Methane is More Potent
Methane captures much more heat than carbon dioxide. But it degrades within a few years. While it is present in the atmosphere, it heats the planet 80 – 90 times as much as CO2
Methane captures much more heat than carbon dioxide...
As long as methane is present in the atmosphere, it heats the planet up to over 80 times as strongly as CO2. How exactly methane’s heating contribution compares to CO2 depends on the time frame. The graph shows how this comparison develops over time (source).
“Instantaneous Global Warming Potential (GWP)” is the warming effect of methane when first emitted into the atmosphere. As you can observe in the graph, after 20 years, the comparison between methane and CO2’s warming contribution gives a figure that is closer to 80 times that of CO2. It’s important to note that at that point in time, twenty years after it was emitted, most of the methane in the atmosphere had already broken down into CO2 and water.
The 20-year figure shows the average heating impact over 20 years, which is known as Global Warming Potential 20 (GWP20). While methane is intact, the effect is much greater; in the years after it has been degraded, it is much less. On average, its heating effect is over 80 times that of carbon dioxide in the first 20 years, but the effect is strongly front-loaded.
The above graph also takes into account the heating effect of ozone (which methane degradation causes) and water (into which methane degrades), and adds them up to arrive at one integrated figure of methane’s heating impact.
Adding these effects together, it’s clear that while it persists in the atmosphere,
methane is massively more potent than CO2.
Yet in most discourse about climate change, including IPCC reports, methane’s warming effect is still represented over a period of 100 years, or GWP100. This is misleading because after 30 years, less than 10% of the emitted methane persists in the atmosphere. The GWP100 convention effectively “waters down” the heating impact of methane, diluting its substantial impacts in the years after it’s first emitted over most of the rest of the century when it’s not there anymore.
Climate tipping points respond to actual temperatures, not to statistical averages over a hundred years into the future. For this reason, the GWP100 convention has been criticised by leading scientists and organisations, and we join them in calling on the UNFCCC to use GWP20 alongside GWP100 as a standard in greenhouse gas accounting (“dual accounting”).
Although GWP20 is better for characterising methane’s contribution to current temperatures, it still underestimates methane’s heating effect in the near term. Since climate tipping points are emerging faster than scientists previously thought possible, and since actual temperatures in real-time drive extreme weather events, we need to consider methane’s immediate heating effects, as well as its Global Warming Potential (GWP) values for 20 and 100 years. This is important for accurately assessing methane emissions’ damage to the climate and appropriately prioritising methane emissions cuts.