Is Gas Just as Bad as Coal?

I’m part of an online debate at Slate this week over the future of climate policy. My initial contribution covers a lot of territory, but the editors (who got to pick the title) zeroed in on my exhortation not to screw up shale gas. The upshot is that there’s been some interesting pushback.

In particular, some commenters (responding to a reprint of the piece over at Mother Jones) have raised the question of whether, once you include emissions not only from power generation but also from production and distribution, gas might actually be just as bad as coal. They point to an analysis (just updated earlier this week) by Cornell professor Robert Howarth claiming that when you account for the whole “lifecycle” of natural gas – particularly the release of methane into the atmosphere – it’s actually worse than coal.

It’s important to account for the full lifecycle, but I’m skeptical, for two pretty simple reasons. (I’m actually skeptical for a third – Howarth doesn’t distinguish between domestic production and LNG – but that’s more complicated.) As someone at Worldwatch pointed out when Howarth released his preliminary analysis earlier this year, he’s comparing apples and oranges. In particular, Howarth completely ignores the fact that coal mining generates greenhouse gas emissions too. When those are included, natural gas is clearly better than coal, as this CMU analysis (PDF) shows.

The CMU analysis also makes another important technical decision that clarifies the advantage of gas over coal: it uses what’s called a 100-year global warming potential for methane, rather than the 20-year potential that Howarth uses. (The paper isn’t explicit about that choice, but if you dig into the references, you can find it.) What does this mean in something vaguely resembling English? Methane doesn’t stay in the atmosphere for as long as carbon dioxide does. What Howarth is doing is largely ignoring that. The result is a three-fold increase in the calculated impact of methane leaks. One can make a case for that choice if you’re trying to get greenhouse gas concentrations down very quickly. But as far as long-term concentrations (which are the primary focus for policy) go, that’s the wrong choice.

To be sure, there are plenty of opportunities to reduce methane emissions from natural gas production and distribution, and we should be pursuing whichever ones are cost-effective. And there are other, I think bigger, challenges associated with natural gas, including local  impacts in particular. I’ll leave those for another post.