485 Million years of Earth’s surface temperature. [Science, Sep 20, 2024] The entire history of hominid life occurred only in the cool years of the late Cenozoic, on the lower right of the graph. Click for larger image.
A new study offers the most detailed glimpse yet into how Earth’s surface temperature has changed over the past 485 million years. The data show that Earth has been and can be warmer than today — but humans and animals cannot adapt fast enough to keep up with human-caused climate change.
Published in the journal Science, the study presents a curve of global mean surface temperature that reveals Earth’s temperature has varied more than previously thought over much of the Phanerozoic Eon a period of geologic time when life diversified, populated land and endured multiple mass extinctions. The curve also confirms Earth’s temperature is strongly correlated to the amount of carbon dioxide in the atmosphere.
The start of the Phanerozoic Eon 540 million years ago is marked by the Cambrian Explosion, a point in time when complex, hard-shelled organisms first appeared in the fossil record. Although researchers can create simulations all the way back to 540 million years ago, the temperature curve in the study focuses on the last 485 million years since there is limited geological data of temperature before then.
Refining scientists’ understanding of how Earth’s temperature has fluctuated over time provides crucial context for understanding modern climate change. “If you’re studying the last couple of million years, you won’t find anything that looks like what we expect in 2100 or 2500,” said Scott Wing, a co-author on the paper and a curator of paleobotany at the Smithsonian National Museum of Natural History. “You need to go back even further to periods when the Earth was really warm, because that’s the only way we’re going to get a better understanding of how the climate might change in the future.”
The new curve reveals that temperature varied more greatly during the past 485 million years than previously thought. Over the eon, the average global temperature spanned 11 to 36 degrees Celsius. Periods of extreme heat were most often linked to elevated levels of the greenhouse gas carbon dioxide in the atmosphere.
“This research illustrates clearly that carbon dioxide is the dominant control on global temperatures across geological time,” said co-author Jessica Tierney, a paleoclimatologist at the University of Arizona. “When CO2 is low, the temperature is cold; when CO2 is high, the temperature is warm.”
The findings also reveal that the Earth’s current global temperature of 15°C is cooler than Earth has been over much of the Phanerozoic. But greenhouse gas emissions from human-caused climate change are currently warming the planet at a much faster rate than even the fastest warming events of the Phanerozoic, the researchers say. The speed of warming puts species and ecosystems around the world at risk and is causing a rapid rise in sea level. Some other episodes of rapid climate change during the Phanerozoic have sparked mass extinctions.
Rapidly moving toward a warmer climate could spell danger for humans who have mostly lived in a narrow range of cooler global temperatures. “Our entire species evolved to an ‘ice house’ climate, which doesn’t reflect most of geological history,” Tierney said. “We are changing the climate into a place that is really out of context for humans. The planet has been and can be warmer — but humans and animals can’t adapt that fast.”
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