When the UK landed the Cop26 presidency two years ago, Boris Johnson sensed a huge opportunity to showcase the UK on the world stage. The conference fit his post-Brexit vision of a “global Britain”, free of the EU and still a player on the world stage.

He believed “Glasgow” would be remembered as a historic gathering, like the previous landmark climate summits in Kyoto and Paris. As recently as the end of September, Johnson told the UN general assembly in New York that the Glasgow summit should be a “turning point”. But then a week ago he began to scale down expectations,admitting success was “touch and go”.

Johnson’s characteristic optimism blinded him to the uphill struggle he still faces. Previous landmark Cops succeeded through strong leadership, top-level political engagement and the hard graft of diplomacy over fine detail. Glasgow can still be a success, but not on the basis of the sort of empty sloganeering that brought us global Britain.

Johnson is by nature a proponent of big promises. Initially, it was said, he had toyed with the idea of going further than Paris by beefing up its 1.5C wording. This would be against the wishes of his Cop26 president, Alok Sharma, the former business secretary, who was said to have expressed frustration at Johnson’s overpromising.

Johnson is also accused of not engaging fully with Cop26 until relatively late in the day – in contrast to Laurent Fabius, the former French prime minister who chaired the Paris conference, and Gordon Brown, the UK prime minister who travelled the world before hosting a successful London summit during the financial crisis. Sharma himself was not Johnson’s choice for the role; he had previously approached David Cameron and William Hague. Johnson’s holiday in Spain last month also came at a critical moment in the run-up to Glasgow and raised eyebrows in Whitehall.

Senior UK officials insist progress had already been made. Only 30% of the world economy had committed to net zero greenhouse gas emissions by the middle of the century, when the UK took over the rotating Cop presidency, a figure that has risen to 80%. However, the countries signed up to the 1.5C limit account for about 65% of global GDP, leaving a big gap to bridge. Crucially, the UN’s assessment of the nationally determined contributions offered by individual nations shows that they still leave global temperatures on track to rise by 2.7C.

Johnson’s critics argue he has been too focused on the 2050 target when he should have put more energy into securing the halving of emissions required by 2030; they are on course to fall by only 7.5%, according to the UN. Some insiders see this as an example of his looking at the big picture rather than mastering the detail.

He has also been stymied by poor relations with other world leaders, something that doesn’t bode well for the negotiations in the coming weeks. Brexit has left a legacy of trust issues. Emmanuel Macron, the French president, has warned that the dispute with the UK over fishing rights is a test of Johnson’s “credibility” on the world stage. In London, this was seen as deliberately timed to embarrass Johnson as he prepared to host Cop26. “He is trying to rain on our parade,” one Tory MP claimed.

And despite the need to win the trust of the poorest countries, the UK’s Cop presidency has been undermined by the government’s controversial decision to trim GBP4bn a year from overseas aid in the middle of a pandemic. “It has fuelled the trust problem,” one Whitehall source told me. Another insider admitted: “It’s a bad advert for global Britain.” Rishi Sunak did not use any of the GBP50bn at his disposal in last week’s budget to reverse the cut before 2024-25.

However, all is not lost for Johnson. His government’s ambitious strategy to achieve net zero emissions by 2050 has passed the credibility test and given him the clout needed to progress-chase at Cop26. In his opening speech this morning, he indulged his flair for the dramatic, warning of a James Bond-like Doomsday Clock set at “one minute to midnight”, and that “aspirations” must now be matched by “action”.

He will point to movement by the rich nations towards their promise to provide $100bn a year to help poor countries cope with climate breakdown, although it will arrive three years late, in 2023. He also expressed hope the summit will agree a landmark deal to halt global deforestation by 2030 and reduce methane emissions by a third by 2030. Not the blockbuster announcements of Paris or Kyoto, but real progress on important details left unfinished by previous summits.

This progress depends on many factors coming together. Without more movement by China, the largest emitter of greenhouse gases, overall momentum will stall. “India is unlikely to jump unless China does,” said one UK official. The outcome in Glasgow might depend on the last-minute efforts of John Kerry, the US climate envoy, to extract concessions from China. When Johnson spoke to President Xi Jinping on Friday, he rebuffed the prime minister’s call for China to bring forward its emissions peak from 2030 to 2025.

Johnson hopes to be able to argue this summit kept the 1.5C target alive, even while admitting much more needs to be done over the next few years to achieve it. This Cop is one where the big announcements of previous conferences need to be backed up by the concrete details and deals needed to achieve them. This is not really Johnson’s style. But, were he to pull it off, it would be a big achievement for climate politics and a signal that Britain is a responsible global player.

One idea being toyed with by the UK government is for world leaders to review progress against targets more frequently, perhaps every year or two years, to ensure more action is taken in the current “decisive decade”.

Cop26 might prove a stepping stone, but the word “Glasgow” is unlikely to be remembered as the triumph for global Britain Johnson hoped for in the heady days of 2019.

• Mujtaba Rahman is the managing director for Europe at Eurasia Group, a political risk research and consulting firm