Tim Flannery made international headlines earlier this month when he said "the amount of greenhouse gas in the atmosphere is already above the threshold that could potentially cause dangerous climate change," and that we'd reached that point -- 455 ppm greenhouse gas equivalent -- 10 years ahead of expectations.
A scientist and the author of a book about climate change, The Weather Makers, Flannery is 2007's Australian of the Year. So it's not surprising that his remarks were heard round the world, with reports by the likes of respected news organizations like The Australian Broadcasting Corp. and Reuters appearing on dozens of news Web sites. The Daily Green published this report: Global Warming "Beyond the Worst-Case Scenario."
But the reported interpretation of the data was misleading.
Here's how it really works, according to NASA scientist Gavin Schmidt, and Flannery himself, who we asked to clarify things.
So the atmosphere has either 375 ppm and 455 ppm of carbon, depending on how you parse the terminology.
But either way, the data does not suggest we've reached a critical threshold, as Flannery was quoted as having said. And we haven't reached any milestone 10 years earlier than expected. (Nor has Flannery seen any data not widely available to other climate scientists; the upcoming Intergovernmental Panel on Climate Change report he referred to is a synthesis of previous reports released earlier this year.)
So what do the numbers really mean?
First off, they mean we've pumped an awful lot of greenhouse gases into the atmosphere. The pre-industrial level of carbon dioxide equivalent (the second, net effect kind) is estimated at 278 ppm -- so we've increased the concentration 35%.
No one knows for sure what concentration represents the danger point, when catastrophic changes will occur. Policy makers have settled on a couple. Among them: 450 ppm, which would result in a 50/50 chance that the world's average temperature would increase 2 degrees; and 550 ppm, which represents a doubling of pre-industrial levels. It could be we've already passed some important threshold.
Whatever the details, Flannery stuck to his basic thesis: That we all ought to be very concerned.
"My main point," Flannery said "is that (carbon dioxide equivalent) is already above the level any of us should be comfortable with. The widespread view that we have a decade to act is not therefore correct. We're already living with an unacceptable risk of dangerous climate change."
Schmidt was committed to clarifying the facts, but in a way he came out in the same general camp -- suggesting that a focus on exact concentrations of greenhouse gases in the atmosphere misses an important point.
"It's not that at 1.999 degrees nothing will happen and at 2.001 degrees all hell will break loose. As warming increases, effects become more severe," he said. "You have to think about it like a speed limit on the freeway. ... 55 mph is picked to try to maintain levels at a point where people aren't killing themselves every time they have a crash."
Enter your city or zip code to get your local temperature and air quality and find local green food and recycling resources near you.