The Last Time CO2 Was This High, Humans Didn't Exist

Andrew Freedman

The final fourth dimension at that place was this much carbon dioxide (CO2) in the Earth's atmosphere, mod humans didn't exist. Megatoothed sharks prowled the oceans, the earth's seas were upwardly to 100 feet higher than they are today, and the global average surface temperature was up to 11°F warmer than information technology is now.

As we near the record for the highest CO2 concentration in homo history — 400 parts per 1000000 — climate scientists worry about where nosotros were then, and where we're rapidly headed now.

Co-ordinate to data gathered at the Mauna Loa Observatory in Hawaii, the 400 ppm mark may briefly exist exceeded this month, when CO2 typically hits a seasonal height in the Northern Hemisphere, although information technology is more likely to take a couple more than years until it stays in a higher place that threshold, co-ordinate to Ralph Keeling, a researcher at the Scripps Institute of Oceanography.

CO2 levels are far college now than they accept been for anytime during the by 800,000 years.
Click image to overstate. Credit: Scripps Establishment of Oceanography.

Keeling is the son of Charles David Keeling, who began the CO2 observations at Mauna Loa in 1958 and for whom the iconic "Keeling Curve" is named.

Carbon dioxide is the most important long-lived global warming gas, and one time it is emitted by called-for fossil fuels such as coal and oil, a unmarried CO2 molecule can remain in the atmosphere for hundreds of years. Global CO2 emissions reached a record high of 35.6 billion tonnes in 2012, up two.half-dozen per centum from 2011. Carbon dioxide and other greenhouse gases warm the planet by absorbing the sun's free energy and preventing heat from escaping back into space.

The news that CO2 is nearly 400 ppm for the first time highlights a question that scientists accept been investigating using a variety of methods: when was the last time that CO2 levels were this loftier, and what was the climate like dorsum and then?

There is no unmarried, agreed-upon answer to those questions as studies show a wide date range from betwixt 800,000 to 15 million years ago. The most directly evidence comes from tiny bubbling of ancient air trapped in the vast water ice sheets of Antarctica. Past drilling for ice cores and analyzing the air bubbles, scientists have plant that, at no bespeak during at least the by 800,000 years take atmospheric CO2 levels been equally high as they are now.

That means that in the unabridged history of human civilization, CO2 levels take never been this high.

The Keeling Curve, showing CO2 concentrations increasing to near 400 ppm in 2013.
Credit: NOAA.

Other research, though, shows that you lot have to go back much farther in time, well beyond 800,000 years ago, to find an example where CO2 was sustained at 400 ppm or greater.

For a 2009 study, published in the journal Science, scientists analyzed shells in deep sea sediments to guess past CO2 levels, and plant that CO2 levels have not been as high as they are now for at least the past 10 to fifteen million years, during the Miocene epoch.

"This was a time when global temperatures were substantially warmer than today, and at that place was very piffling water ice effectually anywhere on the planet. And then sea level was considerably college — around 100 feet higher — than it is today," said Pennsylvania Country Academy climate scientist Michael Mann, in an e-mail chat. "It is for this reason that some climate scientists, like James Hansen, take argued that even electric current-day CO2 levels are too high. There is the possibility that we've already breached the threshold of truly unsafe human influence on our climate and planet."

Sea levels are increasing today in response to the warming climate, as ice sheets melt and seas expand due to rising temperatures. Scientists are projecting upwardly to iii feet or more of global sea level rising by 2100, which would put some coastal cities in peril.

While at that place have been past periods in Globe'south history when temperatures were warmer than they are now, the charge per unit of change that is currently taking place is faster than near of the climate shifts that have occurred in the by, and therefore it will likely exist more than difficult to conform to.

A 2011 report in the journal Paleoceanography found that atmospheric CO2 levels may have been comparable to today's as recently equally quondam betwixt 2 and iv.6 million years agone, during the Pliocene epoch, which saw the arrival of Human being habilis , a possible ancestor of modern human sapiens, and when herds of giant, elephant-like Mastadons roamed N America. Modern homo civilization didn't arrive on the scene until the Holocene Epoch, which began 12,000 years ago.

Regardless of which estimate is correct, information technology is articulate that CO2 levels are now higher than they accept ever been in flesh's history. With global CO2 emissions standing on an upward trajectory that is likely to put CO2 concentrations above 450 ppm or higher, it is extremely unlikely that the steadily rising shape of the Keeling Curve is going to alter someday before long.