The Global Warming Potential of Methane

April 2, 2021

Trivia time!

Q: Methane (CH4) is a greenhouse gas (GHGs) that absorbs heat at ___ times greater than that of carbon dioxide (CO2).

A:  a) 25

      b) 84

      c) 28

      d) 7.6

No matter what answer you chose, you are correct! This can be explained by exploring the concept of Global Warming Potential (GWP). GWPs were developed as a means to compare the effect that different GHGs have in our atmosphere relative to CO2. In general, when evaluating the climate impact that GHGs can have, we need to consider two defining features of each GHG:

1.       How well is the gas able to trap/absorb heat in the atmosphere (“radiative efficiency”)?

2.       How long does the gas last in the atmosphere (“lifetime”)?

GWPs measure the radiative efficiency or, the warming effect that one unit mass of gas has relative to a reference gas over a specified time horizon. In most cases, the Intergovernmental Panel on Climate Change (IPCC) uses CO2 as the reference gas. The resulting GWP can be used to convert a unit mass of a GHG to a carbon dioxide equivalent (CO2e) which then allows us to directly compare the climate effect of a multitude of different GHGs.

Some GHGs may last only for a short while in our atmosphere but have a much higher heat-trapping potential compared to CO2 (i.e., methane). This means that when the GWP for methane is calculated over a 20-year time period, we would see a much higher value when compared to the GWP for methane over a 100-year time period. Over the years, the IPCC has released numerous Assessment Reports which calculate the GWPs for certain GHGs and is summarized in the following table below.

Going back to the trivia question above, some of you may have realized that it is in fact a trick question because I did not attach a specified period of time to it. Under different circumstances, any one of those answers are correct. Typically, the GWPs of gases are calculated over 20-, 100- and 500-year time horizons. The vast majority of the world has adopted the 100-year period for GWPs as the standard, which has made it substantially easier for countries and governments to effectively compare emission levels across different industries and identify high-priority sectors for emission reduction opportunities.

One of the many ways that Bluesource mitigates climate impacts is through our award-winning methane program. Simply put, we take pneumatic controllers that bleed large amounts of methane into the atmosphere and we swap them for low-or-no bleed solutions. No matter what time period you use to evaluate methane’s GWP, this program has a substantial climate impact. Since 2017, our program has reduced 1.7 million tons of CO2e—a number we calculated using the 100-year GWP.

 

Table 1: Intergovernmental Panel on Climate Change IPCC Global Warming Potentials
IPCC Assessment Reports
GHG 1st WG I Report (1990) 2nd WG I Report (1995) 3rd WG I Report (2001) 4th WG I Report (2007) 5th WG I Report (2014)
20 Year Time Horizon 100 Year 500 Year 20 Year 100 Year 500 Year 20 Year 100 Year 500 Year 20 Year 100 Year 500 Year 20 Year 100 Year 500 Year
CO2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
CH4 63 21 9 56 21 6.5 62 23 7 72 25 7.6 84 28
N2O 270 290 190 280 310 170 275 296 156 289 298 153 264 300
HFC-134a 4100 1500 510 3400 1300 420 3300 1300 400 3830 1430 435 3710 1300

 

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