Summer is upon us, unofficially at least. So to usher in the driving season, may I introduce, a new way to offset your personal carbon emissions from driving — as well as from flying, and heating, cooling, and powering your house.

Obviously, isn’t the only carbon offset program in town; Terrapass is more established and better known. But one thing about is unique: it’s cheap. I mean, really, really cheap. A ton of CO2 costs just $5.50 U.S., which is, oh, about a quarter of the current price on the European Union carbon futures market, and substantially less than other carbon offset programs I’ve found (see here and here for a rundown).

In fact, is so cheap it made me wonder: is it for real? With some caveats, I’m inclined to think it is.

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The real question in figuring out whether could be real is this: is it really possible to reduce U.S. carbon emissions by one ton for the low, low price of $5.50? I don’t see why not.

Here’s how it works: invests in energy efficiency, in solar and wind power, and in tree-planting projects. And those projects either offset electricity that would have been generated from fossil fuels (coal and natural gas, mostly) or capture carbon from the atmosphere and sequester it in trees and forest soils.

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Let’s leave aside tree planting for the moment. On energy efficiency and renewables: there are a lot of projects that are almost, but not quite, at the financial break-even point, the place where it makes sense to make the energy-efficient investment, but all that’s needed is a little extra cash to push them over the top. That’s especially true given that the rapid runup in the price of fossil fuels means that renewables are becoming very cost competitive. Sometimes a small investment is all that’s needed to make a financially marginal wind or solar project pencil out.

Which all means that there’s a lot of low-hanging fruit — that is, efficiency & renewables projects that are just on the cusp of making sense on purely financial grounds, where only a few extra dollars can turn them from an idea on the drawing board into reality. So the idea of something like Carbonfund, I suppose, is to find good projects that are just on the verge of beating out business as usual, and providing that extra bit of cash that’s needed to make the accounting department give the green light.

Now, over time, the price of a ton of carbon is bound to climb, as the low-hanging fruit gets plucked. But for now, I can believe that there are plenty of opportunities to reduce CO2 emissions at $5.50 per ton.

RealClimate has a great discussion of the program, including some caveats — especially about reforestation projects, for which carbon storage can apparently be hard to measure and verify.

Now, I know that some people have criticized these sorts of programs as the climate equivalent of buying indulgences — we sin, we pay a sin tax, and forget about it; but we don’t really change our ways. Under this view, a better and more honest step to reducing our own carbon emissions is, well, to reduce our own carbon emissions — not to pay someone else to do it for us.

There’s a valid point there. But I think it’s a little misguided. I mean, why spend thousands to reduce my own personal emissions by a little bit when the same investment, pooled together with investments from other people and directed by people who really know what they’re doing, would make a much, much bigger difference? This may be a case where effectiveness, rather than purity, is the real sign of personal virtue.

(Tip of the hat to Dave Manelski)