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MYTH #28: It’s methane


Methane is a much more powerful greenhouse gas than carbon dioxide.


Does methane trap heat? Yes. But carbon dioxide has caused three times more warming than methane.

Even though methane is better at trapping heat than carbon dioxide, there’s a lot less of it in the atmosphere. Over the last century, carbon dioxide has caused about three times more warming than methane. And sorry, we can’t duck responsibility for methane-induced warming any more than we can for carbon dioxide-induced warming. At least half of the methane in the atmosphere comes from sources like livestock (we’re not talking wild cows, here) along with coal mines and landfills.

Additional info from the Union of Concerned Scientists

CO2 has caused most of the warming and its influence is expected to continue.

CO2, more than any other driver, has contributed the most to climate change between 1750 and 2005. The Intergovernmental Panel on Climate Change (IPCC) issued a global climate assessment in 2007 that compared the relative influence exerted by key heat-trapping gases, tiny particles known as aerosols, and land use change of human origin on our climate between 1750 and 2005. By measuring the abundance of heat-trapping gases in ice cores, the atmosphere, and other climate drivers along with models, the IPCC calculated the “radiative forcing” of each climate driver — in other words, the net increase (or decrease) in the amount of energy reaching Earth’s surface attributable to that climate driver. Positive radiative forcing values represent average surface warming and negative values represent average surface cooling. CO2 has the highest positive radiative forcing (Figure 1) of all the human-influenced climate drivers compared by the IPCC. Other gases have more potent heat-trapping ability molecule per molecule than CO2 (e.g. methane), but are simply far less abundant in the atmosphere and being added more slowly.

Figure 1: Carbon dioxide (CO2), more than any other climate driver, has contributed the most to climate change between 1750 and 2005.

CO2 sticks around.

CO2 remains in the atmosphere longer than the other major heat-trapping gases emitted as a result of human activities. It takes about a decade for methane (CH4) emissions to leave the atmosphere (it converts into CO2) and about a century for nitrous oxide (N2O). In the case of CO2, much of today’s emissions will be gone in a century, but about 20 percent will still exist in the atmosphere approximately 800 years from now. This literally means that the heat-trapping emissions we release today from our cars and power plants are setting the climate our children and grandchildren will inherit. CO2’s long life in the atmosphere provides a clear rationale for reducing our CO2 emissions without delay.