GLASGOW — The first day of climate talks got off to a rocky start.

Critics swiftly played down the hours-old agreement struck by world leaders at the Group of 20 summit in Rome on Sunday as symbolic. The deal fell short, they said, making it harder for the next two weeks of climate talks, led by the United Nations, to yield meaningful results aimed at curbing climate disasters.

And organizers kept a close eye on flooding this weekend that forced people from their homes and disrupted travel in Britain for some of the 20,000 people arriving here in Glasgow, driving home the urgency of these talks.

"The climate is sending you a message," Saleemul Huq, the director of the International Center for Climate Change and Development in Bangladesh, said in a tweet."Welcome" he said, to the era of constant devastation, "from human-induced climate change."

The gathering in Scotland to try to avert even worse consequences of climate change was always going to be a challenge. For one thing, it is taking place during a pandemic.

A daily negative rapid coronavirus test, registered with the government, is required for entry, and delegates could be seen putting cotton swabs up their noses outside the tented U.N. hall. Masks are mandatory in the hallways, and British scientists have said they fear that the summit could become a superspreader event.

On top of that, countries have been known to fall short of reaching their goals at past conferences. The summit's nickname, after all, is COP26, which refers to the 26th "conference of the parties" to the United Nations climate change convention.

That means the U.N. has been trying to help solve climate change for more than a quarter century.

The closest countries came to success was in 2015, when nearly 200 nations agreed in Paris to cut greenhouse gas emissions and set a collective goal of ensuring that the rise in global temperatures remains "well below" 2 degrees Celsius above preindustrial levels.

Despite the promises, scientists say the planet is on a trajectory toward a dangerous 2.7-degree temperature rise by 2100.

Today, countries are being asked to help limit temperature increases to 1.5 degrees. It may seem like a small difference, but that additional heat could mean the disappearance of coral reefs, far lower global crop yields and water scarcity for millions of more people.

And wealthy countries will be asked to keep a promise they made more than a decade ago but never fulfilled: to deliver $100 billion annually by 2020 to poor countries to help them pivot away from fossil fuels and build resilience to climate change.

So here's what to expect: Over the next two days, world leaders, including President Biden, will make speeches promising action.

But the real work begins after they leave, when deputy ministers and diplomats try to iron out the details of an agreement that scientists hope will keep the world on a 1.5-degree trajectory of rising temperatures.

"This is the last decade the world has to avoid the worst impacts of global warming," Gaston Browne, the prime minister of Antigua and Barbuda, plans to say on Monday morning, according to excerpts from his prepared remarks. "I plead that we do not squander this crucial opportunity."