Despite the efforts deployed to reduce greenhouse gas emissions, the levels of carbon dioxide in the Earth’s atmosphere reached a new height in April this year: an average of over 421 parts per million (ppm). Such levels have been unheard of in the past 800,000 years.
The CO2 levels in the Earth’s atmosphere, measured from the Mauna Loa observatory in Hawaii, surpassed 410 parts per million (ppm) last April. According to Ralph Keeling, the director of the Scripps CO2 programme in the Scripps Institution of Oceanography in California, this 410 ppm threshold “is important because it punctuates another milestone in the upwards march of CO2…. At the recent pace, we’ll hit 450 ppm in a mere 16 years, and 500 ppm 20 years after that. That’s well within dangerous territory for the climate system”.
Keeling’s father, Charles David Keeling, began taking the first atmospheric CO2 measures in 1958 in Hawaii: the concentration at that time was only at 315 ppm. The “Keeling curve”, the name given to the levels of carbon dioxide in the atmosphere, shows a dramatic and accelerated increase in the levels of CO2 in the atmosphere in the past 60 years. Prior to the industrial revolution, the levels fluctuated naturally over thousands of years, but we know from the ice cores that it never went over 300 ppm over the course of the previous 800,000 years (the past eight glacier cycles).
The concentrations of carbon dioxide – through which the greenhouse gas effect retains heat on our planet – were at around 280 parts per million in around 1880, at the beginning of the industrial revolution. It is thus now 46% higher. “The rise is a direct consequence of the large releases of CO2 from fossil-fuel burning,” explained the researcher to CNN. Keeling explains that the oceans and plants on earth eliminate a large proportion of the excess carbon dioxide in the atmosphere – around 50% – but now they simply cannot keep up, and the gas stays building up in the atmosphere.
The last time such levels were reached was in the middle of the Pliocene Epoch, more than 3 million years ago (when levels reached around 400 parts per million). However, at this time, the levels were steady over long periods. Nowadays, the global concentration of CO2 is rapidly increasing. During the Miocene, between 14 and 23 million years ago, the concentration of carbon dioxide in the atmosphere would have reached 500 parts per million. The Antarctic thus lost dozens of meters of ice, which in turn raised sea levels. Even further back, at the Eocene-Oligocene boundary, around 34 million years ago, the atmospheric concentration of carbon dioxide may have reached 750 parts per million. At the time, there was no ice in Antarctica.