Ozone loss over the Arctic has reached a record level this spring due to the continuing presence of ozone-depleting substances in Earth's atmosphere and extremely cold temperatures in the stratosphere, the World Meteorological Organization announced on Tuesday.
Even though this Arctic winter was warmer than average at ground level, it was colder in the stratosphere than for a normal Arctic winter, the WMO says. Just above the atmospheric layer closest to Earth, known as the troposphere, the stratosphere starts at an altitude of about 10 kilometers (six miles) and reaches up to an altitude of about 50 km (30 miles).
Observations from the ground and from balloons over the Arctic region as well as from satellites show that the Arctic region has suffered an ozone column loss of about 40 percent from the beginning of the winter to late March, the UN weather and climate agency says.
The highest loss previously recorded was about 30 percent over the entire winter.
"The Arctic stratosphere continues to be vulnerable to ozone destruction caused by ozone-depleting substances linked to human activities," said WMO Secretary-General Michel Jarraud.
"The degree of ozone loss experienced in any particular winter depends on the meteorological conditions. The 2011 ozone loss shows that we have to remain vigilant and keep a close eye on the situation in the Arctic in the coming years," he said.
In Antarctica the ozone hole is an annually recurring winter-spring phenomenon due to the existence of extremely low temperatures in the stratosphere.
In the Arctic the meteorological conditions vary much more from one year to the next and the temperatures are always warmer than over Antarctica. Some Arctic winters experience almost no ozone loss, whereas cold stratospheric temperatures in the Arctic lasting beyond the polar night can lead to substantial ozone loss.
This year, northwest Russia and parts of Scandinavia were under an ozone hole on April 5, protected from harmful ultraviolet radiation by less than 200 Dobson Units of ozone.
Jarraud notes that the record ozone loss has occurred despite the success in cutting production and consumption of ozone-destroying chemicals chalked up by governments under the Montreal Protocol on Substances that Deplete the Ozone Layer.
Substances such as chlorofluorocarbons (CFCs) and halons, once present in refrigerators, spray cans and fire extinguishers, have been phased out under the protocol. "Without the Montreal Protocol, this year`s ozone destruction would most likely have been worse," the WMO said in a statement. "The slow recovery of the ozone layer is due to the fact that ozone-depleting substances stay in the atmosphere for several decades."
