A recent research study provides the clearest insight into the variations of Earth’s surface temperature over the past 485 million years. The findings indicate that Earth has experienced and is capable of reaching temperatures higher than those of today, yet both humans and wildlife cannot adapt swiftly enough to cope with the rapid climate changes induced by human activity.
This study, published in the journal Science, showcases a curve that tracks global mean surface temperatures, demonstrating that Earth’s temperature fluctuations were more significant than previously recognized during the Phanerozoic Eon, a lengthy geological period marked by the evolution of diverse life forms, colonization of land, and several mass extinction events. The curve also reaffirms the strong link between Earth’s temperature and atmospheric carbon dioxide levels.
The Phanerozoic Eon kicked off 540 million years ago with the Cambrian Explosion, a time characterized by the emergence of complex, shelled organisms in the fossil record. Although experts can simulate climate conditions from 540 million years ago, the temperature curve in this study centers on the last 485 million years due to the lack of geological temperature data from earlier periods.
“Finding ancient rocks that also retain temperature indicators is quite challenging — even for 485 million years ago, examples are scarce. This limited our historical scope,” explained Jessica Tierney, a paleoclimatologist at the University of Arizona and co-author of the study.
The research team developed the temperature curve using a methodology called data assimilation, allowing them to merge geological data with climate model outputs for a more comprehensive view of past climates.
“This technique was initially crafted for weather forecasting,” stated Emily Judd, the lead author of the study and a former postdoctoral researcher at the Smithsonian National Museum of Natural History as well as the University of Arizona. “Instead of predicting future weather patterns, we applied it to reconstruct historical climates.”
Enhanced insights into Earth’s temperature changes throughout history are vital for understanding current shifts in climate.
“If we only analyze the past million years, we won’t encounter conditions resembling what we might see in 2100 or 2500,” commented Scott Wing, a co-author and curator of paleobotany at the Smithsonian. “We need to look further back to when Earth was significantly warmer, as this will help us better predict future climate tendencies.”
The new temperature curve reveals that fluctuations have been greater over the last 485 million years than earlier thought. Global temperatures varied between 52 and 97 degrees Fahrenheit, with extreme heat periods correlating with high atmospheric carbon dioxide levels.
“This study clearly shows that carbon dioxide has been the primary influence on global temperatures throughout geological history,” remarked Tierney. “Colder temperatures correspond to low CO2 levels, while warmer temperatures relate to high CO2 levels.”
The research also indicates that the current global temperature of 59 degrees Fahrenheit is cooler than many historical periods in the Phanerozoic. However, human-caused emissions are heating the planet at a rate surpassing even the most rapid warming incidents of the Phanerozoic, significantly threatening global species and ecosystems, and causing swift sea level rise. Some periods of fast climate changes in the past resulted in mass extinctions.
Rapid movement toward a warmer environment poses significant threats to humanity, which has predominantly lived within a narrow temperature range of 10 degrees Fahrenheit, in contrast to the expansive 45-degree variation observed over the last 485 million years, according to the researchers.
“Our species evolved in a climate that could be characterized as an ‘ice house,’ which does not reflect the majority of Earth’s geological history,” Tierney noted. “We are altering the climate into a situation that is quite unfamiliar to humans. The planet has been, and can be, warmer — but humans and animals are unable to adapt quickly enough.”
The collaboration between Tierney and researchers at the Smithsonian began in 2018 with the aim of providing museum-goers with a visual representation of Earth’s global temperature variations throughout the Phanerozoic era, from around 540 million years ago to the present.
The research team gathered over 150,000 ancient temperature estimates derived from five different chemical markers preserved in fossilized shells and other organic materials. Their counterparts at the University of Bristol ran more than 850 simulated climate models representing various historical periods based on the positions of continents and atmospheric composition. The team merged these two types of evidence to form the most precise depiction of how Earth’s temperature has fluctuated over the past 485 million years.
Another key takeaway from the study involves climate sensitivity, which measures how much the climate warms in response to a doubling of carbon dioxide levels.
“We discovered that carbon dioxide levels and temperature are closely intertwined, consistently across the past 485 million years. There’s no indication that the climate is more responsive to CO2 changes depending on whether it’s hot or cold,” explained Tierney.
Beside Judd, Tierney, Huber, and Wing, the study also includes co-authors Daniel Lunt and Paul Valdes from the University of Bristol, as well as Isabel Montañez from the University of California, Davis.
The research was funded by Roland and Debra Sauermann via the Smithsonian, the Heising-Simons Foundation, and the University of Arizona’s Thomas R. Brown Distinguished Chair in Integrative Science, alongside the UK’s Natural Environment Research Council.
