A climate extravaganza got underway in Glasgow, Scotland, on Sunday. President Biden showed up. So have other world leaders and a small city's worth of diplomats, business executives and activists. It's billed as a potential turning point in the struggle to avert the worst effects of climate change, and it has a curious name: COP26.

Is it worth the hype? What might it accomplish? Here's what you need to know.

Q. What's a COP?

These climate meetings began in 1992, when countries signed a treaty promising to stabilize greenhouse gas concentrations in the atmosphere and prevent dangerous changes to the climate. Almost every year since then, the parties to this agreement have met to talk about what still needs to be done. It's called a Conference of Parties, or COP. This is the 26th such meeting. So, COP26.

Q. Who is showing up?

An astonishing collection of people. Saleemul Huq, from the International Centre for Climate Change and Development in Bangladesh, has been to every single COP. He calls the meeting, which will last for two weeks, a "multi-ring circus." In the innermost ring, blue-badged diplomats from almost 200 countries will debate the wording of a statement that's released at the meeting's conclusion, which contains any actual decisions. Other venues in Glasgow will be flooded by celebrities, industry groups, climate activists and academic researchers, all with their own priorities. Protests are expected. It looks to be like a session of Congress, a trade show and a political demonstration all rolled into one.

Q. What is COP26 supposed to accomplish?

There's one main goal: get closer to fulfilling promises that nations made six years ago at COP21 in Paris. Under the Paris Agreement, countries pledged to collectively cut their greenhouse emissions enough to keep the planet from heating up more than 1.5 degrees C (2.7 degrees Fahrenheit), compared with pre-industrial times. Wealthy countries also promised large amounts of aid to poorer nations to help them cope with climate change and to reduce their own greenhouse emissions.

Progress toward those goals has been halting, at best. But pressure is growing for bolder action, because scientists say that planetary warming is accelerating , leading to more frequent and intense heat waves and storms and destruction of ecosystems. The planet already has warmed by about one degree Celsius. Keeping warming below 1.5 degrees C will require quick, drastic cuts in global greenhouse emissions, bringing them practically to zero within about 30 years.

"I'm optimistic, not in a naive sense, because the conditions for this are extraordinarily difficult," says Christiana Figueres, formerly the United Nations' climate chief. "This is incredibly difficult. [But] do we need a success out of this? Absolutely. We don't have the option or the luxury of failure."

Q. Will diplomats sit around a table and negotiate limits on their countries' greenhouse emissions?

Not exactly. The Paris Agreement created a novel method for getting to this goal. It works like a GoFundMe, except for the planet. Countries offer their individual "contributions" — their specific plans to cut heat-trapping emissions. The U.N. then adds them all up and calculates if that sum is enough — or, as now, if a gap remains between those plans and what climate scientists say is needed to avoid the most catastrophic effects.

The Glasgow meeting is forcing countries to declare their plans to cut emissions, and maybe go bigger. "This is arguably the most important COP since 2015" when the Paris Agreement was signed, Figueres says. "We're going to [go] around the table, we're going to be transparent with each other. We're going to say what we did. And above all, what more we are going to do."

Rachel Kyte, dean of the Fletcher School of Law and Diplomacy at Tufts University, says private companies and philanthropists feel the same pressure. "Having the event has an effect," says Kyte, who is also advising the United Kingdom on aspects of the climate talks. "There is huge pressure from civil society, from the public, from investors, from politicians, to go to Glasgow with something [to offer.] People want to be seen to be doing the right thing."

Q. How is this global GoFundMe going so far?

Poorly. Greenhouse gases continue to pour into the atmosphere at a high rate. Even the plans that countries have submitted since Paris would allow global emissions to continue increasing. According to the nonprofit Climate Action Tracker, major polluting countries have submitted plans that are either "critically insufficient" or "highly insufficient." They include Russia, China, Brazil, India and Australia.

The U.S. recently improved its rating to merely "insufficient." Earlier this year, it promised to cut its greenhouse gas emissions in half (compared with 2005 levels) by 2030 and to deliver $10 billion a year in climate-focused economic aid to lower-income countries. But those are just promises right now. Congress hasn't passed legislation that would accomplish this so far, although the Biden administration has offered a new plan that calls for large investments in climate initiatives.

Nations also have not delivered on their promises regarding "climate finance" — the stream of money that will help poorer countries deal with the consequences of a warming climate. Developing nations emit small quantities of heat-trapping pollution but suffer disproportionately from its effects and have fewer resources available to cope with it.

"We're not on track. It's not happening. Why isn't it happening? That's the story," says Saleemul Huq.

There is some mildly good news, though. According to the latest estimate from the International Energy Agency, if all countries fully carry out their current climate pledges, the global curve of greenhouse emissions eventually will start to bend downward. Under this scenario, average global temperatures would increase by 3.7 degrees Fahrenheit compared with pre-industrial levels by the end of the century. (Those average temperatures have already risen by about two degrees Fahrenheit.) "We are making progress," Figueres says. "We're not at the level that we should be, but we're moving in the right direction."

Q. After all the countries put their plans on the table, what remains to be decided?

Negotiators will argue over the wording of the meeting's final statement. Climate experts are hoping that it will "send a signal" that nations understand the need for deeper emissions cuts to reach that elusive target of limiting warming to 1.5 degrees Celsius.

Poorer countries, many from Africa, will push hard for specific commitments on financial aid to help them deal with climate-linked disasters. "Poor countries are not responsible for this problem," says Chukwumerije Okereke, director of the Centre for Climate Change and Development in Nigeria. "It's been shipped to them by developed countries, and they're having to deal with it with little or no help."

These countries say that previous commitments for $100 billion a year in "climate finance" — even though still unmet — are woefully inadequate.

In addition, negotiators will be trying to work out final details of what's called "The Paris Rulebook." These include rules for how countries shall report their emissions targets and how a system of "carbon markets" might work, in which one country can effectively purchase emissions reductions from another country.

Rachel Kyte says that one thing is already clear. There will be plenty of work still to do when COP26 is over. "People think that the COP is sort of like the World Series, right? And that there's going to be some, you know, walk-off home run from China or the U.S. And it's not," she says. "It's like an Iditarod, right? Lots of huskies, long and arduous, and maybe it never ends."