In 1974, scientists discovered that humans were unintentionally causing ozone depletion — a potential climate disaster. In 1985, when they discovered the Antarctic ozone hole and realized how severe depletion had become, they worked very effectively with political leaders at the United Nations to frame the Montreal Protocol, stopping the increase in depletion.

Today, we face another potential climate disaster — global warming — also thought by many scientists to be unintentionally caused by humans. Why are scientists and political leaders having so much trouble working together today to address a related problem?

Saturday, September 16, is World Ozone Day, celebrating the success of the Montreal Protocol on Substances that Deplete the Ozone Layer, agreed at the United Nations on September 16, 1987, thirty years ago. The Montreal Protocol was ratified by all nations on Earth and took effect January 1, 1989.

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By 1993, concentrations in the atmosphere of the manufactured gases that caused the problem stopped increasing. Ten years later, former UN Secretary General Kofi Annan said "perhaps the single most successful international agreement to date has been the Montreal Protocol."

In the 1960s, chlorofluorocarbon gases (CFCs) became very popular for use as spray-can propellants, refrigerants, solvents and foam-blowing agents because they were very inert — they did not interact chemically with most other substances. By 1970, you could buy almost anything in a spray can.

In 1974, however, Mario Molina and F. Sherwood Rowland published a scientific paper showing that CFCs high in the stratosphere could be broken down chemically, releasing atoms of chlorine. One tiny atom of chlorine in the lower stratosphere can destroy 100,000 molecules of ozone.

This was a big surprise, for which they, together with Paul Crutzen, received the Nobel Prize in Chemistry in 1995. The Nobel citation called the ozone layer “the Achilles heel of the biosphere.” Humans had stumbled onto a small way to affect big changes in climate.

The ozone layer acts as an atmospheric shield, protecting life on Earth against harmful ultraviolet-B solar radiation (UV-B). UV-B is so energetic that when it reaches Earth, it causes sunburn, skin cancer and cataracts. UV-B also damages phytoplankton, critical to the aquatic food web, and damages crops on land. On the other hand, UV-B helps our bodies produce vitamin-D, something we must have for developing strong bones.

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In the 1970s, producers of CFCs argued the science was flawed, even calling it “utter nonsense.” Intensive new research, however, led to a report by the National Academy of Science in 1976 confirming the scientific credibility of the ozone depletion hypothesis.

By 1985, when the Antarctic ozone hole was discovered, industry was still arguing the science was faulty, but most atmospheric chemists had concluded that CFCs were the primary cause of ozone depletion and that damage already done was significant. There were now substitutes for CFCs manufactured by the same companies and mandating cutbacks in production of CFCs was relatively inexpensive.

Within two short years, the Montreal Protocol was crafted and agreed to.

Sure enough, by 1993 the increases in CFC concentrations in the atmosphere stopped. By 1995, the increases in ozone depletion stopped. By 1998, the increases in global temperatures stopped.

Humans had not only depleted the ozone layer, they appear to have caused the major increase in global warming from 1970 to 1998. Had it not been for the Montreal Protocol, global temperatures today might have been almost another degree warmer. When ozone is depleted, less UV-B is absorbed by the ozone layer and more UV-B is observed to reach Earth, causing global warming.

With the success of the Montreal Protocol, many scientists, convinced that increases in concentrations of greenhouse gases must be the primary cause of global warming, encouraged the United Nations to set up the Intergovernmental Panel on Climate Change (IPCC) to develop scientific consensus behind greenhouse-warming theory so that political leaders would mandate cutbacks in greenhouse-gas emissions. With negotiation of the Paris Agreement in December, 2015, their efforts seemed to have paid off.

The problem is that greenhouse-gases are produced by humans primarily when burning fossil fuels, which provide the vast majority of energy used to drive our economy and our quality of life.

While initial estimates for implementing the Paris Agreement are in the trillions of dollars, many leading scientists question whether the Paris Agreement is too little, too late. The potential damage to global economies could be catastrophic.

Meanwhile, the relentless drive for consensus, led by the IPCC, discouraged scientific debate. Consensus is the stuff of politics, but debate is the stuff of science. Science is never settled.

There are always new observations and data challenging established ideas. Perhaps the greatest strength of science is that over time, science is self-correcting. But as the climate wars have raged on, scientists have become more and more defensive of their “consensus.” Their worst nightmare is that there could be any problem with greenhouse-warming theory and that those not supporting greenhouse-warming theory might be right for the wrong reasons.

There is now considerable evidence that greenhouse-gases cannot be to primary cause of global warming. We need to bring back genuine scientific debate. Not red team/blue team arguments along the same battle-weary lines of evidence. We need to step back, note the primary role that ozone depletion appears to have played in warming the world from 1970 to 1998 and that the Montreal Protocol appears to have stopped this warming for more than 15 years.

Warming since 2014 has increased 5-times faster than warming from 1970 to 1998, apparently due to ozone depletion caused by the eruption of Bárðarbunga volcano in Iceland, the highest rate of extrusion of basaltic lava since 1783. Such large flows of basaltic lava are associated with major warming throughout Earth history. Yes, global warming has been occurring sporadically throughout Earth history and the mechanism appears similar to that caused by man. Volcano-caused ozone depletion only lasts for years, while CFC-caused ozone depletion lasts for decades.

The problem today is that the science is by no means as clear as at the time of the Montreal Protocol and the proposed costs of taking action are much greater. Can we build on the success of the Montreal Protocol learning how to reduce ozone depletion caused by man and learning how best to adapt to ozone depletion caused by nature?

Peter L. Ward worked 27 years with the United States Geological Survey. He was the chairman of the White House Working Group on Natural Disaster Information Systems during the Clinton administration. He’s published more than 50 scientific papers. He retired in 1998 but continues working to resolve several enigmatic observations related to climate change. His work is described in detail at WhyClimateChanges.com and in his book What Really Causes Global Warming? Greenhouse gases or ozone depletion?Follow him on Twitter at @yclimatechanges.