July set to be world's warmest month on record

So hot has the month been to date that researchers are confident the 2019 record will be broken, even with several days to go. UN chief Antonio Guterres said the planet is entering an "era of global boiling".  Scientists agree the extra heat is mainly linked to fossil fuel use.

US President Joe Biden described climate change as an "existential threat" and that no one "can deny the impact of climate change anymore". Some experts believe that July might well be the warmest month in the past 120,000 years. 

Researchers are not surprised that July is set to break the current record for the warmest month as there have been plenty of indications in recent weeks that the world is seeing far greater levels of heating.  The world's warmest day occurred on July 6, and the hottest 23 days ever recorded were all this month, according to the Copernicus Climate Change Service.

Their provisional average temperature for the first 25 days of the month is 16.95C, which is well above the 16.63C figure for the whole of July 2019. 

Other analysis has come to the same conclusion.

Dr Karsten Haustein from the University of Leipzig has calculated that July 2023 will be 1.3C-1.7C above the average July temperatures recorded before the widespread use of fossil fuels. The best guess is around 1.5C. He's confident that even if the last few days are cooler, the margin of error is enough to make July the hottest yet seen.

"Not only will it be the warmest July, but the warmest month ever in terms of absolute global mean temperature," he said in a statement. 

"We may have to go back thousands if not tens of thousands of years to find similarly warm conditions on our planet."

Researchers work out the global air temperature by taking readings from weather stations dotted around the world. 

However there are not enough stations to give a completely accurate global picture so scientists feed all of these readings - plus some measurements from the atmosphere itself - into computer models. 

These allow scientists to create a "map without gaps", meaning the global temperature can be reliably estimated.

By combining these datasets with global weather forecasts for the next few days, scientists can come up with a reliable estimate of the global temperature even before the end of the month.

While July is likely to be the warmest in records dating back around 150 years or so, some researchers believe the final temperature may be the warmest in tens of thousands of years. 

To work out these ancient figures, scientists use records like the air trapped in polar ice cores, or sediments in the deep ocean. These capture a signal of the climate at the time.

From this evidence, while scientists can't pinpoint specific months going that far back, they say the last time the world was similarly warm was about 120,000 years ago - when sea levels were around 8m higher than today, and hippos were present as far north as Britain.