Ancient rocks reveal Earth’s past warm periods were cooler than thought
Workflow illustrating the assimilation of CIA proxy records with HadCM3L simulations to reconstruct global mean surface temperature (GMST). Credit: Nature Communications (2026). DOI: 10.1038/s41467-026-72672-6 ...
Earth's temperature has been much cooler in the past than previously thought, meaning it could be moving toward the warmest it's ever been.
Research at the University of Leeds used a new method to understand how warm 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 20 degrees Celsius above preindustrial levels during some geological periods, and maybe even up to 30 degrees above preindustrial in earlier times when the first animals evolved.
But research published in the journal Nature Communications reveals that negative feedback processes (natural stabilizing processes like rock weathering) have helped keep Earth's temperature regulated over millions of years, allowing the biosphere to continue evolving.
The study concludes that Earth's past warm periods were more likely to have had temperatures of around 10 degrees Celsius above preindustrial temperatures—hotter than today but much cooler than previously thought.
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.
A different read on ancient heat
Lead author Dr. Dongyu Zheng of 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 toward lower isotope values, indicating that tropical oceans in the past may have been extremely warm.
Zheng and colleagues instead used the Chemical Index of Alteration (CIA), which measures the depletion of 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.
A warning from slower climates
Their research also revealed that Earth's long-term climate sensitivity (a measurement of how Earth's temperature reacts to increases in carbon dioxide) may be lower than has recently been proposed.
Senior author Professor Benjamin Mills, professor of Earth System Evolution at the University of Leeds, said, "The findings suggest that Earth's temperature has been tightly regulated over time, and that human-driven warming of 10 degrees Celsius—which is possible if all fossil fuel reserves are burned—would take us to places 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."
Publication details
Dongyu Zheng et al, Tight regulation of Earth's long-term temperature over Phanerozoic time, Nature Communications (2026). DOI: 10.1038/s41467-026-72672-6
Who's behind this story?
MA in English, copy editor since 2021 with experience in higher education and health content. Dedicated to trustworthy science news. Full profile →
Master's in physics with research experience. Long-time science news enthusiast. Plays key role in Science X's editorial success. Full profile →
Citation: Ancient rocks reveal Earth's past warm periods were cooler than thought (2026, July 9) retrieved 12 July 2026 from https://phys.org/news/2026-07-ancient-reveal-earth-periods-cooler.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.