The atmospheric concentration of carbon dioxide, the chief greenhouse gas driving modern anthropogenic climate change, is climbing. Over the past month or so, as we've written, the carbon dioxide concentration measured at Hawaii's Mauna Loa Observatory has crept above 400 parts per million. As a round number 400 ppm is a nice symbolic marker, but as Andrew Freedman, a science reporter for Mashable, points out, at this point, every new concentration record is significant. Every single time, we're not just setting a record for the year, or the decade, or the modern era, but for the entire extent of human existence.
Humans, Homo sapiens, evolved roughly 200, 000 years ago, and we've come to dominate the planet since. The rise of civilization, the advent of agriculture, the development of science and art and philosophy have all taken place in this time. And in that entire 200,000 year stretch, and indeed for much longer, the atmospheric concentration of carbon dioxide has never pushed anywhere near where it is now. Freedman:
While the Earth's atmosphere has seen higher levels of carbon dioxide than it does now, as well as higher temperatures and far greater sea levels, those instances were due to natural drivers of climate change, such as periodic variations in the planet's orbit and in solar energy output. Scientists have studied and ruled out natural climate drivers as the main cause of global warming since the preindustrial era.
Freedman says that, though there is some uncertainty around when atmospheric carbon dioxide last hit 400 parts per million, the question is really only around how far back that window extends: “While studies show conflicting dates for when Earth's atmosphere last had carbon dioxide levels this high, estimates range from 800,000 years ago to 15 million years ago.”
We're in uncharted territory, and within a few decades, researchers say, we'll be living in an “unprecedented climate.” Global climate change is already having consequences for humans and other animals. Technology will be able to buffer us for a bit, but as science reporter Sarah Zielinski wrote recently, adapting to climate change likely won't work forever, and it certainly won't work for everyone.