The concentration of carbon dioxide in the Earth's atmosphere is about to reach 400 parts per million. Many scientists believe the "safe" level to reduce the risk of cataclysmic climate disruption is 350 parts per million.
One of the most-watched measurements in climate science is the concentration of carbon dioxide (CO2) in the Earth’s atmosphere taken at the Mauna Loa Observatory in Hawaii. Any day now, that concentration will reach 400 parts per million. You can track the latest readings at the website of the Scripps Institution of Oceanography. (And also see a great profile on the scientist behind the measurements.)
For hundreds of thousands of years prior to the rise of the human industrial economy, the CO2 level was never more than 280 parts per million. Now we are racing toward 450 and beyond.
According to a story today by Time Magazine’s Bryan Walsh, “The last time CO2 levels were this high was likely during the Pliocene epoch, between 3.2 million and 5 million years ago. The Earth’s climate was warmer during the Pliocene than it is today—perhaps by 2 to 3 C—and sea levels were much higher. It was a very different planet than the one we’ve lived on so successfully for thousands of years.”
For a discussion on why 350 parts per million was the threshold humanity did not want to cross, go here. And for a very sobering view of why reversing course on carbon emissions will require the biggest political movement in history, see Bill McKibben’s “Global Warming’s Terrifying New Math” article in Rolling Stone.