For decades the primary way environmentalists concerned about manmade global warming have advocated to slow it has been to reduce human emissions of the “greenhouse gas” carbon dioxide (mainly from burning coal, oil, and natural gas for energy). Lately they have focused increasingly on contributions from two other “greenhouse gases,” primarily from agriculture—methane (CH4) from livestock flatulence, and nitrous oxide (N2O) from chemical fertilizers.

Why? Because CH4’s forcing effect (the amount of infrared radiation, or heat, each molecule in the atmosphere impedes from escaping from Earth’s surface to space, thus warming the surface) is 30 times, and N2O’s 230 times, that of CO2, as illustrated here:

Why? Because almost all the outgoing longwave radiation (infrared) in the frequency bands CO2 can absorb has already been absorbed—by both CO2 and water vapor (H2O)—while far less in the bands CH4 and N2O can absorb has already been absorbed. So we say CO2’s bands are nearly “saturated,” while CH4’s and N2O’s are nearly “transparent.”

So, it looks like we should be much more concerned about N2O than about CO2 or even CH4. Or should we?

The rate at which we’re adding CO2 to the atmosphere is about 3000 times that at which we’re adding N2O, and 30 times that at which we’re adding CH4, as illustrated here:

Consequently—because CO2’s rate of increase in the atmosphere is so much faster than CH4’s or N2O’s—the contribution to forcing (and so to global average temperature) from CO2 is about 10 times that from CH4 and 13 times that from N2O, as illustrated here:

So, should we reduce CH4 and N2O emissions (by reducing agricultural production) to slow global warming?

As atmospheric physicist and MIT emeritus professor of meteorology Richard Lindzen put it in a talk to Irish beef farmers February 27, “shutting down emissions of CH4 and N2O globally (forget little Ireland) will have no discernible impact on the climate metric regardless of what you believe about global warming and which model you are using.”