“Government interventions are problematic, so intervene only when the case is fully proven.”
– Margaret Thatcher, Statecraft: Strategies for a Changing World. New York: HarperCollins, 2002, p. 453.
“An Inconvenient Truth About Margaret Thatcher: She Was a Climate Hawk,” declares Will Oremus in Slate. In “The Iron Lady’s Strong Stance on Climate Change” (Daily Climate, reposted at Climate Progress), author Douglas Fischer notes “how seriously [Margaret Thatcher] viewed the threat of climate change and the robustness, more than 20 years ago, of climate science and United Nations body tasked with assessing state of that science.”
True, UK Prime Minister Thatcher was the first and most important international figure to champion the cause of climate alarmism. But the above authors conveniently stop their discussion with her pronouncements in the early 1990s. For possessing an open mind, and coming to see the climate propaganda machine in action, she changed her mind quickly and completely. And the last 20 years gave her little reason to doubt her skepticism.
Early Alarmism (1988–93)
Thatcher “broke quite new political ground,” in her words, by “speaking ominously on climate change to the Royal Society (U.K. Academy of Science) in September 1988, just several months after James Hansen’s U.S. Senate testimony on the same subject. 
“It is possible … we have unwittingly begun a massive experiment with the system of this climate itself,” she said.  This would require more, not less, government “for energy production, for fuel efficiency, for reforestation,” she concluded. 
Thatcher went on to found the Hadley Center for Climate Prediction and Research and gave early direction to the Intergovernmental Panel on Climate Change (IPCC) to elevate the issue at home and abroad.  She held a press conference upon the release of the first IPCC assessment (1990) and warned that “greenhouse gases … will warm the Earth’s surface with serious consequences for us all.” 
Thatcher, who left office in 1990, lobbied George H. W. Bush to sign the United Nations Framework Convention of Climate Change (1992), the parent document of future climate treatises. As much as she might have regretted it, the process she set into motion resulted in the ill-fated Kyoto Protocol of December 1997. 
In her retrospective, The Downing Street Years (1993), Thatcher, while wary of “green socialism,” described how her environmental concern expanded from stratospheric ozone to “another atmospheric threat,” man-made global warming. 
What was behind Thatcher’s “conversion experience” to climate alarmism in 1988? Part of the answer was the pressure she received from her advisors John Houghton and Sir Crispin Tickell, who were in step with the emerging environmental movement. Also, global warming was an issue that provided her with enhanced international prestige.
But perhaps most important was her vigorous battle against the nationalized, unionized coal-mining sector, the leadership of which was socialistic at heart and determined to break her reform agenda.
The memories of Arthur Scargill of the National Union of Mineworkers using thuggery against strike breakers in the long months of 1984–85, and her preference for nuclear power to generate electricity, undoubtedly made her welcome an environmental issue that would help cut coal down to size.
Natural gas from the North Sea, too, was poised to replace coal and significantly reduce CO2 emission rates in electricity generation. It would have been undoubtedly different for the Prime Minister had carbon-emission reductions not been an affordable option for the U.K. 
Mugged by Reality: Nonalarmism
In Statecraft: Strategies for a Changing World (2002), Thatcher declared war on “the doomsters’ favorite subject … climate change.”
Here is her full reconsideration (pp. 449–50):
The doomsters’ favorite subject today is climate change. This has a number of attractions for them. First, the science is extremely obscure so they cannot easily be proved wrong. Second, we all have ideas about the weather: traditionally, the English on first acquaintance talk of little else.
Third, since clearly no plan to alter climate could be considered on anything but a global scale, it provides a marvelous excuse for worldwide, supra-national socialism. All this suggests a degree of calculation. Yet perhaps that is to miss half the point. Rather, as it was said of Hamlet that there was method in his madness, so one feels that in the case of some of the gloomier alarmists there is a large amount of madness in their method.
Indeed, the lack of any sense of proportion is what characterizes many pronouncements on the matter by otherwise sensible people. Thus President Clinton on a visit to China, which poses a serious strategic challenge to the US, confided to his host, President Jiang Zemin, that his greatest concern was the prospect that “your people may get rich like our people, and instead of riding bicycles, they will drive automobiles, and the increase in greenhouse gases will make the planet more dangerous for all.”
It would, though, be difficult to beat for apocalyptic hyperbole former Vice President Gore. Mr Gore believes: ‘The cleavage in the modern world between mind and body, man and nature, has created a new kind of addiction: I believe that our civilisation is, in effect, addicted to the consumption of the earth itself.’
And he warns: “Unless we find a way to dramatically change our civilisation and our way of thinking about the relationship between humankind and the earth, our children will inherit a wasteland.”
But why pick on the Americans? Britain’s then Foreign Secretary, Robin Cook, has observed: “There is no greater national duty than the defense of our shoreline. But the most immediate threat to it today is the encroaching sea.” Britain has found, it seems, a worthy successor to King Canute.
The fact that seasoned politicians can say such ridiculous things – and get away with it – illustrates the degree to which the new dogma about climate change has swept through the left-of-centre governing classes….
What had changed for Thatcher in less than a decade? First, she found climate science less alarming than before. Secondly, an “ugly … anti-growth, anti-capitalistic, anti-American” political agenda had emerged around the issue.  Harking back to her free-market roots, Thatcher forwarded her own version of the precautionary principle: “Government interventions are problematic, so intervene only when the case is fully proven.” 
Thatcher’s about-face can be chalked up to experience and regret about helping to create what became the anti-capitalist Kyoto Protocol (1997). Another explanation is that Thatcher’s bitter battle against the nationalized, unionized coal mining industry, which to her “symbolize[d] everything that was wrong with Britain,” was over. 
The leadership of Prime Minister Margaret Thatcher in the United Kingdom from 1979 until 1990 “recast attitudes toward state and market, withdrew government from business, and dimmed the confidence in government knowledge.” 
Thatcher praised the free and open economy as a worthy ideal in stark contrast to Britain’s tradition of democratic socialism. One of her greatest tests was the British coal strike of 1984–85, which was broken after a year. Electricity generation and distribution were privatized in 1990, and the coal industry, which had been nationalized back in 1946, soon followed in the new light of the free market.
But in the process, Margaret Thatcher jumped too quickly on the climate issue for short-run gain. The good news is that she quickly and completely corrected herself. She got “mugged by reality,” as they say.
And so she is today a disappointment to red-green environmentalists, who preferred socialism to her privatizations.  “[H]er enthusiasm for green issues soon evaporated,” stated John Vidal. ”In retirement she had nothing more to say about the environment until her 2002 memoirs, when she rejected Al Gore and what she called his ‘doomist’ predictions.”
So be it for her legacy and for posterity.
 Thatcher, Margaret. The Downing Street Years. New York: HarperCollins, 1993, p. 640.
 Ibid., p. 640.
 Ibid., p. 641.
 Bradley, Capitalism at Work: Business, Government, and Energy. Salem, MA: M & M Scrivener Press, 2008, p. 286.
 Quoted in Jeremy Leggett. The Carbon War: Global Warming at the End of the Oil Era. London: Penguin, 1999, p. 4.
 Bradley, Capitalism at Work, p. 286.
 Thatcher, The Downing Street Years, pp. 639, 640.
 Bradley, Capitalism at Work, p. 287–88.
 Thatcher, Margaret. Statecraft: Strategies for a Changing World. New York: HarperCollins, 2002, pp. 452–53.
 Ibid., p. 453.
 Thatcher, The Downing Street Years, p. 340.
 Yergin, Daniel, and Stanislaw, Joseph. The Commanding Heights. New York: Simon & Schuster, 1998, pp. 122–23.
 Complained Vidal: “The free market economics that her governments espoused dramatically changed the green face of Britain. In a series of controversial privatisations, her ministers encouraged urban sprawl by approving massive out-of-town supermarket developments, deregulated or privatised the bus services, spent billions of pounds on new roads but little on rail transport, and handed ownership of water and waste to global corporations. She balked only at the railways, saying it was “a privatisation too far.”