Climate change may be causing continued ozone depletion over Arctic

The researchers say one of the coldest stratospheric winters on record has caused a 60% decline in ozone in the stratosphere over the Arctic. They say the cold temperatures could be related to tranquil weather in the lower atmosphere caused by climate change.

The researchers are concerned that climate change may continue to cause the decline of Arctic ozone despite reductions in stratospheric chlorine levels following the implementation of the Montreal Protocol (see related story). Certain forms of chlorine are the main chemicals involved in ozone depletion.

The SAGE III Ozone Loss and Validation Experiment (SOLVE), the largest international campaign ever to investigate stratospheric ozone depletion, observed large ozone losses over the Arctic during the winter of 1999/2000.

The results have reinforced concerns that the recovery of the ozone layer may be slowing down. Possible causes of the stratospheric cooling include increasing concentrations of greenhouse gases, reduced concentrations of ozone in the stratosphere or changes in the dynamics of the stratosphere.

The ozone losses have been blamed on polar stratospheric clouds (PSCs), which can only form in low temperatures. These are directly involved in the conversion of chlorine from benign molecular forms into the chlorine monoxide (CIO) molecule. The CIO molecule is the principal chlorine compound involved in ozone loss.

From January to March, the researchers measured high ClO concentrations along with large PSCs over the Arctic region. On January 28, the stratospheric area covered by temperatures low enough to form PSCs was 14.8 million km2. The total surface area of Europe is just over 10 million km2. The last PSCs were observed around 10 March.