Earth Island Institute logo, tap or click to visit the Institute home page

Go Back: Home > Earth Island Journal > Latest News > Post and Comments

Latest News

Methane’s Contribution to Global Warming is Worse than You Thought

To tackle climate change, we need more honest accounting of this potent greenhouse gas

“Methane is 21 times more heat-trapping that carbon dioxide.” If you’re a frequent reader of environmental websites, no doubt you’ve seen some version of that sentence many times. The “twenty-times” figure is the most common way of explaining how methane (or CH4, or uncombusted natural gas) reacts in the atmosphere.

Just one problem: It’s not entirely accurate – at least not in the time-scale we should be using to think about how to tackle greenhouse gas emissions.

Actually, any CH4 released today is at least 56 times more heat-trapping than a molecule of CO2 also released today. And because of the way it reacts in the atmosphere, the number is probably even higher, according to research conducted by Drew Shindell, a scientist at NASA’s Goddard Space Center. So why is the 21 times figure the one that gets bandied about? Because methane breaks down much faster than carbon dioxide. While CO2 remains in the atmosphere for at least a century (and probably much, much longer, according to Stanford’s Ken Caldeira), CH4 lasts only about a dozen years. When the Intergovernmental Panel on Climate Change had to come up with a way for comparing different greenhouse gases, it decided to use a century baseline to calculate a molecule’s “global warming potential.”

See this graph on global warming potential values for some key GHGs by the GHG Management Institute (you'll have to scroll down a bit to get to it)

While these various comparisons are well understood by climatologists and climate change policy wonks, I’m guessing they’re not that well known among the general public.

Why does it matter? Because we don’t have a century to get serious about the impacts of runaway greenhouse gas emissions. Climate change is upon us now. And we appear to be approaching some irrevocable tipping points that will create powerful positive feedback loops, the most worrisome being the release of methane stores at the bottom of the ocean and locked into sub-Arctic permafrost.

Carbon dioxide’s longevity means that the warming we’re experiencing now is actually the result of fossil fuel burning that happened a generation ago. And the emissions we’re causing today won’t be felt for decades to come. At our current rate of emissions, we’ll be toast 100 years from now.

What if we were to use the IPCC’s 20-year comparison instead of its 100-year comparison? For starters, it would force us to get much more serious about tackling  the sources of methane emissions. Here in the US, the top methane sources are the decomposition of wastes in landfills, agriculture (from ruminant digestion), and leaks from natural gas drilling and transmission. A new emphasis on methane would require us to get smarter about capturing methane at landfills, reduce the market incentives that encourage Americans’ meat-heavy diets, and ensure that methane isn’t leaking from fracking operations.

But beyond the policy specifics, adopting the 20-year global warming potential comparisons would be useful for changing how we think about climate change.

In his much discussed Rolling Stone essay, Bill McKibben lays out three numbers everyone should know to understand the global warming threat. Two degrees centigrade – the global average temperature increase we dare not cross; 565 gigatons – the amount of CO2 we can afford to emit and still stay within that temperature; and 2,795 gigagtons of CO2 – the amount of fossil fuel reserves we know we have. But there are some numbers McKibben neglected: the numbers on the calendar, figures like 2022, 2032, 2112. These are just as important to keep in mind. If scientists and policy makers (and journalists and advocates) continue use a century-mark to measure and compare emissions, well then it seems like we have plenty of time; complacency remains an option. If we use the 20-year measurements, the immediacy of the global warming threat is more apparent.

We’re running out of time, and the luxury of fudging the numbers. Which is reason enough for me to start making sure that whenever I’m writing about methane emissions, I’ll be using a different set of figures from now on.

Jason MarkJason Mark photo
Jason Mark is the Editor in Chief of SIERRA, the national magazine of the Sierra Club, and the author of Satellites in the High Country: Searching for the Wild in the Age of Man. From 2007 to 2015 he was the Editor of Earth Island Journal.

Email this post to a friend.

Write to the editor about this post.

Subscribe Today
cover thumbnail EIJ cover thumbnail EIJ cover thumbnail EIJ cover thumbnail EIJFour issues of the award-winning
Earth Island Journal for only $15



Everyone in the world fart at once and lets see what happens .lmao

By uppyurarse on Fri, February 19, 2016 at 11:11 am

This is especially relevant to hydroelectricity, which is often held up as a great example of Green Energy. It is not.

Especially in shallow tropical reservoirs (but elsewhere as well - there’s research in Canada too) hydro dams produce massive amounts of CH4 (methane).

Even taking the IPCC’s figures, which equate the climate change effects based on 100 years, this means that the kinds of dams built in the Amazon contribute more to climate change than if they would generate the same power from fossil fuels. The Belo Monte dam will be the 3rd largest in the world. It needs to be stopped, and Brazil needs to be shamed into abandoning its plans for 60 more huge dams which will turn the Amazon into nothing more than a series of fetid reservoirs.

By Patrick Cunningham on Wed, August 22, 2012 at 2:57 am

I think you mean positive feedback loops kicking in..

<a href=“”></a>

By prokaryotes on Tue, August 21, 2012 at 1:31 pm

Thanks for this article. I’ve reblogged your post here and added a video about permafrost methane (2010) ...

By prokaryotes on Tue, August 21, 2012 at 11:34 am

Thanks for pointing out that the standard GWP of still being applied to methane is wrong.

The IPCC has it at 72 over 20 years so I have been using at least.
Over methane’s lifetime it is 100.

A Perspective Paper on Methane Mitigation as a Response to
Climate Change
Daniel J.A. Johansson, Fredrik Hedenus 2009
Methane is a considerably stronger greenhouse gas then carbon dioxide. For short time horizons (less than 10 years) the effect on the temperature is about 100 times as strong for equally sized emission pulses.
An emission pulse of methane has an effect on the global average surface temperature far longer in time than the atmospheric perturbation life-time of methane. This is due to inertia in the climate system.
Even though the temperature response of a methane pulse lingers on for more than a century, the effect on the temperature decays considerably faster than for an emission pulse of carbon dioxide.

It was a mitigation policy decision to defer the GWP of methane over 100 years- not strictly science. As you say what is needed is a GWP for methane emissions.

As post 2007 we have a renewed fast sustained atmospheric methane increase due to feedback emissions, we are in an emergency situation on methane.

As this situation is being ignored we are presently committing all life to runaway rapid warming. This is because global warming commitment today is several times today’s warming- that is causing the planet to emit large amounts of methane- and the Arctic summer sea ice is past tipping point. 

The correct GWP to use is 100. Otherwise the methane feedback planetary emergency will continue to be ignored and the world is over.

By Peter Carter on Tue, August 21, 2012 at 9:53 am

Leave a comment

Comments Policy

Remember my personal information?

Notify me of follow-up comments?

Please enter the word you see in the image below:

View Posts by Date View Posts by Author


Four issues for just
$15 a year.

cover thumbnail EIJ

Join Now!