How much is 4.5 million?

Flipping through my NYT this morning, I noticed that Toyota has an ad proclaiming their millionth Prius sold. Which they claim means that 4.5 million tons of CO2 emissions have been avoided. How much is that? Let's put it in perspective.

Well, in what I think is one of the clearest, simplest, most useful academic formulations of the scope of the climate challenge, Robert Socolow from Princeton uses the concept of the "stabilization wedge." The basic idea is that business-as-usual sees the atmosphere's CO2 intensity climbing through mid-century, but we actually need it reduced by mid-century, so if you can picture it in your mind or click on the link, on a graph of CO2 intensity on the y-axis and time on the x-axis, three points form a triangle: where we are now, where we are headed, and where we need to be headed. Things we do to reduce CO2 emissions can be thought of as wedges taken out of that triangle. The good news is that Socolow identifies enough existing technologies that can be deployed on a large enough scale to cover the necessary stabilization wedges. The bad news is that none of them are very easy at all. You can of course chop it up any way you see fit, but Socolow defines one stabalization wedge as 1 billion tons of CO2 avoided per year by 2050 - that is, by 2050, whatever you did to get that wedge has to be saving you 1 gigaton of CO2 emissions every year. We need somewhere between 10 and 20 of those.

So where does that millionth Prius leave us? 4.5 million tons is about one half of one percent of a wedge. Oh, and that's only if it's all CO2 avoided in a single year. Which it isn't. Happy Thursday.

No no, I shouldn't do that. The good news is that hybrid sales have accelerated every year, so I'm guessing that, if their 4.5 million figure is accurate (who knows, it's advertisement), the existing Prius fleet is probably saving something like 2 or 3 megatons a year right now. And the fleet is growing. And hybrids are getting cheaper and better. So this is really just another data point with the same bottom line: we can beat this, but we really really need to get on it. Think kitchen sink, people. Kitchen sink.