Why is Methane Such a Powerful Greenhouse Gas?

We need to talk about methane.

According to two recent studies, global methane levels are at an all-time high.

This is a problem because over 20 years, methane is 86 times as potent a greenhouse gas as carbon dioxide, meaning 1 tonne of methane absorbs as much heat over 20 years as 86 tonnes of carbon dioxide.

For context, this graph displays the concentration of methane in the atmosphere over the past 1000 years. Just like our carbon dioxide levels, methane levels are rising fast.

Meanwhile, the Trump Administration rolled back regulations requiring oil and gas companies to detect and seal methane leaks. This is a considerable setback as the US energy and agriculture industries are tied as the top two sources of domestic methane emissions.

One of the studies on global methane levels has a chart showing the largest sources of methane. Taken together, human activities now produce more methane than natural sources.

(The accompanying table has a detailed breakup and points out some interesting facts. For example, I had no idea that rice cultivation is a large source of methane emissions, or that termites produce so much methane.)

A Hidden Puzzle

But there’s a science question lurking here. What makes methane such a powerful greenhouse gas compared to carbon dioxide? Why do some greenhouse gases pack more of a global warming punch compared to others?

Scientists call a greenhouse gas’s power to warm the planet its global warming potential. And topping this list are greenhouse gases you might never have heard of (with names like carbon tetrafluoride or sulfur hexafluoride).

Pound for pound, these gases are many thousands of times more effective at warming the planet than carbon dioxide. Why?

The answer is surprisingly counter-intuitive: dilute greenhouse gases pack a larger global-warming punch. To see why, we need to view the world from the perspective of a beam of light.

Why A Little Bit Goes a Long Way

Earth receives energy from the Sun mainly in the form of visible light. The planet absorbs and then emits this energy into space via invisible infrared light (i.e. radiated heat). Greenhouse gases block some of this escaping infrared light, thereby trapping heat and warming the planet.

Just as there are different colors of visible light, there are different wavelengths of infrared light. One set of infrared