A sudden, unexplained spike in atmospheric carbon dioxide (CO2) during the Cenozoic era approximately 56 million years ago increased global temperatures by five degrees Celsius, resulting in large die-offs of marine life due to ocean acidification.
Known as the Palaocene-Eocene Thermal Maximum (PETM), this event involved the release of 2,500 to 4,500 billion tons of CO2 at a rate of one billion tons per year, heating up the planet for a period of 100,000 years.
Studying this era is crucial because humans today are emitting CO2 at a much greater rate than occurred naturally during the PETM, according to a study led by University of Hawaii professor Richard Zeebe, published in the journal Nature Geoscience.
“If you look over the entire Cenozoic, the last 66 million years, the only event that we know of at the moment, that has a massive carbon release and happens over a relatively short period of time, is the PETM,” Zeebe emphasized.
“We actually have to go back to relatively old periods, because, in the more recent past, we don’t see anything comparable to what humans are currently doing.”
Scientists are uncertain as to what caused the PETM spike in atmospheric CO2 and how quickly that increase occurred.
Theories include a sudden release of underwater methane and or carbon released by melting Arctic permafrost, both of which might have been set in motion by volcanic eruptions.
Zeebe and his fellow researchers studied deep ocean sediments off the coast of New Jersey, searching for carbon and oxygen isotopes that reveal the amount of CO2 in the atmosphere during the PETM as well as its influence on temperatures.
This allows them to determine how much time passed between the carbon’s entrance into the atmosphere and resulting climate changes. A large interval between the two indicates high levels of carbon were released while a small interval or none means less carbon was emitted over a longer time period.
Geologic evidence from the sentiment samples showed no lag time between the release of the carbon and changes in climate, meaning a large amount of carbon was emitted in a short time.
In contrast to the one billion tons of carbon released every year during the PETM, humans are now releasing 10 billion tons per year, meaning resulting climate changes could be more extreme than those during the Cenozoic era.
“If anthropogenic emissions rates have no analog in Earth’s recent history, then unforeseeable future responses of the climate system are possible,” the study said.