Arctic

Massive ozone hole yawned over Arctic, but Alaska avoided damaging rays

The Arctic experienced its first full-blown ozone "hole" last winter, possibly exposing people in Scandinavia, Russia and Mongolia to elevated levels of ultraviolet radiation, according to a NASA-sponsored study published online this weekend by Nature and warnings issued last spring during the event.

A long-lasting bout of extremely cold temperatures about 12 miles above the frozen polar sea destroyed so much O3 that the Far North temporarily rivaled the Antarctic in the sudden, dramatic depletion of this important trace gas, the scientists said.

"Chemical ozone destruction over the Arctic in early 2011 was -- for the first time in the observational record -- comparable to that in the Antarctic ozone hole," the scientists wrote in the paper. "Unusually long-lasting cold conditions in the Arctic lower stratosphere led to persistent enhancement in ozone-destroying forms of chlorine and to unprecedented ozone loss, which exceeded 80 percent."

When this ozone hole drifted off the North Pole toward portions of Eurasia in April, monitoring stations recorded that elevated levels of ultraviolent radiation started reaching the ground, the scientists warned at the time.

But Alaskans escaped exposure to these elevated rays -- although ozone levels remained high over the state throughout the episode, according to the lead author of the new paper, Gloria Manney, a senior research scientist at NASA's Jet Propulsion Laboratory.

"The Arctic vortex (and thus this year, the "ozone hole") tends to move around quite a lot from day to day, and, indeed, this year tended to be shifted away from Alaska, so that ozone values were typically rather high over your heads," Manney explained in an email to Alaska Dispatch.

But Alaska has no immunity to a future zap. The Arctic vortex -- that ozone-sapping continent-size mass of confined air -- sometimes slips south over the U.S. Far North. If another major Arctic ozone hole forms late next winter and morphs south, Alaskans might face the same elevated UV risk experienced on the other side of the globe.

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Increased UV exposure due to general global ozone thinning has been linked to some health problems, particularly increases in sunburn, cataracts and certain kinds of skin cancer. This new research paper didn't tackle the health impact during the Arctic's hole, Manney said, but UV levels did spike up in Europe.

"More research will be needed to quantify how much the UV was increased and what effect it had on life on the Earth's surface," Manney said.

Polar winters love to eat up the ozone

Ozone is a naturally occurring gas molecule comprised of three oxygen atoms -- the oxygen that we breathe is O2. When spread out in sufficient concentrations across the upper atmosphere six to 31 miles high, ozone helps block up to 99 percent of solar ultraviolent radiation from reaching the Earth's surface.

Scientists say the overall level of ozone has declined during recent decades, mostly due to the release of chlorofluorocarbons by modern civilization. Scientists have long warned that this loss could cause health problems and dangerous cancers. Under the international Montreal Protocol treaty, substances that deplete the ozone are being phased out, with full recovery of the ozone layer possible by 2050.

But there's another factor in the depletion of ozone, the same thing that's been warming the globe the past century: higher concentrations of human-released greenhouse gases like carbon dioxide.

As these gases slow the loss of heat into space, contributing to an increase in the global temperature in the lower atmosphere, they also slow the rise of heat into upper atmosphere. This makes the stratosphere grow colder, triggering a chemical process that eats up polar ozone during late winter and spring.

Thus, an "ozone hole" has formed over Antarctica during austral winter since the 1980s, caused by the same general processes seen last winter in the Arctic. Scientists say the vortex over the Antarctic is larger and more stable than the Arctic version -- and ozone levels in the Arctic typically start the winter at much higher levels.

The Far North had previously experienced declines in ozone during winter, but never such a dramatic loss as the one in 2011.

"For the first time, sufficient loss occurred to reasonably be described as an Arctic ozone hole," the scientists said.

Blame a particularly mean stratospheric cold snap -- 100 degrees below zero Fahrenheit for weeks on end.

"Day-to-day temperatures in the 2010-11 Arctic winter did not reach lower values than in previous cold Arctic winters," explained Manney in this story posted by NASA. "The difference from previous winters is that temperatures were low enough to produce ozone-destroying forms of chlorine for a much longer time."

Ozone alerts issued in Europe, as the 'vortex' oozes south

The startling Arctic ozone depletion surprised scientists last March. An international network of more than 30 ozone measuring stations tracked the ozone loss as it happened, leading to a warning from the Alfred Wegener Institute, Europe's leading Arctic research organization, and the World Meteorological Organization about the potential for exposure in Scandinavia and Central Europe.

"Such massive ozone loss has so far never occurred in the northern hemisphere, which is densely populated even at high latitudes," said researcher Markus Rex, and one of the authors of the current study, in this story about UV exposure.

"Our measurements show that at the relevant altitudes, about half of the ozone that was present above the Arctic has been destroyed over the past weeks," Rex added at the time. "Special attention should thus be devoted to sufficient UV protection in spring."

To investigate why the Arctic lost so much ozone so fast, a team of 29 scientists from 19 organizations in nine countries analyzed a vast array of atmospheric measurements by satellites, weather balloons and ground stations. They included observations of trace gases and clouds by NASA's Aura and CALIPSO spacecraft.

"At some altitudes, the cold period in the Arctic lasted more than 30 days longer in 2011 than in any previously studied Arctic winter, leading to the unprecedented ozone loss," the scientists concluded.

Here's more plain-language analysis from NASA:

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The incident offers a chilling harbinger for the future of Arctic ozone.

"If winter Arctic stratospheric temperatures drop just slightly in the future ... severe Arctic ozone loss may occur more frequently," the scientists wrote here.

Ozone monitoring may be crucial for Alaska, scientist says

It's impossible to know whether another ozone hole will occur next spring, Manney told Dispatch.

"We have, at present, a limited ability to predict more than a week or two in advance what those temperatures may be," Manney said in an email.

As a result, Manney said it's important that the United States and other countries maintain real-time monitoring with satellites and ground operations -- and continue to fight for reductions in ozone depleting chemicals.

For instance, without the Montreal Protocol -- the treaty that limited production and release of chlorine-based chemicals -- an Arctic ozone hole would likely be forming every spring, scientists said.

"It is crucial that we continue to monitor the Arctic stratosphere, both ozone and the other chemicals involved in its destruction," Manney told Dispatch. "By doing so we will be able to see what is happening in any given winter ... and to improve our understanding of the processes involved so that we can learn to predict (ozone holes) farther in advance.

"While important to all of us here on Earth in relation to the overall 'health' of our environment, these issues are of special relevance to anyone living at the higher latitudes, including Alaskans, since they could be personally affected."

Contact Doug O'Harra at doug(at)alaskadispatch.com

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