Dr Solomon said the ozone hole over Antarctica, and lesser ozone depletions over the Arctic, have now established a pattern in which vortices of extremely cold air are becoming trapped over the polar regions instead of performing their natural function of spreading to lower latitudes and cooling global weather systems.

Dr Solomon led the 1986-87 research expedition to Antarctica that proved that chlorofluorocarbons, or CFCs, in aerosol sprays were accumulating above the poles and driving a complex chemical chain reaction that destroyed the ozone layer in the upper atmosphere.

After hearing from Dr Solomon and other researchers, some delegates said they would advise their governments that the option of waiting for more evidence of climate change was being overtaken by the real thing. Outbreaks of extreme weather would take an unacceptable toll of human life, farm production and social infrastructure, including transport systems and buildings.