Here it is:
A report from Science News(via Food Times) argues that beef produces 19 kilograms of CO2 for every kilogram served; that grass-fed beef is worse — yes, worse — for global warming than feed-lot beef; and that for every percentage reduction we make in meat consumption we’ll see a corresponding reduction in its contribution to global warming.
(Also repeated at the Times' Dot Earth.)
If you click the link, as we all should, you get the problem: “We do see significant differences in the GHG intensities [of grass vs grain finishing]. It’s roughly on the order of 50 percent higher in grass-finished systems.”
So what's the difference between grass-raised versus grass-finished? I see it here in Santa Clara County in my work attempting to protect open space. We have hundreds of thousands of acres of hillside ranchlands primarily used for cattle raising, based on grass. Finishing is what happens last, when cattle are taken to feedlots to fatten up before slaughter.
Back to the Science News article:
When an audience member questioned whether he had heard that right, that grass-fed cattle have a higher carbon footprint, Pelletier reiterated, “higher. Yes.” The reason: “It’s related to the much higher volumes of feed throughput and associated methane and nitrous-oxide [GHG] emissions.” He added that most pastures were highly managed, and subject to “periodic renovations and also fertilization.”
The use of "grass-fed" is from the article, not Pelletier, and I think it's a mistake. So is everything else in that quote at least as it applies here. Almost none of the ranchlands in my county are fertilized or irrigated, and I expect the same is true for most of California for non-dairy cattle.
The only realistic food use of relatively dry hillsides here, and I suspect in much of the world, is grazing animal production. The alternative is intensive agriculture somewhere else, and I think that's been missed in the climate analysis.
I don't think this issue is completely resolved - finishing cattle, much of which may be unnecessary, can cause problems, and there's the methane production issue that I don't completely understand, but I'm sure the simple conclusion the Times reached hasn't been proven.
(Disclosure: I sometimes eat beef or buffalo, and try to get grass-fed.)