Posted by: ericgrimsrud | April 1, 2016

The other half of greenhouse gas warming

We are well aware of the amount of our major long-lived greenhouse gas, CO2, that has been emitted into our atmosphere. That quantity has been easy to track either from the amount of fossil fuels we burn each year and/or by direct measurements of CO2 in the atmosphere. We also know that there are at least two other permanent greenhouse gases in our atmosphere – methane (CH4) and nitrous oxide (N2O) – that also contribute significantly to global warming.  Although their concentrations in the atmosphere are much lower than that of CO2, on a molecule-to-molecule basis each of these are much stronger greenhouse gases – 28 times stronger than CO2 in the case of CH4 and 270 times stronger in the case of N2O.  Because the sources and sinks of these two GHG’s are more numerous and complex than those of CO2, it has been more difficult, to date, to estimate their quantitative effects on warming relative to that of CO2.

This has now been done, however, in a new study recently reported in Nature (a summary of it is available to the public at  The answers they provide are that CH4 emissions are causing about 40% as much warming as the CO2 resulting from fossil fuel combustion and that N2O is causing about 20% as much. Most of the CH4 and N2O emissions are attributed to agricultural practices.  Methane is formed in the ruminant stomachs of livestock and in the anaerobic decay of their waste products as well as by rice cultivation in wetlands.  Nitrous oxide is produced from the application of nitrogen-based fertilizers and from the burning of plant and animal wastes.  By the conversion of forests to tillable fields, agricultural practices also add more CO2 to the atmosphere – enough to additionally heat the Earth by about another 30%.  Putting all of this together, the sobering conclusion is that present agricultural practices result in approximately the same amount of global warming as caused by the combustion of fossil fuels.  Note also that a significant fraction of our total fossil fuel combustion is dedicated to energy intensive aspects of agriculture including beef and fertilizer production.

Although this conclusion might not be surprising to scientists, the general topic has not received nearly enough attention in the past. Although it is hard enough to wean the world of its addiction to fossil fuel combustion, it is probably even more difficult to change its means of food production.  Agriculture without bovine cattle and nitrogen-rich fertilizers would constitute great changes in existing practices.

Nevertheless, it is becoming increasingly clear that we have two equally important challenges to face in the battle against climate change. One is how to power our multitude of activities by methods other than fossil fuel combustion and the other is how to feed ourselves by methods not involving bovine cattle and nitrogen-rich fertilizers.  Since I know many healthy, happy people that manage to do both of these things, it is clearly possible and would be made much easier for everyone to do if they had the help of an organized and wise government.  “But this is not going to happen”, I can already hear you say.  OK, then how about getting ready for a 4-degrees C warmer world with the sea covering all coastal cities and land.  All of this is frightening enough to turn a person into a denier of science and the forces of Mother Nature – which it is possibly doing at this moment.

Again, we need either much better/smarter people or a strong carbon tax. A stiff carbon tax will not only reduce our use of fossil fuels but will also discourage us from the use of energy intense means of food production – such as the production of beef and nitrogen-rich fertilizers. In the process, sure, someone’s favorite ox is going to get gored.  But we all know that we have to modify on our current “extravagant lifestyles” so that our grandchildren can manage to have “lives”.  “The tyranny of the contemporary” (see my post in March 2016) is, indeed, a terrible force that prevents us from acknowledging and honoring our intergenerational responsibilities.



  1. Great article. I was surprised by the ~50% impact of agriculture and by the role of nitrous oxide. I just attended a panel on carbon-sequestering, no-till farming, which has come to dominate farming in this part of Pennsylvania. This 2007 NPR article makes a good case:

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