Wynne Parry LiveScience.com Yahoo News 3 Oct 11;
The high atmosphere over the Arctic lost an unprecedented amount of its protective ozone earlier this year, so much that conditions echoed the infamous ozone hole that forms annually over the opposite side of the planet, the Antarctic, scientists say.
"For the first time, sufficient loss occurred to reasonably be described as an Arctic ozone hole," write researchers in an article released Oct. 2 by the journal Nature.
Some degree of ozone loss above the Arctic, and the formation of the Antarctic ozone hole, are annual events during the poles' respective winters. They are driven by a combination of cold temperatures and lingering ozone-depleting pollutants. [North vs. South Poles: 10 Wild Differences]
The reactions that convert less reactive chemicals into ozone-destroying ones take place within what is known as the polar vortex, an atmospheric circulation pattern created by the rotation of the Earth and cold temperatures. This past winter and spring saw an unusually strong polar vortex and an unusually long cold period.
This year's record vortex persisted over the Arctic from December to the end of March, and the cold temperatures extended down to a remarkably low altitude, the researchers write.
At altitudes of about 11 to 12 miles (18 to 20 kilometers), more than 80 percent of the ozone present in January had been chemically destroyed by late March.
The same dynamics create the infamous ozone hole over Antarctica. But above the South Pole, ozone is essentially completely removed from the lower stratosphere ever year. Above the North Pole, however, ozone loss is highly variable and has, until now, been much more limited, writes the international research team led by Gloria Manney of the California Institute of Technology.
Countries agreed to end their production of the substances ultimately responsible for destruction of the ozone in 1987 with the Montreal Protocol. However, these pollutants, including chlorofluorocarbons, still linger in the atmosphere. Ozone loss is expected to improve in the coming decades as atmospheric levels of these chemicals decline.
On the Earth's surface, ozone is a pollutant, but in the stratosphere it forms a protective layer that reflects ultraviolet radiation back out into space. Ultraviolet rays can damage DNA and lead to skin cancer and other problems.
Global warming is implicated in the loss of Arctic ozone because greenhouse gases trap energy lower down, heating up the atmosphere nearer the ground but cooling the stratosphere, creating conditions conducive to the formation of the reactive chemicals that break apart the three-oxygen molecules of ozone.
Scientists worried as Arctic has record ozone loss
AFP Yahoo News 3 Oct 11;
An ozone hole five times the size of California opened over the Arctic this spring, matching ozone loss over Antarctica for the first time on record, scientists said on Sunday.
Formed by a deep chill over the North Pole, the unprecedented hole at one point shifted over eastern Europe, Russia and Mongolia, exposing populations to higher, but unsustained, levels of ultra-violet light.
Ozone, a molecule of oxygen, forms in the stratosphere, filtering out ultraviolet rays that damage vegetation and can cause skin cancer and cataracts.
The shield comes under seasonal attack in both polar regions in the local winter-spring.
Part of the source comes from man-made chlorine-based compounds, once widely used in refrigerants and consumer aerosols, that are being phased out under the UN's Montreal Protocol.
But the loss itself is driven by deep cold, which causes water vapour and molecules of nitric acid to condense into clouds in the lower stratosphere.
These clouds in turn become a "bed" where atmospheric chlorine molecules convert into reactive compounds that gobble up ozone.
Ozone loss over the Antarctic is traditionally much bigger than over the Arctic because of the far colder temperatures there.
In the Arctic, records have -- until now -- suggested that the loss, while variable, is far more limited.
Satellite measurements conducted in the 2010-2011 Arctic winter-spring found ozone badly depleted at a height of between 15 and 23 kilometres (9.3 and 14.3 miles).
The biggest loss -- of more than 80 percent -- occurred between 18 and 20 kms (11.25 and 12.5 miles).
"For the first time, sufficient loss occurred to be reasonably be described as an Arctic ozone hole," says the study, appearing in the British science journal Nature.
The trigger was the polar vortex, a large-scale cyclone that forms every winter in the Arctic stratosphere but which last winter was born in extremely cold conditions, Gloria Manney, of the Jet Propulsion Laboratory in California, told AFP in email.
"The ozone destruction began in January, then accelerated in late February and March, so that ozone values in the polar vortex region were much lower than usual from early March through late April, after which the polar vortex dissipated.
"Especially low total column ozone values (below 250 Dobson Units) were observed for about 27 days in March and early April.
"The maximum area with values below 250 Dobson Units was about two million square kilometres (772,000 square miles), roughly five times the area of Germany or California."
This was similar in size to ozone loss in Antarctica in the mid-1980s.
In April, the vortex shifted over more densely populated parts of Russia, Mongolia and eastern Europe for about two weeks.
Measurements on the ground showed "unusually high values" of ultra-violet, although human exposure was not constant as the vortex shifted location daily before eventually fading, said Manney.
The study, published by the journal Nature, challenges conventional thinking about the Arctic's susceptibility to ozone holes. This thinking is based on only a few decades of satellite observations.
Stratospheric temperatures in the Arctic have been extraordinarily varied in the past decade, the paper notes. Four out of the last 10 years have been amongst the warmest in the past 32 years, and two are the coldest.
In the stratosphere, ozone is protective. At ground level, where it is produced in a reaction between traffic exhaust and sunlight, it is a dangerous irritant for the airways.
