Last week we got some bad news from a Hawaiian volcano. Not an eruption, but an emissions measurement that has far greater global significance. At a facility on Mauna Loa, instruments measured carbon dioxide levels at 400 parts per million for the first time. It’s a nice round number, and though it’s not a number activists or policymakers have fixated on (350ppm and 450ppm are the more oft-cited numbers), it’s a good chance to reflect on where we are vis-a-vis climate change. The Economist reports:
Like a birthday with a zero at the end of it, the 400ppm barrier has a psychological weight beyond any physiological significance. Although it may add a new rhetorical impetus to calls for carbon-dioxide emissions to be controlled, the argument that the risks of unfettered fossil-fuel use are too troubling to be borne was just as strong at 395ppm, or indeed 356ppm, the level at the time of the Rio “Earth Summit” in 1992; 400ppm is not a threshold. But the mere fact that the number is known—and that all the numbers for all the days for the past decades are known, too—carries with it an important lesson. To think about how to look after the planet, you need an objective measure of how it has been changing over time.
This is certainly bad news, but it’s hard to say what exactly it means. Unfortunately, our knowledge of the climate doesn’t extend far past today’s measurements. Climate models purport to explain how changes like these will affect the atmosphere, but they have to account for an immense number of variables and complicated feedback loops. It wasn’t two months ago that the Economist reported that temperatures haven’t been rising the way leading models predicted over the past decade, suggesting that we understand the impact of changes like these far less than we think we do. Given our lack of knowledge, we should avoid jumping to conclusions based on this one piece of data. That’s not a recipe for policy success.[Earth image courtesy of Wikimedia.]