A natural gas powered Honda Civic. Photo: Flickr, CC
Do You Smell Something?
Natural gas, which is mostly methane, is like the slightly better-behaved little brother of oil and coal. When burned, it generates fewer smog-causing emissions, and it releases less CO2 per unit of energy (the exact advantage over oil & coal depends on the source of the fossil fuels and how efficiently combustion takes place). At least, that's what most people seem to think, but as usual, reality is not so simple.
A natural gas powered Toyota Camry. Photo: Flickr, CC
The problem is that methane is a powerful greenhouse gas - much more so than CO2 - and the more natural gas you produce and distribute, the more of it will leak in the atmosphere.
This is just preliminary data, but it's pretty alarming:
[Robert Howarth, professor of ecology and environmental biology at Cornell University] is basing his conclusion on a preliminary analysis that includes not only the amount of carbon dioxide that comes out of a tailpipe when you burn diesel and natural gas, but also the impact of natural gas leaks. Methane, the main component of natural gas, is much more effective at trapping heat than carbon dioxide, so even small amounts of it contribute significantly to global warming. When you factor this in, natural gas could be significantly worse than diesel, he says. Using natural gas would emit the equivalent of 33 grams of carbon dioxide per megajoule. Using petroleum fuels would emit the equivalent of just 20 grams of carbon dioxide per megajoule.
Howarth goes further, suggesting that natural gas could even rival greenhouse gas emissions from mining and burning coal--the dirtiest of fossil fuels. He says it's "not significantly better than coal in terms of the consequences of global warming" and is calling for a moratorium on extracting natural gas from shale, which requires more energy (and so emits more greenhouse gases) than extracting it from conventional natural gas sources. (source)
If true, this means that we should immediately make big efforts to make sure that our existing natural gas infrastructure is as leak-proof as possible (something that is no doubt already done because it makes financial sense, but it can't hurt to be extra diligent), and we should be very careful about switching more transportation to natural gas. Maybe there are technical fixes to this problem and it's possible to keep methane leaks to a minimum, but for certain uses, it might be too hard and expensive to be worth it. If that's the case, better to know it now than later.
This would still leave natural gas as a cleaner source of energy when it comes to air pollution, which isn't nothing, especially in developing countries like China and India where the air is so foul and toxic in many places that cleaning it up should be a priority.
What we really need is emission free energy (or as close to that as possible). Natural gas can't offer that, so at best it could help us during a transition period.