Temperatures of 75°C will one day wipe out humanity

Scientists are predicting a bout of global warming so great it will wipe out the human race even if greenhouse gas emissions were cut to zero tomorrow.

But this won’t happen for another 250 million years.

Researchers have forecast the first mass extinction since the dinosaurs died out 66 million years ago – with temperatures set to reach as high as 75°C and humidity becoming so great it will be far harder to cool down through sweating.

The hottest day ever recorded was 56.7°C in California’s Death Valley in July 1913, according to the World Meteorological Organization, the body recognised as keeper of world records.

Based on the first-ever supercomputer climate models of the distant future, scientists say their research demonstrates how climate extremes will dramatically intensify as the world’s continents very slowly merge to form one hot, dry and largely uninhabitable supercontinent.

When this happens, the study predicts temperatures that are routinely hitting 40°C to 50°C, quite often climbing up to around 65°C and even 75°C – combined with extreme humidity.

Alexander Farnsworth, one of the researchers at Bristol University, told i: “In some places we have some daily weather extremes that can reach upwards of 65°C to 75°C in our simulations.

“The hotter it gets the more humid it can also get. And humidity really matters. It can mean the difference between being able to sweat to cool down in hot temperatures and not being able to – leading to death.

“This would ultimately seal our fate. Humans – along with many other species – would expire.”

The temperature rise will result from three factors, the scientists claim, two of which relate to the formation of the supercontinent known as Pangea Ultima.

First, the Tectonic processes in the Earth’s crust that are slowly bringing the continents together to create a single supercontinent will lead to more frequent volcanic eruptions, which release huge amounts of carbon dioxide into the atmosphere, warming the planet.

Second, much of the cooling effect of the sea of the sea will be lost. The oceans absorb far more heat than the land, curbing temperature rises in hotter weather in coastal areas and inland. As most of the Earth’s surface moves much further from the ocean in the supercontinent that cooling benefit will be reduced – in a process known as the “continental effect”.

Finally, the sun will become about 2.5 per cent brighter in the next 250 million years, adding more energy to the Earth and further warming the world. This is part of a trend, common among all stars, in which hydrogen is converted into helium at an ever-faster rate, in a process called fusion.

These resulting temperature rises also increase humidity because as atmosphere warms, it can hold more moisture.

“The newly emerged supercontinent would effectively create a triple whammy, comprising the continentality effect, hotter sun and more CO₂ in the atmosphere, of increasing heat for much of the planet,” Dr Farnsworth said.

Although human-induced climate change and global warming is likely to be a growing cause of heat stress and mortality in some regions, research suggests the planet should largely remain habitable until this seismic landmass change in the deep future.

But when the supercontinent forms, findings indicate only somewhere between 8 per cent and 16 per cent of land would be habitable for mammals, scientists have said.

“If we look at humans’ natural ability to survive extreme heat then there are several heat-stress thresholds that can’t be crossed in general. Firstly, exposure to Wet Bulb temperatures, which consider heat and moisture, above 35°C for over six hours would be fatal. This even considers total inactivity, full shade, absence of clothing and unlimited drinking water.

“Likewise, Dry Bulb temperatures (what you measure on a thermometer) above 40°C and low humidity for a sustained period of time is also lethal,” Dr Farnsworth said.

Many other species are unlikely to fare much better than humans and other mammals.

“We only looked at mammals, but it would certainly not be a fun place for other species. The fact that much of the continents become aridified – removing a lot of the vegetation on which mammals and other species survive would make life difficult for most species.

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“And plants, in general, do not like temperatures above 40°C. Plants underpin the food pyramid, so if you start to remove them over vast areas you stress the rest of the species, such as insects, which rely on them and subsequently the higher ‘trophic level’ species that in turn rely on them as a food source.”

He argued that there may be a way round total human extinction with the right technology but says that would be a mammoth and highly complex task with no guarantee of success.

In the most shorter term, Eunice Lo, also of Bristol University, said “it is vitally important not to lose sight of our current climate crisis”.

“While we are predicting an uninhabitable planet in 250 million years, today we are already experiencing extreme heat that is detrimental to human health. This is why it is crucial to reach net-zero emissions as soon as possible,” she said.

An ONS analysis last week found that more than 4,500 deaths were linked to extreme temperatures on the hottest days of 2022’s record-breaking heatwave.

It found there were an estimated 4,507 heat-related deaths over the hottest days in England, the most deaths in a 35-year period between 1988 and 2022.

In the warming study, the scientists applied climate models, simulating temperature, wind, rain and humidity trends for the next supercontinent expected to form in the next 250 million years.

To estimate the future level of CO₂ the team used models of tectonic plate movement, ocean chemistry and biology to map out inputs and outputs of CO₂.

The future CO₂ calculations were led by Professor Benjamin Mills, at the University of Leeds, who said: “We think CO₂ could rise from around 400 parts per million (ppm) today to more than 600 ppm many millions of years in the future. Of course, this assumes that humans will stop burning fossil fuels, otherwise we will see those numbers much, much sooner.”

The study is published in the journal Nature.