BigAlthough the international effort to phase out ozone-depleting substances, the Montreal Treaty, has led concentrations to fall consistently following a peak in the 1990s, the ozone hole they are responsible for creating has a longer period of inertia and can vary unpredictably from year to year.

The Montreal Treaty led to the phasing out of ozone-depleting chemicals such as chlorofluorocarbons (CFCs) found in spray-cans, fridges and air conditioning systems that cause ozone depletion.

Between September 21 and 30 the average area of the ozone hole reached 27.4m square kilometres – an area bigger than the North American continent.

The record depletion, which saw practically all of the ozone gone from the crucial region 8-13 km above the earth’s surface, coincided with extremely high levels of chlorine ozone-depleting chemicals in high atmospheric regions.

“In this critical layer, the instrument measured a record low of only 1.2 DU., having rapidly plunged from an average non-hole reading of 125 DU in July and August,” NOAA said.

David Hofmann of the NOAA Earth System Research Laboratory said: “These numbers mean the ozone is virtually gone in this layer of the atmosphere.

“The depleted layer has an unusual vertical extent this year, so it appears that the 2006 ozone hole will go down as a record-setter.”

The World Meteorological Organization predicted that the ozone hole would fully recover by 2065 in its recently completed Scientific Assessment of Ozone Depletion, with the recovery initially masked by annual variation.

“We now have the largest ozone hole on record for this time of year,” says NOAA’s Craig Long. “As the sun rises higher in the sky during October and November, this unusually large and persistent area may allow much more ultraviolet light than usual to reach Earth’s surface in the southern latitudes.”

More information can be found on the NOAA website.

Goska Romanowicz

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