550, 450, 350. The number represents how much carbon dioxide or equivalent greenhouse gas is in the atmosphere, in parts per million, and that, in turn, represents information about how global temperatures will climb, and how fast. The number we settle on should, in theory, be the level at which we're safe. It's a little like sailing toward a point on the horizon: depending on the currents, the wind, and the waves, by the time you set a course, you're blown off it, and aiming for something else.
The number's getting lower; this idea of getting to 350 is pretty new. It pushed some buttons last November, when NASA's James Hansen as part of a team of climate scientists pointed out we're around 385 parts per million of carbon dioxide in the current atmosphere, rising 2 parts per million a year. Letting that rise to 450 parts per million, they argued, would risk an ice-free planet.
Hansen's been in this game for a while; as they say on The Wire, his name rings out on the street. Twenty years ago, he presented evidence that the planet was warming. The demarcation line to avoid peril we talked about then was 550. Moving to 450 was something of a political coup. The newly-minted Obama Administration said in January the U.S. position is we want to get to 450. Around that time energy specialist, climate science advocate and blogger Joe Romm was asking whether 450 was politically possible pretty much immediately as the new president took office.
But a groundswell of support isn't a quorum - as Jefferson Smith or Frank Stoltze will tell you. Copenhagen's around the corner, and international negotiators have not, of late, expressed optimism that we're all going to get along there.
One more thing: we don't often get to report on the details of climate change studies. We've got plenty of reasons for that locally: one is that there's an ongoing discussion in our newsroom about what, exactly, we can assume people know about climate. How much explanation does it take to say that 350 parts per million is a difficult standard to imagine meeting as the population of the planet explodes? I wonder if we do tell this story right in southern California, and I wonder how we'd know.