Before the industrial revolution, the proportion of carbon dioxide in Earth’s atmosphere hovered around 280 parts per million. In 1958, when scientists began measuring average carbon dioxide levels at an observatory on Mauna Loa in Hawaii, that figure was around 320 ppm.
This week, for the first time, the sensors at Mauna Loa have measured a daily average of more than 400 ppm.
The last time carbon dioxide levels were this high, Australopithecus was sharing the earth with mammoths and saber-tooth tigers.
Damian Carrington at The Guardian and David Biello at Scientific American have more context on the milestone and what it means. My colleague Phil Plait has debunked a ridiculous Wall Street Journal op-ed claiming that carbon dioxide levels are no big deal. All are worth reading.
For now I’ll just present you with this simple chart, which shows our stunning progress from pre-industrial carbon-dioxide levels toward the limit of 450 ppm that the Intergovernmental Panel on Climate Change has warned is necessary to have any significant hope of limiting global warming to 2 degrees Celsius.