ESA’s Envisat satellite has measured record low levels of ozone over the Euro-Atlantic sector of the northern hemisphere during March. The record low is caused by unusually strong winds, known as the polar vortex, which isolated the atmospheric mass over the North Pole and prevented it from mixing with air in the mid-latitudes. This led to very low temperatures and created conditions similar to those that occur every southern hemisphere winter over the Antarctic.

Scientists are investigating why the 2011 and 1997 Arctic winters were so cold and whether these random events are statistically linked to global climate change. "In a changing climate, it is expected that on average stratospheric temperatures cool, which means more chemical ozone depletion will occur," said Mark Weber from the University of Bremen.

"On the other hand, many studies show that the stratospheric circulation in the northern hemisphere may be enhanced in the future and, consequently, more ozone will be transported from the tropics into high latitudes and reduce ozone depletion."

Answering this question requires more research on ozone modelling and ozone trend monitoring, which is only possible because of the historic satellite data on record.

Source: European Space Agency – Full article www.esa.int/esaCP/SEMIF24SZLG_index_0.html