A mode for global action.

Byline: The Register-Guard

The script is familiar: Scientists warn that human activity is causing an environmental problem with severe worldwide consequences. It's predicted that fixing the problem will be disruptive and expensive.

Developing nations blame the industrialized world for having created the problem and balk at assuming responsibility for corrective action. Developed nations worry that the problem can't be addressed without a broad global commitment. Overlying everything is a cloud of doubt about the cause of the problem, its severity and the effectiveness of the prescribed remedies.

Global warming? Well, yes. But the same type of debate occurred in the 1980s when atmospheric scientists found that a widely used class of chemicals was damaging the Earth's protective ozone layer.

Diplomats, environmentalists and scientists are gathered in Montreal this week to celebrate the success of a treaty signed in that city 20 years ago that set ambitious ozone-protection goals. The Montreal Protocol is encouraging evidence that the nations of the world can pull together in support of a common goal.

The Montreal Protocol eventually was signed by 191 nations. Production of ozone-damaging chlorofluorocarbons, or CFCs, has been reduced in developed nations by 95 percent. Less developed nations have cut their CFC use by more than half.

Despite predictions to the contrary, effective and economical ozone-safe substitutes for CFCs, which were widely used in refrigeration and as aerosol propellants, have been introduced.

The ozone layer in the Earth's stratosphere filters the sun's ultraviolet-B radiation, which can cause skin cancer and cataracts and harm plants and animals. CFCs drift into the Earth's high atmosphere and break down ozone molecules.

In 1985, a seasonal "hole" in the ozone layer was detected over Antarctica, and the ozone layer above North America was found to have been depleted by 7 percent.

CFCs are long-lasting chemicals that will continue to attack the ozone layer for a century or longer. Last year's Antarctic ozone hole was the biggest ever. But the levels of ozone-destroying chemicals in the atmosphere are declining, and the depletion of the ozone layer over North America has been reversed. The Environmental Protection Agency estimates that in the United States alone, the Montreal Protocols will prevent 6.3 million deaths from skin cancer and save $4.2 trillion over a 175-year period.

Global warming is a huge, complicated problem. Its primary human cause is the combustion of the fossil fuels that power modern industrial civilization.

But ozone depletion looked like a tough problem, too. In retrospect, it's surprising how easy it was to make solid, worldwide progress in a relatively brief period.