In the early 1970s, scientists discovered the first human threat to the Earth’s atmosphere — the threat from chlorofluorocarbons, or CFCs, to the stratospheric ozone layer.

The ozone layer shields plants and animals, including humans, from deadly ultraviolet radiation. If the ozone layer were depleted as a consequence of human activities, millions of Americans would develop skin cancer and U.S. health care costs would reach several trillion dollars later this century. Worldwide it would be a catastrophe.

The CFC story started in 1974 with the publication by Mario Molina and F. Sherwood Rowland of their conclusion that CFCs were migrating to the upper atmosphere and destroying the ozone layer. The conclusion was initially disputed by industry, but later empirical evidence showed beyond doubt the destruction of the ozone layer. It also showed that the Antarctic ozone hole was caused by CFCs and related chemicals, a dramatic event that helped galvanize political action. The magnitude of the ozone loss was so unexpected that scientists originally thought their instruments were faulty.

But political action to protect the ozone layer started even before the Antarctic ozone hole was discovered, as citizen consumers in the United States, Canada and Europe acted voluntarily to boycott the ubiquitous spray cans — an average of 15 cans in every household — that used CFCs as propellants for hair spray, deodorants and many other products.

National laws came next, followed by a successful effort to develop an international treaty, the Montreal Protocol, in 1987. The Montreal Protocol parties agreed to cut 50 percent of the first group of CFCs and related chemicals within 12 years. At the next two annual meetings the parties were confident that they could do better and agreed to increase the reduction to 75 percent, and then 100 percent of CFCs, and to move their deadline to 10 years rather than the original 12 years. We saw how success truly breeds success.

The Montreal Protocol commemorates its 25th anniversary of enactment this month, and has reason to celebrate: It has reduced nearly 100 damaging chemicals by nearly 100 percent. Because these same chemicals that destroy the ozone layer also warm the climate, the Montreal Protocol also has made a tremendous contribution to climate protection, nearly 20 times as much as the Kyoto Protocol. This is a planet-saving treaty, protecting both the ozone layer and the climate system. And it can do still more.

This starts with the pending proposals to use the Montreal Protocol to phase down production and use of hydrofluorocarbons, or HFCs, that have high global warming impact. HFCs do not destroy the ozone layer, but some of them are super greenhouse gases that are now being used as substitutes for CFCs and the other chemicals being phased out under the Montreal Protocol. Because of the growing demand for air conditioning and refrigeration in a warming world, HFCs are the fastest growing climate warmer in the United States and elsewhere, growing globally at 10 to 15 percent per year [pdf].

The first proposal to do this was made by low-lying islands, led by the Federated States of Micronesia. This was soon followed by a similar proposal from the United States, Mexico and Canada.

Today, 108 countries have expressed [pdf] their support in a declaration under the Montreal Protocol. If they can overcome opposition from China and India, where most of the future growth in the high impact HFCs will occur, the Montreal Protocol will be able to provide what is a truly significant climate mitigation in the short-term, providing an essential complement to the mitigation we must achieve from reducing carbon dioxide emissions, the key climate pollutant controlling the Earth’s long-term temperature.

If India and China prevent the majority of Montreal Protocol parties from moving forward, the world will miss a vital opportunity to provide near-term climate mitigation and to significantly slow the rate of warming.

A more fitting culmination of 25th year of the world’s most successful environmental treaty would be an agreement to phase down the high-impact HFCs when the parties meet later this year, and again provide broader political momentum for additional action to address the accelerating impact of climate change.

Mario Molina, who shared the Nobel Prize in Chemistry in 1995 for his work on chlorofluorocarbons in the atmosphere, teaches at the University of California, San Diego. Durwood Zaelke is president of the Institute for Governance and Sustainable Development in Washington and Geneva.

This piece also ran online on The Hill’s Congress Blog.