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7 years in the works, Kohn and international research team uncover CO2 levels of geological past

Matt Kohn, Allison Corona photo.
Matt Kohn

Matt Kohn, a university distinguished professor in the Department of Geosciences, is part of a team of 80 scientists from 16 nations who have studied ancient atmospheric carbon dioxide (CO2) levels and corresponding temperatures to paint a picture of where Earth’s climate may be headed. Their work was published in the journal Science titled “Toward a Cenozoic history of atmospheric CO2.”

“It culminates seven years’ effort from a large international team of scientists – the very best in their specialties in the world – to really nail down our understanding of CO2 levels in the geological past,” Kohn said. “This kind of effort is, in my experience, unprecedented.”

According to a Columbia Climate School press release, their study covers geologic records from the past 66 million years, and it indicates that the last time atmospheric carbon dioxide consistently reached today’s human-driven levels was 14 million years ago. The team found that long-term climate is highly sensitive to the greenhouse gas, with cascading effects that may evolve over many millennia. The report suggests that variations in CO2 affect climate, as well as ecosystems.

“The results are sobering because, in the past, Earth’s temperature was much more sensitive to increases and decreases in CO2 than models predict for today,” Kohn added. “Of course, temperatures in the past evolved over tens of thousands to millions of years. Humans today are forcing climate on a much shorter time scale. But temperatures over the next centuries or millennia might rise much more than we currently think. This doesn’t mean current models are wrong, simply that they may be short-sighted.”

They found that 16 million years ago was the last time CO2 was consistently higher than it is now, and by 14 million years ago it had sunk to today’s human-induced level. About two million years ago, the decline continued and kicked off a series of ice ages. The report goes on to state that “it was at or below that when modern humans came into being about 400,000 years ago, and persisted there until we started messing with the atmosphere on a grand scale about 250 years ago.”

Kohn and this consortium is now an even larger project that charts how CO2 and climate have evolved over the entire Phanerozoic eon, from 540 million years ago to present.