A recent report from WWF argues that lamb stew contributes more to global warming than fish and chips or two other iconic British dishes. In many ways, sheep and cattle grazing, properly managed, seems more sustainable than dependence on ocean fish, given overfishing and the increasing temperature and acidity of the ocean caused by our excessive releases of CO2. Grazing is the original no-till (erosion-preventing) system. Where erosion isn’t a concern, rotating between perennial pastures and annual crops is a great, low-input way to control weeds, few of which can survive both grazing and tillage. Also, mixed grass-legume pastures can get most of their nitrogen from biological nitrogen fixation (the main focus of research in my lab) rather than fertilizer. These are some of the reasons why organic farmer, Jim Bender, considers grazing animals key to pesticide-free farming.
The WWF estimate of lamb’s high greenhouse-warming contribution is based on their burping and farting methane. Methane absorbs 30 times as much infrared radiation as an equivalent amount of CO2, making it a powerful greenhouse gas. But, sooner or later, methane gets oxidized to CO2 so its long-term greenhouse-gas contribution is less than the 30X-greater-than-CO2 that is widely assumed. How much less depends on how long it takes for the average methane molecule to get oxidized to CO2. Perhaps one of my dozens of readers can answer this question.
Another thing that bothered me about the WWF report is the claim that the UK needs to reduce its daily per-capita CO2-equivalent production by about 1 kg (from 5.17 kg to 4.09 kg — wow, three significant digits!) by 2030, out of a daily total of 35.6 kg. Like most economists, I think a sufficiently-large carbon tax would be the most-effective way to reduce greenhouse-gas emissions, while letting individuals decide whether they’d rather add insulation or solar panels to their homes, drive less, or eat differently. Taxing oil, coal, and natural gas wouldn’t directly penalize methane production by sheep and cattle, so maybe we’d need a separate tax on systems that produce methane. But that tax should be based on how long methane stays in the atmosphere before being oxidized to CO2, rather than on the assumption that it keeps its 30-fold greenhouse effect forever.