415: The Most Dangerous Number
Last week, an exquisitely sensitive instrument located in a metal shack on the top of Mauna Loa, a 13,679-foot-high volcano in Hawaii, recorded a terrifying human achievement: Thanks to our ever-increasing addiction to burning fossil fuels, the level of carbon dioxide in the Earth’s atmosphere has risen to 415 parts per million. This is the highest level it has been since human beings have lived on Earth. And it is further evidence (as if further evidence were needed) of just how hell-bent we are on cooking the planet we live on.
For the planet itself, 415 ppm is no BFD. Over the past 4 billion years or so, it’s been much, much higher. But for us humans, 415 is a very dangerous number. The last time CO2 levels were at 415 ppm, during the Pliocene period about 3 million years ago, there was plenty of life on Earth, but the Earth itself was a radically different place. Beech trees grew near the South Pole. There was no Greenland ice sheet, and probably not a West Antarctic ice sheet, either. Sea levels were 50 or 60 feet (or more) higher.
That’s the world we’re creating for ourselves by pushing carbon dioxide levels to 415 ppm. Right now, a lot of atmospheric warming is being absorbed in the oceans. But those oceans are like a big flywheel, and the heat will be radiated out. That means, among other things, goodbye ice sheets, hello condo diving in Miami.
One way to think about carbon dioxide levels in the atmosphere is as a thermostat for the planet. As you’ll remember from third-grade science class, carbon dioxide is exhaled by animals, including humans, and inhaled by plants. It is also released when plants and animals decay, volcanoes erupt, and, most importantly, when we burn fossil fuels. Last year, we dumped about 37 billion tons of carbon dioxide into the atmosphere by burning fossil fuels. The more coal, oil and gas we burn, the faster that number rises. Before the Industrial Revolution, the level of carbon dioxide in the atmosphere was 280 ppm. Sixty years ago, it was 315 ppm. For the past few years, it has been rising by about 2 or 3 ppm a year.
https://www.rollingstone.com/politics/politics-news/climate-change-mauna-loa-carbon-dioxide-measurement-834627/