4 October 2011

New ozone hole causes concern

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A hole in the ozone layer has been detected over the Arctic for the first time.
Arctic ozone hole

Ozone in Earth's stratosphere at an altitude of approximately 20 km in mid-March 2011, near the peak of the 2011 Arctic ozone loss. Credit: NASA/JPL-Caltech

Chlorine monoxide

Chlorine monoxide – the primary agent of chemical ozone destruction in the cold polar lower stratosphere – for the same day and altitude. Credit: NASA/JPL-Caltech

DUBLIN: A hole in the ozone layer has been detected over the Arctic for the first time.

An unprecedented loss of ozone occurred during the northern winter of 2011 and this is potentially bad news for human health, according to international team that reported the discovery this week in the journal Nature.

The stratospheric ozone layer extends from about 15 to 35 km above Earth’s surface and protects life from the Sun’s harmful ultraviolet (UV) rays. Depletion of ozone in this layer is associated with higher exposure at the surface to UV, which is known to be associated with adverse health and ecosystem impacts, said co-author Gloria Manney at NASA’s Jet Propulsion Laboratory in Pasadena, California.

Ozone-destroying chemicals

Extremely cold conditions in the atmosphere trigger reactions that transform chlorine into forms that chemically obliterate ozone. The necessary conditions occur every winter in the Antarctic stratosphere, where a hole in the ozone first caused alarm in the mid-1980s, with depletion observed in spring. The chlorine originates from man-made compounds.

Until now, the Arctic winter stratosphere has been much warmer than the Antarctic’s, with conditions of low temperature not persisting for long enough to allow extensive ozone destruction. The cold period in the Arctic stratosphere lasted much longer in late 2010 to early 2011, however, allowing ozone-destroying forms of chlorine to linger and destroy more ozone. A loss of 80% of ozone was observed at an altitude of 18 to 20 km.

The discovery came after analysis of observations from satellite instruments and from balloon-borne ozone sensors. The international team concluded, “For the first time, sufficient loss occurred to reasonably be described as an Arctic ozone hole.”

Unprecedented event

This is the first report of chemical ozone destruction over the Arctic which is comparable to that in the Antarctic ozone hole. No previous year rivals 2011 in the Arctic for the loss of this protective ozone blanket.

Reduced overhead ozone means more UV at the Earth’s surface, which is known to have adverse effects on people. “The Arctic ‘polar vortex’ (the persistent large-scale cyclone within which the ozone loss takes place) does not remain stationary over the pole,” noted Manney, “but often shifts to lower latitudes, sometimes over densely populated regions.” Protection from UV could therefore be severely diminished over northern European countries.

Manney added that because Arctic temperatures vary greatly from year to year, our ability to predict those variations is limited. “The unusually cold period in 2011 was not predicted in advance and we cannot say when such a lingering cold period might occur again in the Arctic.”

The unusual ozone levels likely exposed the Arctic surface to unusually high levels of UV light during spring and early summer, according to co-author Andrew Klekociuk, senior scientist in the Australian Antarctic Division, which could have repercussions for the Arctic climate and ecosystems. “This event tests the ability of state-of-the-art climate models to simulate the observed conditions, and it’s likely that we’ll see improved understanding of the complex interplay between the chemistry and dynamics of the atmosphere as a result as scientists conduct further investigations,” he said.

The other ozone hole

Jonathan Shanklin, head of meteorology and ozone monitoring unity at the British Antarctic Survey, said that future predictions are indeed uncertain, and it is also premature to say that the Antarctic ozone hole is recovering.

“We might yet see the deepest one ever, even though the amount of ozone depleting substances is clearly declining.” Shanklin was part of the team who discovered of the ozone hole in the Antarctic in 1985.

“This year the Antarctic ozone hole is above average size compared to the last decade, though not the largest. Depletion is still continuing and it is too soon to say what the minimum level will be,” Shanklin added.

The British Antarctic Survey said the ozone hole over the South Pole began to form in mid-August, reaching an area of around 24 million square kilometers by mid-September. Over the past few years, the Antarctica ozone hole has extended to parts of Argentina, Chile and the Falkland Islands. With an Arctic ozone hole, a whole new list of countries in the Northern Hemisphere could now be at risk.

Health risks

According to the World Health Organisation, the depletion of ozone negatively affects human health: the incidence of cataracts and skin cancer is increasing and it is probable that the human immune system is being weakened.

Steve Jackson, head of Cancer Research UK Laboratories at the University of Cambridge in England, commented that the depletion of ozone leads to higher levels of UV getting through, “including the most energetic and dangerous forms.” He added that ozone depletion leads to higher levels of DNA damage upon sunlight exposure and this can kill cells or induce mutations that may lead to cancer.

UV light also damages skin in other ways, such as making it look more aged, he said. “Any substantial depletion of the ozone layer could, therefore, lead to higher levels of cancer in people and animals.”

Klekociuk added it is important to note that detailed observations of the Arctic stratosphere have only been available since the late 1970s. “So our knowledge of meteorological variability in this part of the atmosphere is more limited than for the lower atmosphere.”

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