Only those with new, specific and bold plans can command the podium and the ever-warming world's attention, Secretary-General Antonio Guterres says.

So sit down, Brazil. Sit down, Saudi Arabia. Sit down, Poland.

"People can only speak if they come with positive steps. That is kind of a ticket," Guterres said. "For bad news, don't come."

As if to underscore the seriousness of the problem, the UN's World Meteorological Organisation released a science report on Sunday showing that in the past several years, warming, sea level rise and carbon pollution have all accelerated.

Brazil's, Poland's and Saudi Arabia's proposals for dealing with climate change fell short, so they're not on Monday's summit schedule. The United States didn't even bother, according to a UN official, who spoke on condition of anonymity.

The bar isn't that high: Leaders from 64 nations, the European Union, more than a dozen companies and banks, a few cities and a state will present plans at the secretary-general's Climate Action Summit.

Guterres wants nations to be carbon-neutral by 2050 - in other words, they will not add more heat-trapping greenhouse gases into the air than are removed by plants and perhaps technology each year.

On Sunday, 87 countries around the world pledged to decarbonise in a way consistent with one of the international community's tightest temperature goals.

There is a sense of urgency, Guterres said, because "climate change is the defining issue of our time".

"For the first time, there is a serious conflict between people and nature, between people and the planet," Guterres said.

He wants countries to commit to no new coal power plants after 2020 and reduce carbon pollution by 45 per cent in the next century. The purpose of the summit is to come up with new green proposals a year earlier than the 2020 deadline that is in the 2015 Paris climate agreement.

World leaders agreed in 2009 to try to keep warming to just 2 degrees Celsius since pre-industrial times. Then in 2015, they added a secondary, tougher goal, at the urging of small islands, to keep warming to just 1.5C.

The new weather agency report showed that the world has warmed already by 1.1C. So that means the goals are to limit further warming to 0.9C or even 0.4C from now.

Efforts to reduce carbon pollution need to be tripled to keep from hitting the 2C mark and must increase fivefold to limit warming to 1.5C since pre-industrial times, the World Meteorological Organisation report said.

The weather agency said the past five years were the warmest five on record and even 0.2C hotter than the first half of the decade, a significant jump in just a few years.

"There is a growing recognition that climate impacts are hitting harder and sooner than climate assessments indicated even a decade ago," the 28-page report said.

Australian Associated Press