The inability of governments to formulate a common strategy against global warming gives the impression that even severe threats cannot get the world's nations working together. A joint UN and World Meteorological Organisation study's findings that the earth's ozone layer is showing early signs of thickening say otherwise. The protective shield against cancer-causing ultraviolet rays was thinning and shrinking until political determination forced the phasing out of the man-made gases that destroy ozone. It is cause for optimism that even greater challenges can be dealt with.

Scientists began warning in the late 1970s that mounting damage to the ozone layer was behind rising levels of skin cancer and was damaging eyesight, immune systems, wildlife and agriculture. The culprit was ozone-harming chemicals, including chlorofluorocarbons, commonly called CFCs, then widely used in spray cans and refrigerators. Under the UN, the chemicals were banned under the 1986 Montreal Protocol. The UN had predicted that without the pact, there would have been an extra two million skin cancer cases a year by 2030.

Global warming is a substantially bigger threat. It is behind rising sea levels, extreme weather and warmer oceans. Crops, fresh water, wildlife and ways of life are being endangered. Yet the nations most behind the pollution that causes the rise in temperatures cannot agree a common approach, preferring to take their own measures. Ironically, the good news on the ozone layer was accompanied by bad news on global warming; levels of atmospheric greenhouse gases are at a record high.