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Scaling up the Methane emissions for Livestock?

March 25, 2010

LCC and Stephen Walsh discussed on March 16, March 25, March 27, and March 29

A second issue raised by Stephen Walsh about Livestock and Climate Change (LCC) is the question of "scaling up" livestock emissions of methane. The authors of LCC argue that livestock methane has been seriously undercounted. Stephen Walsh objects to this. What’s going on?

Walsh states

"The WorldWatch paper makes its second fundamental error by scaling up the impact of methane from livestock (estimated by the FAO to be about 37% of total methane from human activities) but not scaling up the impact of other sources of methane. This is an indefensible distortion of the figures."

What is this "scaling up"? LCC argues, with some justification, that methane actually has a much greater effect on the climate than current accounting methods would imply. (The basic argument is that methane has a devastating effect on climate, but a shorter half-life, so estimates of methane’s damage depends on the time frame.) Walsh doesn’t dispute this, but says that if we scale up methane from livestock, we should also do it with non-livestock methane.

His objection is not to increasing the estimates of the amount of methane from livestock, but to increasing the relative percentage.  If methane is worse than we thought, then shouldn’t this mean that the effects of both livestock and non-livestock methane need to be recalculated? And since LCC doesn’t do this, isn’t there a serious problem here? This is intuitively hard to argue against.

Following the debate on the scaling issue is difficult. Part of the problem is that there are three separate discussions going on: one concerning whether the effects of methane have been underestimated, and a second on whether livestock have been undercounted, and a third on whether we have any valid estimate at all on non-livestock methane.

Goodland’s response as to why they didn’t recalculate non-livestock methane, in effect, is that they don’t know what to recalculate. In LCC, the authors comment, "Further work is needed to recalibrate methane emissions other than those attributable to livestock products using a 20-year timeframe [the new way of counting methane]." Robert Goodland repeated this on the WorldWatch discussion forum and in his reply in the March/April 2010 issue, saying that they still haven’t found good estimates for non-livestock methane.

Walsh has a good point: it does seem to be odd to scale up livestock methane but not non-livestock methane. Walsh further disputes whether it is so difficult to estimate non-livestock methane, saying that the U. S. EPA has a figure similar to the FAO on non-livestock methane. This could be a bit circular, as the FAO report is filled with references to the EPA as a source, and the EPA report likewise frequently cites the FAO as a source. This doesn’t mean the results are necessarily corrupt — no one wants to go to extra work to "re-invent the wheel" — but that agreement between the FAO and the EPA isn’t necessarily significant.

The FAO’s figures on livestock methane really are quite suspicious. What do we make of the FAO’s statement that livestock are responsible for 37% of methane from human activities? They evidently calculated livestock methane based on per-animal estimates, multiplied by the number of animals (see p. 97 of Livestock’s Long Shadow). But we now know that their estimate of the total number of livestock was way off — the actual number is nearly three times greater. This is bound to have a huge effect on one’s estimate of livestock methane. We wonder if the FAO’s estimate of non-livestock methane is any more reliable. One wonders why, in fact, the original LCC article did not make this problem, rather than the different method of accounting for methane, more of an issue.

Goodland points out that, since LCC was published, it turns out that there are even more livestock than we thought. The FAO report put the number of livestock at 21.7 billion, LCC put it at nearly 50 billion, but new figures from the FAO itself now put it at 56 billion, 258% higher than the figure used in Livestock’s Long Shadow and 10% higher even than the higher estimate in LCC. Goodland comments: "This is many more than are counted in our article, and doubtless outweighs whatever the increase would be in non-livestock methane."

Walsh’s basic point that we need to recalibrate both livestock and non-livestock methane emissions is correct, but does not invalidate the general conclusions of LCC.