By David Steele
October 26, 2009
In their article “Livestock and Climate Change,” [PDF link] Robert Goodland and Jeff Anhang have made a valuable contribution to our understanding of the causes and sources of the climate crisis. From their work, it would appear that animal agriculture is a much bigger player in global warming than even the UN FAO has estimated. While to many, their estimate that animal agriculture is responsible for 51% of global warming gases sounds wildly out of whack, in sifting skeptically through their claims, it seems to me that they’re not as far off base as you might think. Here is my take on their arguments and a conservative estimate of just what proportion of greenhouse gases must indeed flow from worldwide animal agriculture.
Goodland and Anhang’s most controversial claim is their opening salvo. The FAO, they say, has neglected the number one contribution of farm animals to the climate crisis – their breath. Farm animal breath, Goodland and Anhang figure, contributes nearly 14% of worldwide greenhouse gases, each year. Many others, however, claim that it does nothing of the sort. Animals’ breath, these critics say, is carbon neutral. Plants turn carbon dioxide into food, animals eat that food, breathe out the carbon dioxide, the plants turn it back into food and so on. Goodland and Anhang. I think, are right to challenge this conventional wisdom. Their estimate of the contribution farm animals’ breath to global warming is on the high side, though.
What we really need to consider is not the absolute amount of CO2 breathed out by the farm animals but, instead, the amount by which that number exceeds what would be pumped out if the land now used to feed the farm animals was allowed to return to nature instead. What if the plant life on which the animals feed stayed on the land, died, rotted and returned to the Earth? It turns out that estimating all the global warming gases released in the breath of farm animals versus the amount that of the wild animals and other organisms replacing them would emit if we let the farmlands lie fallow is an extremely complicated endeavor. By my reckoning, there would indeed be a lot less CO2 per unit land but putting a hard number on this CO2 from breathing is tough and fraught with error.
Fortunately, there’s another way to make the estimate. It turns out that when we let farm land return to nature, we substantially increase the ability of the soils therein to sequester carbon that plants take out of the air. Several studies have shown that some pretty simple changes in farming practices, e.g., implementing no-till farming, could increase annual soil carbon sequestration to the equivalent of 3 to 6% of all the greenhouse gasses we pump into the atmosphere each year. Letting farmland revert to meadow and forest must be at least as good.
Thus, Goodland and Anhang are onto something. In order to err on the side of caution, I’ll arbitrarily make a low estimate, 4%. One more adjustment is required. Not all of the land we currently use to raise animals could be returned to nature. We’ll need to replace the calories we get from meat with vegetable crops. Feeding ourselves with meat takes an average of at least 5 times as much plant material as eating the plants directly, so we could probably allow only 80% of the land to return to nature. Correcting for this, we get a lowball estimate of the annual contribution of farm animal breathing to global warming: 3.2%.
Goodland and Anhang estimate that converting the land used to feed animals to biofuel production, instead, would yield a net reduction of 4.2% in greenhouse gas emissions since burning carefully chosen biofuels yield 80% less CO2 than coal. This seems reasonable on the face of it. In the long run, though, it can’t be sustainable. Burning the product of the land must sooner or later lead to severe soil depletion. This can be remedied somewhat, as we do today, through the use of fertilizers but the fossil energy content of fertilizers essentially negates the global warming advantages of biofuels. There is a large and growing literature on this. So, for the short term, a 4.2% advantage is reasonable. In the long term, much less will be achievable. I’m arbitrarily setting the advantage to 1% since, realistically, I can’t see us doing much better than that in the long run. In any case, even this 1% advantage amounts to double counting, since in accounting for the changes in respiration if farmland is abandoned, I assumed an 80% reduction in farmed land.
Considering methane to be 23 times as potent a greenhouse gas as CO2, the FAO estimated that methane emissions from farm animals are responsible for 3.7% of the human-caused greenhouse effect. Goodland and Anhang very reasonably note that, over its lifetime in the atmosphere, methane as actually 72 times more potent a greenhouse gas than CO2. On that basis, they claim an additional 7.9% of net greenhouse gases are due to farm animal emissions. But they explicitly fail to adjust the greenhouse gas total to include the remaining 63% of human-caused methane that also should be counted at the 72X CO2 rate. While a precise accounting would require substantial research, given that no matter what the source, methane behaves the same way in the atmosphere, a rough calculation is not difficult. When I do the math, the net contribution of farm animal methane to total worldwide greenhouse gases works out to 6.5% in CO2 equivalents.
Animal product tonnage
The FAO uses a 2002 estimates of animal product tonnage. In 2009, that tonnage is 12% higher. Goodland and Anhang sensibly correct the GHG estimate to reflect this. Greenhouse gas estimate: add 4%.
Farm animal population
Estimates of world farm animal populations vary wildly. The FAO chose a conservative estimate of 21.7 billion. Goodland and Anhang choose a number on the opposite end of the spectrum, i.e., 50 billion. Averaging the estimates I found from various gov’t and NGO sites on the web, I come up with 27 billion. Keeping in mind that the error bars are huge, this amounts to about a 2.9% increase in the real proportion of global greenhouse gases coming from livestock.
Outdated citations and Minnesota data
The authors note that the FAO often uses old data and extrapolates the emissions from factory farm intensive Minnesota to come up with some of their worldwide estimates. Evaluating how these choices affect estimated GHG emissions will be complicated and time consuming. As the net result will amount at most to a very few percent of global warming gases, I did not attempt to carry out this complex analysis for this paper. .
Misallocated GHG accounting
The FAO excluded the emissions associated with fish farming and of wild-caught fish fed to farm animals from their estimates of animal agriculture associated GHGs. These emissions are counted in worldwide totals but not as contributions from animal agriculture. Goodland and Anhang are very much justified in allocating these emissions to the animal farming. GHG contribution: ~ 2% of the worldwide total.
Goodland and Anhang also cite higher intensities of energy use in transporting, storing, cooking and disposing of animal products than for their plant-based equivalents. They consider, also, the global warming consequences of dealing with the medical problems associated with animal consumption. As this whole area is extremely complicated and as Goodland and Anhang provide no figures to back up their claims, I think for now it is best to leave these contributions out of the equation.
Goodland and Anhang have done society a real service in their attempt to more accurately assess the degree to which animal agriculture contributes to the climate crisis. While their estimates are sometimes high, they have made a very important contribution to the debate. The public and policy makers must be made aware of the enormous consequences of our addiction to meat and other animal products. With the exception for their call for increased consumption of highly processed pseudo meats, their mitigation prescription should be heeded by all of us.
Based on my adjustments of the numbers Goodland and Anhang have provided, my conservative reanalysis of their claims indicates that animal agriculture contributes a minimum of 30.4% of worldwide greenhouse gases in CO2 equivalents.