The world was abuzz last week when China and the U.S. formally joined the Paris Agreement. As the world’s two biggest emitters, this was indeed good news and a positive step forward in confronting climate change. But it was just that: a “step.” The fact is that we have postponed our response to climate change for so long that mitigation is no longer sufficient—we will have to invest heavily in adaptation too. The planet itself will underscore that fact in the coming weeks when it does something truly remarkable—and with little fanfare.
It’ll happen on a volcano in Hawaii, where a monitoring station has been recording levels of carbon dioxide in our atmosphere continuously since the late 1950s. One of the most celebrated and storied datasets for earth scientists, the Mauna Loa observatory is little known outside climate circles. But the Keeling Curve data that it has produced has been extremely influential, having first quantified humanity’s role in increasing CO2 levels in our atmosphere. And, it first documented a remarkable thing: The Earth literally “breathing” as plants grow in spring and summer and take in CO2, and then slowly release CO2 as they are harvested or die off.
CO2 levels usually bottom out in late September or early October before the “exhale” of CO2 begins. Levels at this “exhale” point have always dropped below 400 parts per million (ppm)—the milestone at which scientists say it will be difficult to keep climate change in check once crossed. In the next few weeks, when this “exhale” point is upon us once again, we could very well cross that milestone and bid farewell to a sub-400 ppm world once and for all.
It’s worth taking a moment to consider this. In the past 50 years we have increased the CO2 in the atmosphere by 30%, at a rate that continues to increase, to a level that is higher than at any time in the past 15 million years. It is as astounding as it is concerning…