High on Mount Mauna Loa in Hawaii history is being made. In a weather observatory run by the US National Oceanic and Atmospheric Administration, scientists are recording concentrations of carbon dioxide in the atmosphere higher than they’ve been for at least three million years.
The concentrations are now verging on the symbolically important level of 400 parts per million. That compares to 317ppm in 1958 and around 280ppm at the dawn of the Industrial Revolution in 1780.
Further back concentrations varied naturally between about 200ppm during ice ages and around 300ppm during the warmer periods between ice ages. But according to scientists from the Scripps Institution of Oceanography at the University of California, San Diego, you have to go a very long way back to find levels comparable to those being reached today.
Geochemical detective work suggests that that last time carbon dioxide concentrations were over 400ppm was the Pliocene Epoch. That was, the scientists point out, “three to five million years ago, before humans roamed the earth.”
The Pliocene was also a time when there was no ice at the Arctic and sea levels were maybe 40 metres higher than today. Global average temperatures were also 3-4 degrees centigrade higher.
The evidence of humanity’s recent influence on the climate is, in other words, overwhelming. In the 230 years since we started burning fossil fuels in earnest, carbon dioxide levels have risen by over 40%.
The measurements made at Mauna Loa are important because they make up the world’s longest unbroken record of carbon dioxide concentrations. They were started by Dave Keeling in 1958, and have resulted in the ‘Keeling Curve’ showing the steady increase in concentrations over the decades.
The location high in a relatively unpolluted area is crucial so that scientists can make sure that results aren’t skewed by local influences. And they are backed up by observations at other monitoring stations around the globe.
“We are creating a prehistoric climate in which human societies will face huge and potentially catastrophic risks,” said Bob Ward, policy director at the Grantham Research Institute on Climate Change at the London School of Economics. "Only by urgently reducing global emissions will we be able to avoid the full consequences of turning back the climate clock by three million years.”