Past Warming Event Provides Window into Future Climate Change

Warming that occurred almost 56 million years ago isn't all that different from the human-caused global warming we're experiencing today. And a new study suggests that this past warming event can provide a window into future climate change.

During the Paleocene-Eocene thermal maximum, or PETM, 56 million years ago, temperatures rose by 5 to 8 degrees Celsius (9 to 15 degrees Fahrenheit). It also involved the average annual release of at least 0.9 petagrams (1.98 trillion pounds) of carbon to the atmosphere. While it's promising that Earth and most species managed to survive this episode, it also took millennia for them to recover.

"There is a positive note in that the world persisted, it did not go down in flames, it has a way of self-correcting and righting itself," lead author Gabe Bowen, from the University of Utah, said in a statement. "However, in this event it took almost 200,000 years before things got back to normal."

This holds an important lesson for climate change today. If carbon emissions continue at their current rates, the PETM could be a good indicator of what we will see in the years to come.

To shed some light on the issue, University of Utah researchers analyzed sediment cores drilled from Wyoming's Big Horn Basin, and found evidence of two massive increases of carbon, 55.5 million to 55.3 million years ago. With the first one being bigger than the second, it suggests a triggering mechanism may have been at play.

According to the study, releases during the PETM may have approached levels seen in modern times, which are about 9.5 petagrams (20.9 trillion pounds) per year. Since 1900, human burning of fossil fuels emitted an average of 3 petagrams per year, which is even closer to the rate 55.5 million years ago.

"The Paleocene-Eocene thermal maximum has stood out as a striking, but contested, example of how 21st-century-style atmospheric carbon dioxide buildup can affect climate, environments and ecosystems worldwide," Bowen said.

Bowen and his colleagues are quick to note that comparing climate change some 56 million years ago to the present day is somewhat like comparing apples to oranges. For one, the global climate was already much warmer when the PETM began, and there were no icecaps. Despite these differing factors, this study, published in the journal Nature Geoscience, gives scientists the best idea yet of how climate change will impact our planet in the future.

"This new study tightens the link," Bowen added. "Carbon release back then looked a lot like human fossil-fuel emissions today, so we might learn a lot about the future from changes in climate, plants, and animal communities 55.5 million years ago."

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