Pretty much every recent news article you’ve read about the global warming impact of methane compared to carbon dioxide is wrong. Embarrassingly, everyone from the Environmental Protection Agency itself to the New York Times and Washington Post and Wall Street Journal continue to use lowball numbers that are wrong and outdated. In fact, as we’ll see, they are doubly outdated.Here, for instance, is the New York Times from Tuesday: “Methane, which leaks from oil and gas wells, accounts for just 9 percent of the nation’s greenhouse gas pollution — but it is over 20 times more potent than carbon dioxide, so even small amounts of it can have a big impact on global warming.”
Here is the EPA’s own news release from Tuesday on its on its proposed new methane rule: “Methane, the key constituent of natural gas, is a potent GHG with a global warming potential more than 25 times greater than that of carbon dioxide.”
In fact, two years ago the Intergovernmental Panel on Climate Change (IPCC) reported in its definitive Fifth Assessment of the scientific literature (big PDF here) that methane is 34 times stronger a heat-trapping gas than CO2 over a 100-year time scale, so its long-term global-warming potential (GWP) is 34. That is a nearly 40 percent increase from the IPCC’s previous estimate of 25.
GWP CH4The global-warming potential of methane compared to CO2 over 20 years and 100 years, with and without climate-carbon feedbacks (cc fb). Via IPCC.
If you think that the 20-year GWP (86) might actually be more relevant in a world where we are only decades away from crossing points of no return for key climate impacts, you aren’t alone.
The fact is the 100-year potential has been used in part because scientists have been focused on the long-term warming impact — and the year 2100 is an endpoint for much analysis. But after ignoring the scientists for 25 years, the world really needs to worry that we are likely to cross dangerous tipping points long before then, including the irreversible loss of enough ice on Greenland and Antarctica to raise sea levels perhaps 40 feet or more.
And although the 100-year GWP is by far the most widely used, the IPCC itself drops this mini-bombshell in their 2013 report:
There is no scientific argument for selecting 100 years compared with other choices (Fuglestvedt et al., 2003; Shine, 2009). The choice of time horizon is a value judgement since it depends on the relative weight assigned to effects at different times.
Again, there is no scientific reason to pick the 100-year GWP over the 20-year GWP. The EPA and media outlets should in fact make clear they are talking about the 100-year GWP, and the best media coverage should give the 20-year GWP, since that number is increasingly relevant for humanity.
Returning to the main point, the EPA and New York Times and most other major media outlets are using the wrong global warming potential — one that could easily be fact-checked. How easily? Just Google “global warming potential.” The Wikipedia entry pops up first and in the opening paragraph explains “In the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, methane has a lifetime of 12.4 years and with climate-carbon feedbacks a global warming potential of 86 over 20 years and 34 over 100 years in response to emissions.”
The bottom line is that methane is a superpotent greenhouse gas — especially over the medium-term, a timeframe of growing concern to scientists. The media needs to start getting its facts straight, especially since we know that methane leaks from the entire natural gas lifecycle from fracking to combustion significantly undercut or eliminate any meaningful climate benefit from the fracking boom (see my 2014 post “By The Time Natural Gas Has A Net Climate Benefit You’ll Likely Be Dead And The Climate Ruined”)
Press link for more: Joe Romm | thinkprogress.org