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‘Mini-Holes’ have opened in the ozone layer over northern Europe and
Canada in the past few weeks. But, according to Joe Farman of the British
Antarctic Survey’s ozone secretariat, they are ‘if anything, more transitory
and less deep than last year’.

In recent years the ozone layer has thinned over both the Arctic and
Antarctic each spring. But the Arctic has yet to suffer the deep, widespread
and sustained ozone loss seen each year over Antarctica. Press reports last
weekend revealed that, locally and for short periods, ozone levels in the
upper atmosphere fell during the past month to between 10 and 40 per cent
below normal as far south as Shetland.

March is the most dangerous month for the Arctic ozone layer, as the
solar radiation that drives ozone-destroying chemical reactions increases
after the long winter. But much depends on local meteorology. The formation
of large areas of high pressure in the lower atmosphere both lowers ozone
levels, by squeezing the ozone layer above, and may provide the very cold
conditions in which ozone destruction is greatest.

‘We really know very little about what could happen in the next month,’
says Farman.