WASHINGTON – Worldwide levels of the chief greenhouse gas that causes global warming have hit a milestone, reaching an amount never before encountered by humans, federal scientists said Friday.
Carbon dioxide was measured at 400 parts per million at the oldest monitoring station in Hawaii that sets the global benchmark. The last time the worldwide carbon level was probably that high was about 2 million years ago, said Pieter Tans of the National Oceanic and Atmospheric Administration.
That was during the Pleistocene Era. It was much warmer than it is today, Tans said.
The measurement was recorded Thursday and it is only a daily figure; the monthly and yearly average will be smaller. The number 400 has been anticipated by climate scientists and environmental activists for years as a notable indicator, in part because it’s a round number – not because any changes in man-made global warming happen by reaching it.
Physically, we are no worse off at 400 ppm than we were at 399 ppm, Princeton University climate scientist Michael Oppenheimer said.
But as a symbol of the painfully slow pace of measures to avoid a dangerous level of warming, it’s somewhat unnerving.
Environmental activists, such as former Vice President Al Gore, seized on the milestone.
This number is a reminder that for the last 150 years – and especially over the last several decades – we have been recklessly polluting the protective sheath of atmosphere that surrounds the Earth and protects the conditions that have fostered the flourishing of our civilization, Gore said in a statement.