Go on out and celebrate: the ozone hole is in recovery. For the first time since the 1987 Montreal Protocol banned the use of ozone-destroying chemicals - notably chlorofluorocarbons (CFCs) - scientists have measured an upswing in the level of ozone over Antarctica.

While the party gets going, however, it is worth taking a moment to reflect that the discovery of the hole in the ozone layer was the only thing that mobilised politicians to act. When it comes to global action based on science, only desperate times seem to call for any measures at all.

If scientists want to protect the planet, just publishing the data is not enough. The first practical research evidence of the destructive power of ozone was published in June 1974. It was at once clear, scientifically speaking, that we needed a ban on CFCs, but the science alone couldn't make it happen.

The 13 years that followed were a period of obfuscation, lies and industry-sponsored PR campaigns against those researchers who were most vocal in supporting a ban. Only after they discovered catastrophic environmental damage over the Antarctic - a huge opening through which cancer-causing solar radiation was pouring - did anything change.

It was the same story with uninhibited use of pesticides in America; it was only once the damage to the natural world became too obvious to ignore that the politicians acted. Similarly, the effects of acid rain were felt long after scientists first sounded warnings and long, long before legislation curbed industrial emissions of sulphur dioxide.

Perhaps three precedents will be enough to stop climate change becoming another example, but the scientists involved shouldn't assume anything. Sherwood Rowland, who won a 1995 Nobel prize for his role in making the scientific case for the Montreal Protocol, has cried shame on the passive attitude of scientists.

“What's the use of having developed a science well enough to make predictions," he said, “if, in the end, all we're willing to do is stand around and wait for them to come true?"

Many of Rowland's colleagues ostracised him for his activism. Even James Lovelock called for “a bit of British caution" in the face of his zeal. But right now caution is the last thing we need.

Arrested development

In August, it will be 30 years since the climatologist James Hansen published the first scientific projections of the runaway greenhouse effect. Frustrated by a lack of legislative response in the ensuing decades, he has resorted to activism, repeatedly getting himself arrested at climate-related protests. It is an unusual stance for a scientist to take, especially one who is so senior (Hansen is director of Nasa's Goddard Institute for Space Studies in New York), but it is becoming increasingly necessary, he reckons. History makes it clear that it is not enough for scientists to publish the research; they also need to work to make sure it gets an appropriate response.

According to the UN Environment Programme, the Montreal Protocol has helped prevent up to 20 million additional cases of skin cancer. Left unchecked, global warming would cause much more damage. It would be astonishingly stupid of us to repeat our mistakes and wait for catastrophe to be our motivator yet again.

Michael Brooks will be appearing at the Hay Festival on 1 June