March 14, 2014
Steve Vavrus was watching intently as an unusually large cyclone formed over the Arctic Ocean in August 2012.
“That cyclone of 2012 was fortuitous,” says Vavrus, an atmospheric scientist at UW-Madison and a faculty associate of the Nelson Institute’s Center for Climatic Research. “I’d started my Arctic cyclone project and was already interested in the topic, so it just happened to coincide with the timing of my research.”
August isn’t normally a prime time for Arctic storms, but the 2012 cyclone lasted more than twice as long as the average, and set records for strength. That was consistent with Vavrus’s research. He’s found that strong Arctic cyclones are happening more frequently and are becoming more intense through time, and he suspects that loss of sea ice is to blame.
Steve Vavrus
Sea ice is mostly white, so it reflects much more light energy than the dark open ocean, which captures and stores heat energy. It also acts as an insulator, isolating the cold atmosphere from the warmer ocean.
“Let’s say that you’re somewhere in the present day that has an ice pack,” Vavrus explains. “It’s very hard to get the ocean’s heat energy through it to the atmosphere. If you remove sea ice, like we think will happen with climate change, then suddenly you’ve got a huge source of heat and moisture energy.”
Heat and moisture fuels storms, especially in the Arctic winter. When the atmosphere cools in October, November and December, the temperature of the deep, dark ocean is slow to catch up. Vavrus says that Arctic cyclones are most often severe in these months because the difference in temperature between the atmosphere and ocean is at its peak. Sea ice usually mediates the effect by keeping a lid on the ocean’s moisture.
But sea ice is retreating as the average global temperature goes up. So a greater area of relatively warm open water is being exposed to the cold atmosphere, and more heat energy and moisture is being released into the system. Vavrus suspects this is causing more severe storm patterns in the Arctic.
Atmospheric scientists use computer models to test these types of phenomena, simulating past or future climate occurrences under a range of variables, such as carbon dioxide levels or vegetative cover, and then comparing the outputs against historical data.
Vavrus looked at barometric pressure – the downward force exerted by air – as an indicator of increasing storms, and examined its relation to loss of sea ice.
“One of the typical features of climate model projections of the future is that sea level [barometric] pressure will decrease in the Arctic,” says Vavrus. “The sign of the change, the trend in the past, is consistent with the type of response we expect from greenhouse warming.”
Barometric pressure is expected to decrease as the Arctic warms, because warm air rises and has low density, counteracting downward pressure.
And low barometric pressure is a sign of storms. Air from higher-pressure systems rushes to fill low-pressure systems, creating high winds; then precipitation occurs as the air rises.
cyclones, more wind, and
more waves, with more open
water, then it can be a double
whammy and really aggravate
the problem of coastal erosion.”
Vavrus studied more than a century’s worth of past barometric pressure readings to infer the presence and strength of past Arctic storms. His findings, published recently in the journal Geophysical Research Letters, show that as the record moved closer to the present, more days with abnormally low barometric pressure occurred, and the low pressure readings became lower.
However, Vavrus cautions that scientists need more data before they can predict the effects of climate change on future polar cyclones.
“The big question that people want to know is, ‘As the Arctic changes in the future more than it has in the past, what impact will that have on storminess?’” Vavrus says. “And I really just scratched the surface of that question.”
But because Vavrus has found a link between climate change and increased polar cyclone activity through time, he believes it’s likely that strong Arctic cyclones will become more intense as the Earth warms. They could also aggravate coastal erosion, a growing concern in the Arctic that has been attributed to a reduction in ice cover.
“If you have a big icepack along the coastline, you probably won’t get as much wave action,” Vavrus explains. “But as the ice pack retreats, there’s going to be more exposed open water, and more wave action. So that alone will favor more coastal erosion.
“What’s new with this study,” he continues, “is that if we get more extreme cyclones, more wind, and more waves, with more open water, then it can be a double whammy and really aggravate the problem of coastal erosion.”
Donald Radcliffe is a forest science and life sciences communication double major who is also pursuing the environmental studies certificate.
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