COP26: Has Boris Johnson got what it takes to get a deal?

It wasn't really meant to happen.

The snappily titled Conference of the Parties, this mammoth environmental, political and diplomatic shindig, or COP26 as it's known, wasn't destined to be held in the UK.

One insider told me "the whole thing was a mistake". Another said: "It was definitely a quirk".

When prospective host Italy seemed to be humming and hawing over it, the cabinet minister at the time, Claire Perry, spotted an opportunity to grab it for the UK.

Downing Street wasn't necessarily convinced, the Treasury was said to be even less charitable about the prospect, but one insider suggests: "One B. Johnson, then foreign secretary, thought the idea for the UK to host such a big event after Brexit would be marvellous."

Glasgow was chosen because the government wanted the opportunity to "plant Union Jacks and display some of the advantages of the Union" by bringing a massive international event to Scotland.

Given that the conference only ended up in the UK as a twist of fate, will the government end up being delighted it took the chance or regretting the gamble?

Getting nearly 200 different countries to actually agree on anything is, politely, a tricky challenge. The choreography of such an event is dizzying. The etiquette of COP meetings is unusual. Rows are likely. Walkouts are possible.

One insider who has participated in previous COP events recalls a meeting where the attendees spent half an hour arguing over whether to designate the particular session as "informal" or "formal" while the shouts and chants of protestors outside could be heard in the room, threatening to drown them out.

This time, one source told me, there could be as many as 300 delegates in the same room, all entitled to have their say. The idea of trying to reach an agreement with that many people seems mind boggling. Don't be surprised if even the first day is spent in a massive bun fight over agreeing what is on the actual agenda.

COP is designed to be inclusive so that everyone taking part can put forward ideas or issues for discussion. That might feel like the right and proper thing to do, but it doesn't make for rapid or straightforward deal making. And there will be moments where it feels like the summit is all going wrong even if the final conclusions are a triumph.

Having spotted the political opportunity a long time ago, however, the government is obviously massively eager to show that the meetings end in success.

Let's face it, while the awareness of climate change and public concern is much higher than it used to be, public and political understanding of all the complexities is not deep or wide.

One opinion polling source told me "COP is literally not on anyone's radar". But inside government, there is intense focus on what will happen and there are yardsticks by which ministers will measure success.

For the government, the broad aim is covered by the catchphrase to "keep 1.5C alive", that is to get a deal that limits increases in the world's temperature to 1.5 degrees, the threshold scientists want to prevent the most dangerous impacts of climate change.

The hard part for Boris Johnson is that, as you might imagine, it's an awful lot harder than just flicking a switch.

The plan to achieve that aim is made up of three main parts.

First, what does each country plan to do about climate change?

Have they promised to become "net zero" at home by the middle of the century? That is, to take out as much greenhouse gas from the atmosphere as they put in it.

And, thirdly, whether they have committed to net zero, or a date, or not what are their own targets for cutting emissions?

Downing Street is hopeful that more countries will make stronger commitments before the summit gets under way.

If big powerful countries that produce lots of greenhouse gases, like China or India, come forward with measly plans, that creates an obvious first big problem. That's why one official suggests the biggest factor in this whole discussion is "when do China's emissions peak?".

Then there is the question of cold, hard, cash.

For years, rich, developed countries have meant to be helping the most vulnerable protect themselves from the worst effects of climate change, and to make their economies greener.

But guess what, when it comes to shelling out billions, you won't be surprised that the conversations get tricky. The challenge is to work out who is responsible for what and when. In the words of one insider: "The core of COP is a closed shop where people have huge rows about who is going to go first, and who is going to pay."

With the possibility that the high stakes diplomacy falters, Boris Johnson also wants the fortnight in Glasgow to demonstrate real world progress.

You may have heard the prime minister's pledge of "coal, cash, cars and trees", and if you haven't, you'll hear plenty more of it in the next couple of weeks. Stand by for practical announcements on all sorts of actions that should help cut carbon use and reduce the environmental damage from the world's economies, whether that's planting trees, expanding the use of electric vehicles, or just showcasing new technologies.

This might be where a lot of the real action is, with work like that of the former Bank of England governor, Mark Carney, who has been looking at how to rewire financial systems.

And there will be a long list of cameos from the global great and good - whether that's Prince Charles, the Archbishop of Canterbury, the Pope or Arnold Schwarzenegger - all urging world leaders and the public to pay attention, and to try to help.

The prime minister has a chance to crank up the momentum at a G20 meeting in Rome this weekend, encouraging world leaders to increase their own enthusiasm, and maybe their own commitments.

But the cocktail of different factors that will bubble together at COP means a successful fortnight is very far from certain.

Organisers also worry about the logistical challenges of such a massive event.

Keeping hundreds of people, fed, warm and watered matters when you are trying to get them to agree on something, one says. Insiders joke that freezing weather that got delegates shivering at the Copenhagen COP in 2009 was one of the factors that contributed to what was regarded as a miserable outcome.

So COP is a political risk and an opportunity for the government. Those who have worked with the prime minister on the issue say "he has got the religion", another says it "matters enormously" to him that the summit is a political success.

There isn't a question over whether Mr Johnson wants to make progress. There are nagging doubts, however, over whether he really comprehends every aspect of the fiendishly complicated detail. One official told me: "He does care, but he doesn't completely understand all of it."

Another climate activist questioned whether, in the closing moments of the summit, the PM had the right political characteristics to salvage a deal if he hadn't mastered all of the specifics, to untangle the knots that might be holding back agreement.

For months activists and even some in government have suggested privately that Downing Street has focused far less on the upcoming summit than was really required, in contrast to the French government in the run up to the landmark Paris summit in 2015.

Number 10 would counter that claim though, pointing out that Mr Johnson has raised the summit in dozens of foreign calls for more than a year. And his president for COP, Alok Sharma, has certainly burned through the air miles trying to build alliances and prepare the ground for progress to be made.

It is not, however, the case that every minister you speak to about the summit responds with wild enthusiasm (although if it's a success stand by for lots of retrospective wriggling to be part of claiming the credit.).

Some of Mr Johnson's MPs describe the whole thing as "incoherent and elitist", with the government's own green policy at home threatening to "knacker us at the election".

Another Tory source suggests there's a big risk of a "greenlash" from voters when the reality of environmental measures hit, although other government insiders claim Downing Street hopes that a successful COP could go some way to improve the Conservatives standing with younger voters.

Given public awareness overall of the summit that might seem like wishful thinking - remember our pollster who suggested the event had barely been noticed so far?

The Glasgow meeting is far from the be-all-and-end-all for the UK and the rest of the world's environmental ambitions. But it is an important and visible pressure point for presidents and prime ministers to show what they are willing to do on the issue of our times.

And for Boris Johnson, who loves the glad-handing of summitry, the grand nature of big international events, it is a chance, he hopes, to show that the UK can lead.

Climate stripes visualisation courtesy of Prof Ed Hawkins and University of Reading.