Methane – is it really 30 times worse than Carbon Dioxide?

Given the amount of news coverage devoted to oceanic pollution, it is not surprising that most Kiwis believe reducing waste is more important than addressing climate change.

It is also alarming, because it is wrong. Why is the message about Climate Change not getting through? Possibly because it is complicated.

Perhaps this statement will help. If we continue emitting greenhouse gases into the atmosphere, within a generation, we will have set the Planet on a course to devastation that is irreversible.

The two most important greenhouse gases are carbon dioxide (CO2) and methane. Of the two, methane is more potent, more immediate and, in the short term, more important.

It is complicated to compare gases to each other because they are all different. Different molecular weight, different half lives, different heat holding capacities. Scientists try to make things less complicated by reducing the variables. So they compare all greenhouse gases to CO2, which is used as the standard.

So a gas’s Global Warming Potential (GWP) is a comparison one ton of that gas to one ton of CO2. However, since gases survive in the atmosphere for different amounts of time, the comparison to CO2 is measured over an arbitrary time period. The time period used is generally 100 years. This is probably sensible when comparing CO2 to nitrous oxide (NO2), because NO2 survives for around 114 years, and CO2 survives for more than 500 years.

The problem is that some gases, like methane, survive for much shorter periods of time. Most methane is broken down in the atmosphere within 12 years (confusingly it mostly oxidizes to CO2, but that is another story). So when you compare methane to CO2 over a 100 year period, for the last 88 years of the comparison, there is very little methane left. This means that the vast majority of the damage done by methane happens in those first 12 years.

If you compare methane to CO2 over the standard 100 year period, methane traps 30 times more heat. But if you do a 20 year comparison, methane comes out 85 times more potent than CO2. This means that if you produce 1 ton of methane from biodegradable material by sending it to landfill, that 1 ton produces the same warming as 85 tons of CO2.

Think about that for a moment. The average household in New Zealand sends to landfill around 1 ton of biodegradable material every year, mostly food scraps, green waste and paper.

Reducing waste is a significant part of what we need to do to help save the Planet, but the most important part is understanding what types of waste we need to reduce. Diverting household bio waste from landfill is the simplest and most significant thing you can do to help.

The good news is that within 12 years the actions you take today to mitigate methane production will be felt by the Planet. That, coincidentally, is the amount of time we have left to change the course of history.

Additional Information