World leaders will meet in the UK in early November for the COP26 climate summit in a last-ditch effort to keep global warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) this century.

The yearly summit, convened by the United Nations and delayed last year because of the coronavirus pandemic, is a place for diplomats to negotiate treaties to slow dangerous changes to the climate. In 2015, they signed up to the Paris Agreement — a non-binding target to keep warming well below 2 C above pre-industrial temperatures, and ideally 1.5 C — yet they continue to burn fossil fuels and chop down trees at rates incompatible with that goal.

Now, with the effects of climate change visible in rich countries as well as poor ones, they are meeting for what analysts expect to be the most meaningful conference since that pledge. Climate change has shot up the political agenda amid deadly weather extremes and mass public protest, and leaders of several polluting countries have pledged to decarbonize their economies by the middle of the century.

"Over the last two decades, we've gone from facing the climate challenge to living in a state of climate emergency," said Shikha Bhasin, a senior analyst at the Council on Energy, Environment and Water (CEEW), a think tank in Dehli. "And that's exactly why the upcoming COP26 is critical."

What's on the agenda?

Under the Paris Agreement, world leaders get to choose how fast their country will cut emissions. They agreed to update their action plans for doing so every five years.

But just weeks before the COP26 summit in Glasgow, big emitters like China, India and Saudi Arabia have failed to submit new plans. A September report by UN Climate Change, the body that organizes international climate negotiations, found that updated plans account for only about half of global greenhouse gas emissions.

The UK, which is co-hosting the summit with Italy, has pressured countries to submit new plans and is pushing for concrete deals that would help reach those targets. Prime Minister Boris Johnson has called on world leaders to deliver bold commitments on "coal, cars, cash and trees."

The UK is pushing for a treaty that would "consign coal to history" and has proposed a deadline of 2040 to stop selling combustion engine cars. It also wants to put more money into stopping deforestation.

Who will pay?

A question at the top of the agenda will be how much money rich countries, which are most responsible for having polluted the atmosphere, will send to poor ones, which are hit hardest by climate change.

In 2009, the wealthiest nations agreed to send $100 billion a year in climate finance by 2020. But in 2019 they fell short of that goal by some $20 billion after stumping up just $79.6 billion, according to the latest estimates from the OECD. In those 10 years the Earth's average temperature had risen so much to make last decade the hottest on record. 

Analysts have said the failure to pay up is important for two reasons. First, because the money is needed, even if it isn't enough to cover the costs of climate change or a transition to renewable energy.

But it's also a diplomatic issue, said Jennifer Tollman, an expert on climate diplomacy at European climate think tank E3G. "Any international negotiations are built on a foundation of trust. The under-delivery on this $100 billion is obviously making that foundation crumble to a certain extent. "

What else matters?

Countries most vulnerable to climate change have called for greater attention — and funding — to be given to adapting to its effects. 

Beyond that, there are technical details from the Paris Agreement that still need to be ironed out before it properly comes into effect. This includes rules around a global carbon market — the way countries trade emissions across borders and "offset" them by investing in projects that reduce pollution — and also the way countries should formally report cuts to their emissions.

The main talks, which take place over two weeks from October 31 to November 12, will bring together world leaders, scientists, businesses and civil society groups. Delegates from poorer countries have warned that travel restrictions, a lack of vaccines and accommodation costs will make it harder for them to come. That would make it more difficult to hold rich historical polluters to account.

At the last COP, in the Spanish capital, Madrid, in 2019, talks overran by two days as frustrated negotiators struggled to compromise on raising ambitions and failed to reach an agreement on carbon markets.

Climate summits have so far failed to hold countries accountable, but COP26 could be a chance to bridge some trust, said Bhasin from the CEEW. "This is what we have and so we have to find a way of making it work."

Correction, October 18, 2021: A previous version of this article misspelled Shikha Bhasin's name. We apologize for the error.