350 is the red line for human beings, the most important number on the planet. The most recent science tells us that unless we can reduce the amount of carbon dioxide in the atmosphere to 350 parts per million, we will cause huge and irreversible damage to the earth.
In this exclusive lecture for Sydney Ideas leading environmental writer and activist Bill McKibben talks about how climate science and climate politics are quickly evolving–and how we now have a much more specific idea both of the peril we face and the steps (large and difficult) necessary to solve it.
Even two years ago, scientists could offer only vague ideas of how much carbon in the atmosphere was too much. But in the wake of the rapid melt of Arctic sea ice in 2007, it's become clear that this is a problem not for the future but very much for the present.
In addition, McKibben describes the swelling grassroots global movement, 350.org, which looks set to coordinate the largest day of global environmental action ever, with actions from high in the Himalayas to underwater on the Great Barrier Reef.
Bio
Bill McKibben
Environmentalist Bill McKibben is a scholar in environmental studies at Middlebury College.
McKibben is an American environmentalist and writer who frequently writes about global warming, alternative energy, and the risks associated with human genetic engineering. Beginning in the summer of 2006, he led the organization of the largest demonstrations against global warming in American history. McKibben is active in the Methodist Church, and his writing sometimes has a spiritual bent.
He is the author of The End of Nature (1989), the first book for a general audience about global warming. Recent books include Enough (2004), which critiques human genetic engineering and other rapidly advancing technologies; Wandering Home (2005), which catalogs his foot-travels across the Vermont landscape; and Age of Missing Information (2006), in which he compares his experience watching 1700 hours of videotaped TV to that of contemplating nature in the Adirondacks.
The argument that manmade CO2 emissions will lead to a catastrophe is based on a three step argument.
1. CO2 has a first order effect that warms the planet
2. The planet is dominated by net positive feedback effects that multiply this first order effect 3 or more times.
3. These higher temperatures will lead to and already are causing catastrophic effects.
You are dead right on #1, and skeptics who fight this are truly swimming against the science. The IPCC has an equation that results in a temperature sensitivity of about 1.2C per doubling of CO2 as a first order effect, and I have found little reason to quibble with this. Most science-based skeptics accept this as well, or a number within a few tenths.
The grand weakness of the alarmist case comes in #2. It is the rare long-term stable natural physical process that is dominated by positive feedback, and the evidence that Earth’s climate is dominated by feedbacks so high as to triple (in the IPCC report) or more (e.g. per Joe Romm) the climate sensitivity is weak or in great dispute. To say this point is “settled science” is absurd.
So thus we get to the heart of the dispute. Catastrophists posit enormous temperature increases, deflecting criticism by saying that CO2 as a greenhouse gas is settled. Though half right, they gloss over the fact that 2/3 or more of their projected temperature increase is based on a theory of Earth’s climate being dominated by strong positive feedbacks, a theory that is most certainly not settled, and in fact is probably wrong. Temperature increases over the last 100 years are consistent with neutral to negative, not positive feedback, and the long-term history of temperatures and CO2 are utterly inconsistent with the proposition there is positive feedback or a tipping point hidden around 350ppm CO2.
So stop repeating “settled science” like it was garlic in front of a vampire. Deal with the best arguments of skeptics, not their worst.
member. 
