oscillation alternated between its positive and negative phases. Starting in the 1970s, however, the oscillation has tended to stay in the positive phase, causing lower than normal arctic air pressure and higher than normal temperatures in much of the United States and northern Eurasia.
The end result of a lengthy positive phase of the Arctic Oscillation for the Arctic region 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 polar temperatures drive the jet stream, and in the past couple of decades, there’s been a 20 percent drop in the zonal 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.
Source:
Summit County Citizens Voice,"Global Warming: ‘Revenge of the atmosphere’", by Bob Berwyn, accessed January 17, 2012
Arctic Climatology and Meteorology, "The Arctic Oscillation", accessed January 17, 2012
