A man stands in a fountain in Bucharest, Romania, on a hot afternoon, July 25, 2023. AP
Searing heat intensified by global warming has baked parts of Europe, Asia and North America this month, combining with wildfires that have scorched across Canada and parts of southern Europe.
"The era of global warming has ended; the era of global boiling has arrived," UN chief Antonio Guterres told reporters in New York.
With the first three weeks of July already registering global average temperatures above any comparative period, the World Meteorological Organization and Europe's Copernicus Climate Change Service (C3S) said it is "extremely likely" that July 2023 will be the hottest month on records going back to the 1940s.
Carlo Buontempo, Director of C3S, said the temperatures in the period had been "remarkable", with an anomaly so large that scientists are confident the record has been shattered even before the month ends.
Beyond these official records, he said proxy data for the climate going back further -- like tree rings, or ice cores -- suggests the temperatures seen in the period could be "unprecedented in our history in the last few thousand years".
Possibly even longer "on the order of 100,000 years" he said.
About 1.2 degrees Celsius of global warming since the late 1800s, driven by the burning of fossil fuels, has made heatwaves hotter, longer and more frequent, as well as intensifying other weather extremes like storms and floods.
The WMO has said the eight years to 2022 were the warmest on record, despite the cooling effects of the La Nina weather pattern. That has now given way to the warming El Nino, although this is not expected to strengthen until later in the year.
"The extreme weather which has affected many millions of people in July is unfortunately the harsh reality of climate change and a foretaste of the future," said World Meteorological Organization's Secretary-General Petteri Taalas.
The WMO predicts it is more likely than not that global temperatures will temporarily rise 1.5C above the pre-industrial benchmark for at least one of the next five years.
They stress, however, that this would not mark a permanent breach of the 1.5C limit set out in the Paris Agreement, which refers to long-term warming.
Buontempo said there had never been a month where so many days had exceeded 1.5C.
Temperature records have tumbled across the northern hemisphere this month, with many regions sweltering through weeks of unrelenting heat.
With large swathes of the United States baking under a record-breaking heatwave, President Joe Biden held a White House conference with mayors of cities like Phoenix, Arizona -- currently enduring a brutal 27-day streak of days above 43 degrees Celsius (110 degrees Fahrenheit) -- to discuss the impact of the extreme temperatures.
He also announced measures to bolster heat-related safety rules for workers - especially farmers, construction workers and others labouring outdoors.
In Beijing, the government urged the elderly to stay indoors and children to shorten outdoor playtime to reduce exposure to the heat and ground-level ozone pollution.
Across the Mediterranean region, extreme heat has left landscapes tinder dry.
In Greece, hundreds of firefighters are struggling to contain deadly wildfires raging for two weeks in multiple parts of the country.
Copernicus and WMO said global average sea surface temperatures, which have well above those previously registered for the time of year since May, have contributed to the exceptionally warm July.
Buontempo said "a significant swathe" of the central Mediterranean is now close to or above all previous records.
The previous hottest month was July 2019, according to Copernicus, which will publish finalised data in early August.
This week scientists from the World Weather Attribution group found that the heatwaves in parts of Europe and North America would have been almost "impossible" without climate change.
Temperatures in China were made 50 times more likely by global warming, they found.