The U.N. World Meteorological Organization (WMO) and European Union's Copernicus Climate Change Service also said in a joint statement it was "extremely likely" July 2023 would break the record.

"We don't have to wait for the end of the month to know this. Short of a mini-Ice Age over the next days, July 2023 will shatter records across the board," Guterres said in New York.

"Climate change is here. It is terrifying. And it is just the beginning," he told reporters, adding "the era of global boiling has arrived".

The effects of July's heat have been seen across the world. Thousands of tourists fled wildfires on the Greek island of Rhodes, and many more suffered baking heat across the U.S. Southwest. Temperatures in a northwest China township soared as high as 52.2C (126F), breaking the national record.

While the WMO would not call the record outright, instead waiting until the availability of all finalised data in August, an analysis by Germany's Leipzig University released on Thursday found that July 2023 would clinch the record.

This month’s mean global temperature is projected to be at least 0.2C (0.4F) warmer than July 2019, the former hottest in the 174-year observational record, according to EU data.

The margin of difference between now and July 2019 is “so substantial that we can already say with absolute certainty that it is going to be the warmest July”, Leipzig climate scientist Karsten Haustein said.

July 2023 is estimated to be roughly 1.5 degrees Celsius (2.7 Fahrenheit) above the pre-industrial mean. The WMO has confirmed that the first three weeks of July have been the warmest on record.

Commenting on the pattern, Michael Mann, a climate scientist at the University of Pennsylvania, said it was clear by mid-July that it was going to be a record warm month, and provided an "indicator of a planet that will continue to warm as long as we burn fossil fuels".

Normally, the global mean temperature for July is around 16C (61F), inclusive of the Southern Hemisphere winter. But this July it has surged to around 17C (63F).

What’s more, “we may have to go back thousands if not tens of thousands of years to find similarly warm conditions on our planet”, Haustein said. Early, less fine-tuned climate records — gathered from things like ice cores and tree rings — suggest the Earth has not been this hot in 120,000 years.

Haustein's analysis is based on preliminary temperature data and weather models, including forecast temperatures through the end of this month, but validated by unaffiliated scientists.

"The result is confirmed by several independent datasets combining measurements in the ocean and over land. It is statistically robust," said Piers Forster, a climate scientist at Leeds University in Britain.

HOTHOUSE PLANET

Sweltering temperatures have affected swathes of the planet. While night-time is typically cooler in the desert, Death Valley in the U.S. state of California saw the hottest night ever recorded globally this month.

Canadian wildfires burned at an unprecedented pace. And France, Spain, Germany and Poland sizzled under a major heatwave, with the mercury climbing into the mid-40s on the Italian island of Sicily, part of which is engulfed in flames.

Marine heatwaves have unfolded along coastlines from Florida to Australia, raising concerns about coral reef die-off.

Even one of the coldest places on Earth - Antarctica - is feeling the heat. Sea ice is currently at a record low in the Southern Hemisphere’s winter - the time when ice should soon be reaching its maximum extent.

Meanwhile, record rainfall and floods have deluged South Korea, Japan, India and Pakistan.

"Global mean temperature (itself) doesn't kill anyone," said Friederike Otto, a scientist with the Grantham Institute for Climate Change in London. "But a 'hottest July ever' manifests in extreme weather events around the globe."

The planet is in the early stages of an El Nino event, borne of unusually warm waters in the eastern Pacific. El Nino typically delivers warmer temperatures around the world, doubling down on the warming driven by human-caused climate change, which scientists said this week had played an "absolutely overwhelming" role in July’s extreme heatwaves.

While El Nino’s impacts are expected to peak later this year and into 2024, it “has already started to help boost the temperatures”, Haustein said.

July is traditionally the hottest month of the year, and the EU said it did not project August would surpass the record set this month.

However, scientists expect 2023 or 2024 will end up as the hottest year in the record books, surpassing 2016.

(This story has been refiled to remove the double attribution of Guterres)