Now or Never: Will Glasgow's COP26 Help Save the World From Disaster?

And, most importantly of all, the world had just successfully agreed to defuse another big threat to the atmosphere, adopting the Montreal Protocol on Substances that Deplete the Ozone layer in September 1987.

That had been a tough negotiation, even after the 1985 discovery of the Antarctic ozone hole, and the final agreement was so delicate that the text could not be translated from English into the other five official UN languages, lest their nuances upset the consensus. But the world then moved fast to strengthen and implement it, and by 1990 it was already clear that it would be the most successful ever environmental treaty.

It had been based on the work of a group of atmospheric scientists, so in 1988 the UN set up the Intergovernmental Panel on Climate Change to produce a similar foundation for a climate treaty. Then, in a barnstorming speech--delivered on the very day in 1990 that Michael Heseltine launched his bid to unseat her--Thatcher persuaded the UN's World Climate Conference to call for a climate convention treaty within two years.

That was achieved, but with even greater difficulty, for opposition to action was already mobilizing, especially in the US, grouped around Dan Quayle, Bush's vice president, and John Sununu, his chief of staff.

Clinton and Gore's inaction

Reilly did manage to get a treaty drafted, with invaluable help from another British right-winger, Michael Howard, then environment secretary. It was signed at the giant 1992 Rio Earth Summit. However, as Bush's cabinet warred, it was unclear until the last minute whether he would join in.

The president arrived with two alternative speeches in his pocket--one, as a member of his cabinet then described it to me, as an "in your face" one, the other endorsing the treaty. Eventually he delivered the latter (as it happens, one of the key sentences in it was mine).

The United Nations Framework Convention on Climate Change (UNFCCC) pledged to "stabilize" emissions of greenhouse gases at levels that would avoid dangerous climate change but contained no specifics. In light of the Montreal Protocol, though, it was believed that they would not be long in coming.

Soon afterwards, in 1992, prospects looked even brighter as Bush and Quayle were succeeded by Bill Clinton and his vice-president Al Gore. The latter was a longstanding champion of action who had published a bestselling, radical environmental tome, Earth in the Balance, shortly before becoming elected. But those hopes were soon dashed: at meeting after meeting, US delegates dragged their feet. "Has Gore," participants joked, "read his book?"

Yet the treaty's first COP (Conference of the Parties), which was held in Berlin in 1995, again involved important progress--largely thanks to Angela Merkel in her first big outing on the international stage. As the recently appointed environment minister of the host country, she stitched together an agreement that governments would meet two years later in Kyoto to agree on a protocol containing specific measures. (When she was elected German chancellor in 2005, the climate change skeptic, George W. Bush, tried to enlist her, as a fellow conservative, in his rejection of the resulting 1997 Kyoto Protocol. Merkel drew herself up to her full 5 foot 4 inches and replied: "Mr President, I am responsible for the Protocol.")

The Kyoto meeting (COP3) often came perilously close to breakdown, with the US--led by Gore--originally insisting that the world should aim not to reduce, but merely stabilize emissions of greenhouse gases.

Two men saved it. One--Raul Estrada Oyuela, the Argentinian chairman of the main negotiating committee--became known as "the miracle worker", for forging consensus when it scarcely seemed possible. The other was John Prescott.

Then Tony Blair's deputy prime minister, he became "the walking and talking man", spending the last days (and nights) of the conference doing one or the other--usually both at once--round the conference centre, as he and his deputy, Michael Meacher, forged a political deal.

Prescott slept one hour in the final 48. So relentless was he that the Japanese hosts vainly asked Blair to get him to relax his pressure.

The protocol was agreed just half an hour before another conference was due to move into the building, and only after a secret telephone summit between Blair, Clinton and the Japanese prime minister, Ryutaro Hashimoto, with the German chancellor, Helmut Kohl, also involved.

It was unambitious: only the 37 Western industrialized countries were obliged to reduce emissions, and then by only 5.2% by 2008-2012. Agreement on how to implement it was put off for three years, until COP6 in the Hague.

That event, as it turned out, was held in November 2000, at the same time as George W. Bush and Gore were contesting the results of the US presidential election. Bill Clinton, finally appreciating what was at stake, told his delegates to deal. Prescott (again with Meacher) got major concessions out of the US and its allies, only to have them rejected by radical green European environment ministers. He went back and got more, but again the Europeans resisted, causing him to walk out flamboyantly.

"It's OK," one Scandinavian minister reassured me, eyeing Prescott's retreating back. "There's going to be a new president. We'll get more from him." Oh yeah? Within months, Bush had rejected the Kyoto Protocol altogether.

The next eight years were a hard slog against American opposition. It even took until 2005 to bring the protocol into force. But then came a breakthrough, and it owed much to plastic ducks.

In December 2005, at Montreal's COP11, the US was, as ever, refusing to consider tightening the protocol's targets. When a final compromise was suggested, US negotiators walked out, insisting: "If it looks like a duck, it's still a duck."

Immediately, the most effective US climate campaigner--Philip Clapp, then head of the National Environmental Trust--went out and bought every plastic duck he could find, and started distributing them. Soon they were everywhere, peeping out of delegates' breast pockets, cascading out of ministers' opened briefcases, even bobbing about in lavatories. Reduced to a laughing stock, the US gave way. An agreement was made to start negotiating new emissions cuts: many delegates shed happy tears.

Less joyful tears flowed down the cheeks of Yvo de Boer, the UNFCCC's normally phlegmatic executive secretary, two years later, when faced with renewed American intransigence at COP13 in Bali.

Unprecedentedly, the US was booed and hissed by delegates of the other 190 nations. In a game-changing speech, Papua New Guinea's delegate, Kevin Conrad, told US delegates: "If you are not going to lead, get out of the way." Embarrassed again, the US backed down. The conference agreed to a "roadmap", putting the world on track for the Copenhagen climate summit (COP15) in December 2009.

How 'Hopenhagen' turned horrid

In half a century of covering UN conferences, I have never known such an important one open with as much optimism as "Hopenhagen", as it was dubbed. True, preliminary negotiations had gone slower than expected and there was no prospect of concluding a formal treaty. However, in the preceding weeks, all the main emitters of carbon dioxide had announced unprecedented measures to control their pollution and differences had so narrowed that an effective political agreement seemed within reach. More than 120 leaders rushed to attend, confident of its lustre rubbing off on them.

They were met with a shambles, poorly run by the Danish prime minister, Lars Lokke Rasmussen. The talks began to fall apart as soon as the second day. A compromise text was undermined by being prematurely leaked. Negotiations were constantly obstructed by procedural moves. China and the US were, fatally, at loggerheads. And tempers were exacerbated by appalling organization, which left participants queuing for hours in freezing weather, unable to get in.

By the closing days, when the leaders arrived to celebrate success, there were still some 100 points of disagreement. They found themselves desperately trying to avert disaster. In another unprecedented development, a group of them--including Merkel, the United States' Barack Obama, Britain's Gordon Brown, Brazil's Luiz Inacio Lula da Silva, France's Nicolas Sarkozy, Mexico's Felipe Calderon, Australia's Kevin Rudd, and the Maldives' Mohamed Nasheed--spent hours in a small, dark room hammering out an agreement line by line: Rasmussen later called it "the strangest political meeting in world history".

The leaders sent Obama rushing across Copenhagen to try to get the Chinese leadership on board. He returned glum-faced, with only partial agreement. Merkel persuaded the others to accept it, as better than nothing.

Yet the dramas had only begun. Many nations, particularly developing ones, revolted when this agreement came before the plenary. Amid extraordinary scenes, one delegate compared it to the Holocaust: another dramatically cut open her arm. Britain's then climate secretary, Ed Miliband, was hurriedly called from his bed, where he had retired after the agreement was reached. Sporting his pajamas under his suit, he led a rescue bid.

Rasmussen was humiliated and left the chair. His replacement managed to gavel through a fragile compromise, merely "noting" a 'Copenhagen accord', before it could break apart.

With the whole international effort in dire peril, the COP circus then moved on to Mexico. In fact, the Copenhagen meeting should--under the UN's system of rotation--have been held in Latin America, but the Danes had persuaded the world that they could handle it better. I confess that I myself was glad at the time that the crucial summit was to be held by supposedly efficient Denmark.

So much for stereotyping! The Mexicans ran a brilliant COP16 in Cancun in 2010, which rescued the negotiations and put them on a new track, confirmed the next year by COP17 in Durban, South Africa. Chris Huhne, then energy secretary before his disgrace, played a central role in both meetings and the course was set for the triumphant Paris summit in 2015.

As they prepared COP21, the French--and the UNFCCC's then executive secretary, Christiana Figueres--seemed to study Copenhagen and do the opposite. Heads of government were invited at the start, to give the talks momentum, rather than at the end. Whereas Copenhagen had sought to set top-down global targets, nations were instead asked to present their own plans for reducing emissions. China and America worked closely together. Even the physical arrangements were excellent.

Despite a few last-minute alarms, the results were better than anyone expected: it was agreed to keep the rise of world temperatures "well below 2degC above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5degC above pre-industrial levels".

The last four COPs have been largely inconsequential, but--just like after the Montreal ozone agreement--the world has moved faster than expected to tackle the issue. Paris aspired, against all expectations, to reach net zero emissions some time in the second half of the century. Now 133 countries have committed to achieving the goal by 2050, with China promising to follow by 2060.

There is virtually universal agreement that temperature rise must be kept to 1.5degC as the maximum, that anything above that is just too dangerous. Meanwhile, clean technologies such as renewable energy and electric cars are being adopted faster than anyone could have dreamt of.

Alas, climate change has been accelerating too. It is now clear that we have two decades at most to keep below the 1.5degC danger mark. And national targets and efforts are still falling well short.

So it's crunch time at COP26, which kicks off in Glasgow next Sunday, 31 October. Will Glasgow rank with Paris or Copenhagen? Will Boris Johnson be humiliated like Rasmussen, or celebrated like the French leadership? Watch, as they say, this space.