The ozone, a gas made of three oxygen atoms, forms a protective shield against the UVB streaming towards the Earth in the Sun's rays. We know that high levels of UVB cause non-melanoma skin cancers and there is solid evidence UVB radiation can damage wild plants, crop plants and plankton in the sea - all of them at the base of food chains.
So is mankind's damage to the tenuous ozone layer, caused by chlorofluorocarbons and other industrial compounds, actually allowing more UVB to reach the Earth's surface? And what harm is being done?
The answer to the first question is yes, but there is no clear answer to the second, so far. Fortuitously, the worst ozone destruction seen to date takes place in places and at a times of the year when it is least likely to do damage - in the springs of both the southern and northern hemispheres and in the unpopulated polar regions.
Nonetheless, University of California scientists have reported that in the Antarctic extra UVB pouring through its ozone hole knocks back the plankton. Ozone-depleted air has also drifted over the populated tip of South America.
Marked ozone depletion takes place over the Arctic, too, allowing more UVB to reach populated zones such as Scandinavia, Alaska and northern Russia and Canada - and, over the past few days - Britain.
But, from a human point of view, winter is the best time for this to happen. The Sun is low in the sky, it is often cloudy, people spend most of their time indoors and when they do go out they are usually wrapped up.People get exposed to much more UVB in summer, irrespective of ozone damage.
But scientists, including Colin Driscoll, head of the optical radiation group at the Government's National Radiological Protection Board, say that ozone depletion is a real concern. Any pollution which changes the global atmosphere letting through harmful radiation has to be taken seriously.
The ozone layer should begin to repair itself around 2000, thanks to international treaties curbing CFCs and other chemicals. But it will not be until the middle of the next century when the Antarctic ozone holes, the largest to date, disappear.Reuse content