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

Andrew Freedman

The last time in that location was this much carbon dioxide (CO2) in the Earth'southward atmosphere, modern humans didn't be. Megatoothed sharks prowled the oceans, the world'due south seas were up to 100 anxiety higher than they are today, and the global boilerplate surface temperature was up to 11°F warmer than information technology is now.

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

According 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 peak in the Northern Hemisphere, although information technology is more likely to take a couple more years until it stays in a higher place that threshold, according to Ralph Keeling, a researcher at the Scripps Institute of Oceanography.

CO2 levels are far higher at present than they have been for anytime during the by 800,000 years.
Click image to enlarge. Credit: Scripps Institution 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 of import long-lived global warming gas, and once it is emitted past burning fossil fuels such as coal and oil, a single CO2 molecule tin remain in the atmosphere for hundreds of years. Global CO2 emissions reached a record high of 35.6 billion tonnes in 2012, up 2.6 per centum from 2011. Carbon dioxide and other greenhouse gases warm the planet by absorbing the sun'due south free energy and preventing heat from escaping dorsum into infinite.

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

There is no single, agreed-upon answer to those questions as studies evidence a wide date range from between 800,000 to 15 million years ago. The near direct evidence comes from tiny bubbling of ancient air trapped in the vast ice sheets of Antarctica. By drilling for ice cores and analyzing the air bubbling, scientists accept found that, at no point during at least the by 800,000 years have atmospheric CO2 levels been as high equally they are now.

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

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

Other inquiry, though, shows that yous accept to go back much farther in time, well beyond 800,000 years ago, to find an instance where CO2 was sustained at 400 ppm or greater.

For a 2009 study, published in the journal Science, scientists analyzed shells in deep body of water sediments to estimate past CO2 levels, and plant that CO2 levels take not been equally high equally they are at present for at least the past 10 to xv one thousand thousand years, during the Miocene epoch.

"This was a time when global temperatures were substantially warmer than today, and there was very little ice effectually anywhere on the planet. And and so ocean level was considerably higher — around 100 feet college — than it is today," said Pennsylvania Land University climate scientist Michael Mann, in an email conversation. "It is for this reason that some climate scientists, similar James Hansen, take argued that fifty-fifty current-day CO2 levels are too high. In that location 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, equally ice sheets melt and seas expand due to rise temperatures. Scientists are projecting upwardly to 3 anxiety or more of global sea level rise by 2100, which would put some coastal cities in peril.

While there have been past periods in Earth's history when temperatures were warmer than they are now, the rate of modify that is currently taking place is faster than virtually of the climate shifts that have occurred in the past, and therefore information technology will probable be more difficult to adjust to.

A 2011 written report in the journal Paleoceanography plant that atmospheric CO2 levels may take been comparable to today's as recently as sometime between ii and four.6 million years ago, during the Pliocene epoch, which saw the arrival of Man habilis , a possible ancestor of modern human being sapiens, and when herds of giant, elephant-like Mastadons roamed Due north America. Modern human civilization didn't go far on the scene until the Holocene Epoch, which began 12,000 years ago.

Regardless of which estimate is correct, information technology is clear that CO2 levels are at present higher than they have ever been in mankind'south history. With global CO2 emissions standing on an upward trajectory that is likely to put CO2 concentrations higher up 450 ppm or higher, it is extremely unlikely that the steadily rising shape of the Keeling Curve is going to alter anytime soon.