What would make COP26 a success?

At COP26 the world’s leaders have left the stage.

The weekend interval has come and gone with just a week to go until the final curtain comes down. That leaves the negotiators they’ve left behind facing a frantic second act.

Already their plenary sessions are running into the small hours, full of raised objections, dense technical detail and back-pedaling.

The aim of this summit sounds simple: to keep 1.5 degrees alive. By that the UK presidency means it wants to gather enough promises to limit global temperature rises to no more than one and a half degrees above pre-industrial levels. 

Last week saw some big pledges. India unexpectedly committed to becoming net zero by 2070, decades later than other major economies, but still real progress. 

There were deals on cutting methane emissions, ending deforestation and moving away from coal. But words aren’t the same as action and on Friday’s youth day of action, the activist Greta Thunberg was scathing. 

"It is not a secret that COP26 is a failure” she told thousands of climate activists.

"It should be obvious that we cannot solve the crisis with the same methods that got us into it in the first place.”

So what would it take for COP26 to be considered a success by environmental scientists and activists alike? 

After crunching through the promises made in the first week by nations, financiers and corporations alike, the Independent Energy Agency believes they are enough to hold the rise in global temperatures to 1.8 degrees by the end of the century. 

That is a landmark moment as it the first time that governments have offered up targets ambitious enough to hold global warming to below 2 °C. 

But (and it’s an absolutely giant but) those promises would have to be met in full and on time, as would all those pledges made previously.  

That’s hard to imagine, given that developing nations are furious that the world’s richer countries have already broken a vow, made at COP21 six years ago, to give them £100 billion a year to help fight climate change. 

So it’s critical that the summit addresses the credibility gap. Negotiators need to find ways to hold countries to account on delivery, possibly by bringing them back to the table as early as 2023. 

Making a final assessment of just how much has been achieved in Glasgow won’t be easy.

Unlike some of the big summits before it, COP26 won't conclude with a new treaty or an obvious big win. 

With a week to go it seems highly unlikely that the UK presidency will be able to gather enough pledges to put the world firmly on course for 1.5C.

Even before the thorny issue of actually getting those pledges delivered is addressed.

The gap is frightening. Scientists believe capping warming at 1.5C would need the world’s emissions to fall by a whopping 45% by 2030 from 2010 levels, and reach net zero by 2050.

At the moment they’re on course to rise by 16% over the next decade. But this summit isn’t an end point. 

The planet and our increasingly extreme weather will offer regular reminders to those involved that time is of the essence. 

If enough credible deals are made, involving enough of the major players here, ambition will grow.

That would be, if not success, then something like it. Maybe we could call it hope.