What is the most problematic greenhouse gas?

Kathryn Harkup and Peter Haynes answered this question...

Chris - Kathryn, let's come back to you. We've heard from Phoebe who has written to us to say, " I've read that methane is a worse greenhouse gas than carbon dioxide, but why is this? Is that something to do with its molecular structure?"

Kathryn - To be honest, that would be a question for a climate scientist. There are chemical differences between methane and carbon dioxide. Methane is rather more inert than carbon dioxide, but depending on the circumstances, however, the atmosphere is a very different environment and there are all sorts of things going on in that environment that are very different to down on the ground. So what is going on with methane and carbon dioxide? I think Peter would actually be in a better position to answer.

Peter - The common feature of these two gases is that the molecules there is sort of several atoms. There's three atoms in carbon dioxide, there are five in methane. And, that means that they can vibrate at frequencies, which are relevant to absorbing infrared radiation, absorbing heat radiation. So they can both absorb radiation and also re-emmit it. It's those sorts of differences that determine how effective the greenhouse gas is. There are also other effects, like for example, what are called "window effects". That if something absorbs in a wavelength, which other molecules don't absorb in, it's overall effect can be more powerful than you can ever thought. So these things can be weighed against each other.

Chris - So if I've got a whole heap of methane, is my best option then to set fire to it? Because it will be better for the environment to do that than to leave it as methane in the atmosphere.

Peter - I would say almost certainly not. Right, <laugh> , there's something which we talk about as a "lifetime" . If I put a molecule of carbon dioxide in the atmosphere, then it stays in the atmosphere for hundreds or thousands of years until they're probably absorbed by sort of geological processes. Actually, if I've got met into the atmosphere, there are chemical processes that break it down. So all of those things have to be taken into account when you are sort of comparing the merits or demerits of different molecules.

Chris - So short term yes. Long term, probably not then. Yeah. That's right. Yep. Thank you for that.