Rightly, the world has been celebrating the 30th anniversary of the fall of the Berlin Wall. On November 9th 1989 the communist government of East Germany announced that its security forces would no longer prevent people from visiting West Berlin. Quickly, delirious Berliners surged through the old checkpoints or clambered over the wall. Soon the hammers and pick-axes were out, precipitating the dissolution of the Soviet Union.

For the two leaders of the West during the 1980s, Margaret Thatcher and Ronald Reagan, the breaching of the wall was a vindication of years of ideological struggle against the “evil empire”. Reagan had already retired, succeeded as president by George Bush, but Thatcher was in New York, where the previous day, November 8th, she had addressed the United Nations.

The Iron Lady was no fan of the UN; she hadn’t spoken there for four years. But now she had an issue to address that had “grown clearer than any other in both urgency and importance”, and she needed the whole world to listen. Not the end of communism, or even history itself, as was the fashion, but “the threat to our global environment”.

Thatcher thus became the first prominent political leader to warn the world about the danger of climate change, and to outline a strategy to deal with it. The timing of her speech, as communism was crumbling, was no coincidence: she cast climate change as the successor menace to socialism and nuclear annihilation. What she characterised as these “conventional political dangers” appeared to be receding, but now, instead, lay the “prospect of irretrievable damage to the atmosphere, to the oceans, to the earth itself.”

Thatcher’s UN speech was not just a one-off either, but the final part of a trilogy that had begun just over a year earlier at the Royal Society in London. Proud of her membership of Britain’s most prestigious scientific body, and of being one of very few world leaders ever to have studied and trained as a scientist (she worked as a research chemist), the prime minister had enthusiastically accepted an invitation to speak at the society’s annual dinner at Fishmongers’ Hall in the City.

Her advisers cast around for a suitable subject, but it was Thatcher herself who came up with the threat from greenhouse gases and the “large hole” in the ozone layer. The second speech in her trilogy was delivered to the Tory party conference in October 1988, a month after the Royal Society talk. She prided herself on mastering the science of climate change. As Jon Agar, professor of science and technology studies at University College London observes, Thatcher even asked for the exact chemical formulas that were used to analyse acid rain, which she then went through herself.

Thatcher had a galvanising effect on the environmental debate, and in greening mainstream politics. Jonathan Porritt, head of Friends of the Earth in the late 1980s, has argued that she “did more than anyone in the last 60 years to put green issues on the national agenda.” She also put her government’s money where her mouth was. Thatcher ensured that the Treasury invested in the supercomputers to model climate change at the Hadley Centre for Climate Prediction and Research, still one of the world’s leading outfits for such modelling. After she resigned in 1990 she was invited to become a sort of world climate tsar, heading a new institute to spread the word; she was tempted, but eventually turned it down.

Yet whereas Thatcher’s hostility to communism and socialism seemed to be a straightforward battle between good and evil, liberty and oppression, her call to arms on climate change sowed the seeds of an ideological battle that clouds thinking on the subject to this day.

For although she argued for continued economic growth via free enterprise capitalism at the UN, she also suggested that free markets are not an end in themselves, but only a means to an end; contingent upon producing a sustainable environment. “They would defeat their object,'' she continued, “if by their output they did more damage to the quality of life through pollution than the well-being they achieve by the production of goods and services.”

This idea—call it “Green Thatcherism”—was heresy to many of her admirers and ideological bedfellows. All the more so as she further argued that a threat as dangerous as climate change could only be dealt with through multilateral institutions and new international conventions. For this seemed to invite exactly the kind of bureaucratic regulations, official meddling and collectivist thinking that her supporters had spent a lifetime overcoming with the fall of the Berlin Wall. It appeared to be “Socialism through the back door,'' as she herself characterised her objections to an increasingly ambitious European Union in 1988.

Thus her legacy on this issue, unfortunately, remains extremely confused. A few have been inspired by her greenery, and taken her advice to use markets and free enterprise to search for solutions. Many on the left, however, have ignored her perfectly sensible suggestions because they cannot acknowledge that such a hate-figure for people on the left could have contributed anything to the green debate.

This is the wishful thinking of the left. Yet many of her former colleagues and admirers are equally guilty, challenging or denying the science in order to resist the extra regulations and taxes that are required to reduce global warming. This inverts her original argument. Reared on decades of fighting for individual liberty and capitalism against dictatorships and collectivism since the 1930s, their politics moulded by the spectre of Auschwitz and the gulags, such ideological defensiveness is perhaps understandable. Thatcher was reared on exactly the same stuff. But her fellow travellers on the right resist the ideological sacrifices that Thatcher suggested may be necessary for such a threat as global warming.

Thus, for instance, rather than regard climate change as the successor menace to communism, as Thatcher originally did, her erstwhile chancellor, Nigel Lawson, has argued consistently that the “quasi-religion” of “green alarmism”, as he calls it, has replaced the needs for “transcendent values” that communism once provided, leading to all the same evils. Thus this prominent climate sceptic will refight the old battles, dismissing the science to do so.

And much as Eurosceptics have expended a lot of energy poring over a few speeches of Winston Churchill to claim him for their cause, so Thatcherites have parsed her words to try to show that she was never that green in the first place, eager to prove that her Green Period was merely a blemish on an otherwise spotless record. It helps that Thatcher herself, under different influences, later seemed to endorse the “climate change is socialism” line. But as her latest and most comprehensive biographer, Charles Moore, reminds readers, she really did don the green mantle on the world stage, and, moreover, wore it with “panache and sincerity”.

Mark Littlewood, head of Thatcher’s favourite think-tank, the Institute of Economic Affairs, acknowledges that in prioritising ideology over the science, the free-market right has often been guilty of just wishing away all the bad news about climate change in a manner that Thatcher would never have countenanced. Such wishful thinking, of course, permeates the present Trump administration, which routinely trashes the science in order to escape the regulatory consequences of accepting the science. Hence America’s withdrawal from the Paris climate agreement in the name of sovereignty.

Yet, as Thatcher argues in her speeches, this extremism is unnecessary—the free-market system can offer perfectly good solutions to climate-change adaptation, more so, often, than other ideological systems, providing there are incentives to do so and a political will. Harder for the climate sceptics to accept, perhaps, especially in this age of nationalism, is the potential loss of sovereignty involved in the sort of target-setting and politicking envisaged by Paris and other international climate accords.

It is possible to accuse Thatcher of a dismal lack of consistency on sovereignty; she rebelled against the EU, for instance, over the loss of British sovereignty, but was prepared to cede sovereignty to supranational bodies to mitigate climate change.

Yet it was these very inconsistencies that made her such a successful politician and a visionary leader. She herself later swallowed the flattering illusion that she had always been ideologically consistent, to feed the Iron Lady myth—but it is just that, a myth.

The fact is that if both sides removed their ideological blinkers, as Thatcher, remarkably perhaps, managed to do, then her trilogy of speeches in the late 1980s still offer some of the best and clearest thinking on the subject. Indeed, 30 years on, again, she has largely been vindicated by events.

The left might learn that private enterprise can and indeed does produce many of the technical solutions to climate change. Economic growth continues to lift millions out of poverty; richer countries, such as those in the EU, have also done the most to curb carbon emissions over the past few decades. But the right must also reflect that it is a global problem that will only be solved by global co-operation, just as multilateral Western institutions such as NATO, Five Eyes intelligence sharing and the IMF helped to defeat communism.

This is the essence of “Green Thatcherism”; when the Iron Lady went from seeing red to green—forget the hammer, embrace the sickle. Green Thatcherism is as relevant today as Cold War Warrior Thatcherism was in the 1980s. Perhaps even more so.