The Earth’s temperature has been much cooler in the past than previously thought, meaning it could be moving towards the warmest it’s ever been.
Research at the University used a new method of measurement to understand how warm the Earth’s temperature has been over the Phanerozoic period – from around 540 million years ago to the present day.
Studies previously estimated that the planet’s temperature could have reached up to 20C above pre-industrial levels during some geological periods, and maybe even up to 30C above pre-industrial in earlier times when the first animals evolved.
But research published in the journal Nature Communications, reveals that negative feedback processes (natural stabilising processes like rock weathering) have helped to keep the Earth’s temperature regulated over millions of years, which allowed the biosphere to continue evolving.
The study concludes that the Earth’s past warm periods were more likely to have had past temperatures of around 10C above pre-industrial temperatures – hotter than today but much cooler than previously thought.
How far can we push the planet?
Researchers believe these findings could be crucial for understanding the impact of future climate change, as well as exploring biological evolution and extinction, where understanding the heat tolerances of ancient biospheres can help us conserve the present biosphere.
Lead author of the study, Dr Dongyu Zheng from Chengdu University of Technology, conducted the work as a visiting fellow at Leeds. He said: “This study shows how ancient rocks and modern climate simulations can work together to reveal the boundaries of Earth’s long-term climate.
“The evolution and flourishing of life were not sporadic accidents, but were closely linked to Earth’s ability to regulate its climate over geological time.”
Previous studies had used oxygen isotopes in sediments which showed a long-term shift towards lower isotope values, indicating that tropical oceans in the past may have been extremely warm.
Reconstructing past temperatures
Dr Zheng and colleagues instead used the Chemical Index of Alteration (CIA), which measures the depletion in weatherable elements in rock samples and can reveal how sediments have been exposed to warm temperatures in the past. Data used to calculate CIA is widely recorded, resulting in a database of tens of thousands of readings. Using these readings, the researchers were able to reconstruct past global temperatures by combining individual measurements with climate model simulated temperatures in these regions.
Their research also revealed that Earth’s long term climate sensitivity (a measurement of how the Earth’s temperature reacts to increases of carbon dioxide) may be lower than has recently been proposed.
The senior author of the study, Professor Benjamin Mills, Professor of Earth System Evolution at Leeds, said: “The findings suggest that that Earth’s temperature has been tightly regulated over time, and that human-driven warming of 10C – which is possible if all fossil fuel reserved are burned – would take us to places the Earth may never have been before. How far can we push the planet?
“We shouldn’t be complacent when viewing ancient hot climates that supported diverse ecosystems, and we must understand that they were established extremely slowly, and may not have been as hot as recently proposed. Earth’s natural regulation systems are slow, and humans must perform our own climate regulation to keep the planet in a habitable range.”
Further information
The paper, Tight regulation of Earth’s long-term temperature over Phanerozoic time, is published in the journal Nature Communications 9 July 2026.
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