This year will likely be the second or third warmest ever on record globally, as an "unprecedented streak" of high temperatures persists, UN scientists have warned.

It comes as climate talks between world leaders get under way in Brazil.

Prime Minister Sir Keir Starmer and Prince William addressed other nations in the Amazonian city of Belem, including Brazil's president Luiz Inacio Lula da Silva and officials from Jamaica, which is still reeling from the devastating Hurricane Melissa.

Global average surface temperatures in January to August 2025 were 1.42C above pre-industrial times, before humans started burning fossil fuels at scale, the UN's World Meteorological Organisation has said.

The level is closing in on the target set in the landmark Paris Agreement, struck at COP21 in 2015, which aimed to limit global warming to "well below" 2C and ideally 1.5C.

That means just 10 years later, it is already looking "virtually impossible" to stick to the Paris goal without at least temporarily overshooting it, the WMO said.

Under this heat, the UK experienced its hottest summer on record, two million people in Pakistan were evacuated from deadly floods and parts of the Amazon rainforest are so dry that once rare wildfires now spread easily.

Hilde Heine, president of the coral atoll country of the Marshall Islands in the Pacific, said the "widespread mortality of coral reefs [is] now seemingly inevitable" and the Amazon is "likely not far behind in suffering a similar fate".

WMO chief Celeste Saulo stressed it would be "still entirely possible and essential" to bring temperatures down to the 1.5C goal again.

That 1.5C limit is "not just a figure" but a "lifeline for Pacific communities and climate-vulnerable nations" grappling with rising and warming seas, said Shiva Gounden, head of Pacific at Greenpeace Australia Pacific.

"The legal, moral, and political responsibility for climate action has never been stronger, and the ambition leaders take to Belem will define its success."

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Who's staying away?

The leaders are in town over the course of two days, before the COP30 climate summit begins on Monday.

But only about 60 are due to attend, compared with more than double the number in some previous years.

The heads of the world's three largest drivers of climate change, China, the US and India, are all staying at home.

Although many missing leaders will still send officials to the negotiations, diplomats here in Belem are worried that governments are distracted by cost-of-living woes and boosting defence.

They also fear US President Donald Trump will seek to water down any deals from afar by threatening countries that agree to anything too ambitious.

Leaders 'denying reality'

Mariana Menezes, a Brazilian mother caught up in the devastating floods in Rio Grande do Sul last year, said: "We see world leaders denying reality and making plans to expand fossil fuels.

"These people, who once enjoyed full lives with unforgettable summers and long walks outdoors in their youth, are condemning future generations to lives of pollution and disasters."

The WMO's annual State of the Climate reports found that the past 11 years - from the Paris Agreement year of 2015 to 2025 - have each been in the top 11 warmest on record.

And the past three years have been the three warmest years in the record, stretching back 176 years.

In his speech, Sir Keir admitted that the "consensus is gone" on climate change - that cross-party unity on the science has splintered at home and globally.

He made an economic case for net zero, saying the green transition would create jobs and lower household bills.

But despite attacks on climate policies from the Conservatives and Reform, Britons are still concerned about and believe in climate change, and are still buying in to green technology like electric vehicles and heat pumps, Sky News has found.

(c) Sky News 2025: 2025 set to be among hottest years on record, UN scientists warn