That treaty is known, in shorthand, as the Montreal Protocol. Its formal purpose is to save the ozone layer in the upper atmosphere, which protects the planet and its people from debilitating levels of cancer-causing ultraviolet radiation.
The negotiations on behalf of the United States, in the 1980s, were carried out by the Reagan administration. And the treaty is turning out to be one of the more momentous steps Ronald Reagan took as president.
The Montreal Protocol is widely seen as the most successful global environmental treaty. It incorporates pragmatic, business-friendly principles that have allowed it to operate smoothly for more than two decades, achieving its goals — and then some — with little controversy.
To those paying attention, all of that has been known for years. Now comes a new piece of science, though, saying that the treaty may be even more important in limiting global warming than we thought. It is a timely paper, since a proposal is on the table to rejigger the treaty in a way that could help us still more in slowing the rate of climate change.
The story began in the 1970s when two scientists working together in California, Mario J. Molina and F. Sherwood Rowland, realized that a commonly used group of industrial chemicals posed a frightening hazard. The chlorofluorocarbons, used in refrigerators and air-conditioners and as propellants in products like hair spray, were drifting into the upper atmosphere and breaking down in ways that were thinning the ozone layer.
In short, Dr. Molina and Dr. Rowland had discovered a global environmental emergency. Continued use of the chemicals threatened society with huge increases in skin cancer, damage to crops and many other problems.
The work would eventually merit the Nobel Prize, but that did not prevent a tortuous political battle over the issue. Some of the same people who deny global warming now took money from the chemical industry back then to challenge the science. But the stunning announcement by British scientists in 1985 that an actual hole in the ozone layer had appeared over Antarctica caught the public imagination in a way few scientific discoveries do, ramping up the demands for action.
Mr. Reagan, with his zeal for deregulation and his conservative business principles, might have been expected to fight the idea of a global treaty. That is exactly what many of his closest aides wanted him to do. In the end, he rejected their advice and backed it, vigorously.
Why? One idea is that Mr. Reagan himself had had skin cancer, and allowed a concern for public health to triumph over ideology. Eli Lehrer, the head of a Washington think tank called the R Street Institute and a longtime Reagan admirer, offered me a simpler theory: that the man truly loved nature. He was never happier than when riding horses and chopping wood. Perhaps the science of the ozone hole just spooked him. We know it spooked Margaret Thatcher, the British prime minister and Reagan ally, who had been a research chemist in her early life.
The Montreal Protocol on Substances That Deplete the Ozone Layer entered into force on Jan. 1, 1989, and in the years since, it has been used to phase out nearly 100 dangerous gases.
Now, the wheel of history often turns on chance, and here is one of the great coincidences of our time: Many of the substances that destroy the ozone layer also happen to be exceedingly powerful greenhouse gases.
If production had been allowed to continue, a batch of scientific studies show, the planet would most likely be warming a lot faster than it is. The latest of these studies came out only a few weeks ago. Led by Francisco Estrada of the Autonomous National University of Mexico, the paper suggests that the slowdown in global warming that has occurred over the past 15 years is a direct result, at least in part, of the success of the Montreal Protocol.
In fact, the evidence suggests the protocol has done far more to limit global warming than the better-known treaty adopted for that purpose, the Kyoto Protocol.
Could it do still more?
It turns out the gases phased out under the Montreal Protocol are being replaced by another set of chemicals, hydrofluorocarbons. They do not destroy the ozone layer, but they are potent at causing global warming.
Prodded by small island countries concerned about drowning on a warming planet, nations are considering an amendment to the Montreal Protocol that would phase out the worst chemicals in this group in favor of new ones that are safer for the climate.
For years, big developing countries have been holding out, for they have important industries tied to hydrofluorocarbons. But China came on board over the summer, and the Obama administration is cajoling the last big holdout, India, at this very moment.
It seems to be a matter of time before the deal gets done, and if it does, the projections say we will gain substantial climate benefits this century. Once again, amid all the paralysis over climate change, the Montreal Protocol will have proved to be the little treaty that could.
Durwood Zaelke, who heads a Washington advocacy group called the Institute for Governance and Sustainable Development that is pushing for the treaty amendment, told me he drew a simple lesson from all this: However overwhelming global warming may seem at times, we are not powerless in the face of it.
A persistent claim made by believers in man-made global warming – they were at it again last week – is that no politician was more influential in launching the worldwide alarm over climate change than Margaret Thatcher. David Cameron, so the argument runs, is simply following in her footsteps by committing the Tory party to its present belief in the dangers of global warming, and thus showing himself in this respect, if few others, to be a loyal Thatcherite.
The truth behind this story is much more interesting than is generally realised, not least because it has a fascinating twist. Certainly, Mrs Thatcher was the first world leader to voice alarm over global warming, back in 1988, With her scientific background, she had fallen under the spell of Sir Crispin Tickell, then our man at the UN. In the 1970s, he had written a book warning that the world was cooling, but he had since become an ardent convert to the belief that it was warming, Under his influence, as she recorded in her memoirs, she made a series of speeches, in Britain and to world bodies, calling for urgent international action, and citing evidence given to the US Senate by the arch-alarmist Jim Hansen, head of Nasa's Goddard Institute for Space Studies.
She found equally persuasive the views of a third prominent convert to the cause, Dr John Houghton, then head of the UK Met Office. She backed him in the setting up of the UN's Intergovernmental Panel on Climate Change (IPCC) in 1988, and promised the Met Office lavish funding for its Hadley Centre, which she opened in 1990, as a world authority on "human-induced climate change".
Hadley then linked up with East Anglia's Climatic Research Unit (CRU) to become custodians of the most prestigious of the world's surface temperature records (alongside another compiled by Dr Hansen). This became the central nexus of influence driving a worldwide scare over global warming; and so it remains to this day – not least thanks to the key role of Houghton (now Sir John) in shaping the first three mammoth reports which established the IPCC's unequalled authority on the subject.
In bringing this about, Mrs Thatcher played an important part. It is not widely appreciated, however, that there was a dramatic twist to her story. In 2003, towards the end of her last book, Statecraft, in a passage headed "Hot Air and Global Warming", she issued what amounts to an almost complete recantation of her earlier views.
She voiced precisely the fundamental doubts about the warming scare that have since become familiar to us. Pouring scorn on the "doomsters", she questioned the main scientific assumptions used to drive the scare, from the conviction that the chief force shaping world climate is CO2, rather than natural factors such as solar activity, to exaggerated claims about rising sea levels. She mocked Al Gore and the futility of "costly and economically damaging" schemes to reduce CO2 emissions. She cited the 2.5C rise in temperatures during the Medieval Warm Period as having had almost entirely beneficial effects. She pointed out that the dangers of a world getting colder are far worse than those of a CO2-enriched world growing warmer. She recognised how distortions of the science had been used to mask an anti-capitalist, Left-wing political agenda which posed a serious threat to the progress and prosperity of mankind.
In other words, long before it became fashionable, Lady Thatcher was converted to the view of those who, on both scientific and political grounds, are profoundly sceptical of the climate change ideology. Alas, what she set in train earlier continues to exercise its baleful influence to this day. But the fact that she became one of the first and most prominent of "climate sceptics" has been almost entirely buried from view.