Arctic ozone hits record low.

Ozone depletion over the North Pole reached record proportions this spring, heightening risks of UV-B radiation and sunburn as far south as Italy, according to scientists conducting a five-year assessment of Earth's ozone layer. In April, researchers with Europe's SCOUT-O3 project reported the loss of more than half of all ozone at 18 kilometers above the pole, and destruction of 30 percent of the Arctic's total protective ozone cover.

The team attributes the depletion to cooler winter temperatures--the lowest in 50 years--in the polar stratosphere. Consistently low temperatures can contribute to the formation of large cloud areas in the ozone layer, altering its chemical balance, explained Markus Rex of Germany's Alfred Wegener Institute of Polar and Marine Research. These conditions boost the ozone-destroying properties of chlorine and bromine, chemicals that are released when chlorofluorocarbons (CFCs), halons, and other halogen-containing compounds break down in the presence of sunlight.

Scientists had hoped that the phaseout of these compounds under the 1987 Montreal Protocol would lead to a gradual "healing" of Earth's ozone layer by 2050. However, studies now suggest that a second variable--climate change--may also play a key role in ozone depletion, delaying recovery. Atmospheric build-up of the same greenhouse gases that contribute to global warming may be causing the upper atmosphere to cool, contributing to the enhanced ozone loss. If strong cooling occurs, scientists predict that an ozone "hole" similar to one that has appeared over the South Pole in all but one winter since the late 1980s could appear over the Arctic within two decades.

Without the protection of the ozone layer, humans and animals risk excessive exposure to UV-B radiation, which has been shown to cause skin cancer, eye abnormalities such as cataracts, and changes in the immune system that can make people more susceptible to cancer or infectious disease. UV-B radiation can also damage marine ecosystems and reduce plant and fish yields. Although most ozone loss has occurred above the poles, its effects can eventually be felt in more densely populated areas as the ozone-depleted air masses drift over other regions.

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