To predict the future, it can help to look at the past.
That's especially true when it comes to climate change: Studying what the planet looked like millions of years ago can give insight into what we can expect as warming continues.
In a study published today in the journal Science Advances, scientists simulated the climate of the Eocene, an era 50 million years ago, for the first time. Back then, the world was 25 degrees Fahrenheit warmer than it is today.
The model's results, which align with geological evidence, suggest that when carbon-dioxide levels in the atmosphere increase, additional increases in CO2 then have an even bigger impact on the climate than they would have otherwise. That doesn't bode well for our own climate future.
Simulating the conditions of a world long gone can make climate models — which scientists use to predict of the future of climate change — more accurate.
"We are constantly using these climate models to do future projections. And the future climate, we know, could be very different than the one we are experiencing and observing," Jiang Zhu, the lead author of the study and a postdoc fellow at the University of Michigan, told Insider.
During the Eocene, Zhu said, the atmosphere had more than double the concentration of carbon dioxide that it does today. But until now, models just didn't simulate it correctly.
So Zhu and his coauthors opted to use a model that the International Panel on Climate Change (IPCC) relied on in its 2014 report (the group's most recent assessment).
That model's calculations turned out to match up with what scientists already knew based on geological evidence: that the Earth had warm temperatures globally during the Eocene, with only a small difference in temperatures between the poles and the equator. The epoch began with a temperature rise of 5 to 9 degrees Celsius.
Before the Eocene even started, global sea levels were estimated to be 40 to 100 meters higher than they are currently. Then sea levels rose even more for millions of years due to a lack of ice on the poles. In the Arctic Circle, there were crocodiles, palm trees, and sand tiger sharks.
If we don't curb greenhouse-gas emissions by the end of the century, it's predicted that the concentration of CO2 in Earth's atmosphere could reach 1,000 parts per million; that's the same as the level during the early Eocene.
We are currently at 415 parts per million — the highest level ever in human history.
The Eocene isn't the only era in Earth's history that's important to study to better anticipate future climate change, though. A study published last year suggests that climates like the one during the Pliocene era will become the norm as soon as 2030.
Zhu said his study shows how using a combination of geological data and climate models can provide the clearest image of the past — and the future.
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