IPCC Warns Methane Traps Much More Heat Than We Thought

[Bill USA]

http://cleantechnica.com/2013/10/04/ipcc-warns-methane-traps-much-heat-thought/

The Intergovernmental Panel on Climate Change (IPCC) reports that methane (CH4) is far more potent a greenhouse gas than we had previously realized.

This matters to the fracking debate because methane leaks throughout the lifecycle of unconventional gas. Natural gas is, after all, mostly methane (CH4).

We learned last month that the best fracked wells appear to have low emissions of methane, but that study likely missed the high-emitting wells that result in the vast majority of methane leakage. Back in August, a NOAA-led study measured a stunning 6% to 12% methane leakage over one of the country’s largest gas fields — which would gut the climate benefits of switching from coal to gas.

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... the IPCC’s latest report, released Monday (big PDF here), reports that methane is 34 times stronger a heat-trapping gas than CO2 over a 100-year time scale, so its global-warming potential (GWP) is 34. That is a nearly 40% increase from the IPCC’s previous estimate of 25.



(more)

EPA now says GW potential for methane for 100 yrs is 28-36 times that of CO2. but what is of more interest to me, considering we have a growing 'inventory' of atmospheric methane, is the 20 yr figure from IPCC of 86 times CO2's GW potential.

Of course, if it's just a matter of algebra, if CH4 has 34 times the GW potential of CO2 over 100 yrs. That would mean for 20 years CH4's GW potential would be 166 times that of CO2!

34 x 100 = 3400
3400 - 80 = 3320
3320/20 = 166

[GliderGuider]

1. The big problem is that in our current situation even the new number is too low.

Those numbers are for a slug of methane emitted into the atmosphere and then allowed to decay. This works for a methane "burst". However, what we have is a constantly rising level of methane. Under this scenario what matters is the instantaneous GWP of methane, not the 20 or 100 year GWP.

According to Drew Shindell et al, the all-in number for methane at 20 years is about 105. See the text accompanying Figure 2 on this page: http://www.sciencemag.org/content/326/5953/716.figures-only

Here's that number plotted against the IPCC's old GWP curve for methane:



You'll notice that the GWP keeps going up faster as the dwell time being considered gets shorter. So it looks like the 5-year GWP according to Shindell's calculations would be about 150. The one-year GWP that better approximates a continuous release could be higher still, possibly 200 or more.

[Bill USA]

2. A few minutes After posting OP, I added something. I think you didn't see it. Interesting given

... what you posted.

Here's what I had added:

if CH4 has 34 times the GW potential of CO2 over 100 yrs. That would mean for 20 years CH4's GW potential would be 166 times that of CO2!

34 x 100 = 3400
3400 - 80 = 3320
3320/20 = 166

[GliderGuider]

3. I'm not sure about the basis for your math, but your result is sure in the right ballpark!

[Bill USA]

4. just doing a little algebraic inference from the IPCC's Oct 2013 numbers. ...

They say methane has 34 times the heat trapping capacity of CO2 over 100 years, once methane breaks down into CO2 (after about 12 years) it obviously has the same HTC of CO2 (since it has broken down into CO2). So, over 100 yrs, you have 34 x 100 = 3400.

THen take 80 years where methane has broken down to CO2. So, that would be 1 x 80 = 80.
Subtract 80 from 3400, to get 3320 - total heat trapping capacity which applies to the other 20 years. then, divide the 3320 by 20 to get 166 - the yearly heat trapping capacity of methane for the first 20 years it's in the atmosphere.