The case for geoengineering begins with the recognition that the most widely discussed “solutions” to global warming—such as riding a bike rather than driving a car and making electricity from wind rather than natural gas—address only the 2 ppm part of the problem while leaving the 400 ppm part untouched. To be sure, reducing the 2 ppm of annual emissions growth is absolutely necessary—it just doesn’t go far enough. At 400 ppm, global warming is already contributing to a mounting litany of record-breaking weather. In the last year, the United States alone has suffered its hottest summer on record, its worst drought in 50 years, and the largest Atlantic hurricane on record, Superstorm Sandy. Globally, the list of climate-related extreme weather events is much longer.
What’s more, even if annual emissions of greenhouse gases drop to zero, global temperatures will keep rising and climate impacts keep intensifying for decades to come, thanks to the inertia of the climate system. The only way to possibly reduce impacts in the years ahead is to address what is fundamentally driving them: the 400 ppm of CO2 currently in the atmosphere.
According to Pollan, photosynthesis is “the best geoengineering method we have.” It’s also a markedly different method than most of the geoengineering schemes thus far under discussion—like erecting giant mirrors in space or spraying vast amounts of aerosols into the stratosphere to block the sun’s energy from reaching Earth. Whether any of these sci-fi ideas would actually work is, to put it mildly, uncertain—not to mention the potential detrimental effects they could have.
By contrast, we are sure that photosynthesis works. Indeed, it’s only a slight exaggeration to say that photosynthesis is a major reason we humans can survive on this planet: Plants inhale CO2 and turn it into food for us, even as they exhale the oxygen we need to breathe.
What does all this have to do with eating meat? Here’s where Pollan gets positively excited. “Most of the sequestering takes place underground,” he begins.
“When you have a grassland, the plants living there convert the sun’s energy into leaf and root in roughly equal amounts. When the ruminant [e.g., a cow] comes along and grazes that grassland, it trims the height of the grass from, say, 3 feet tall to 3 inches tall. The plant responds to this change by seeking a new equilibrium: it kills off an amount of root mass equal to the amount of leaf and stem lost to grazing. The [discarded] root mass is then set upon by the nematodes, earthworms and other underground organisms, and they turn the carbon in the roots into soil. This is how all of the soil on earth has been created: from the bottom up, not the top down.”
The upshot, both for global climate policy and individual dietary choices, is that meat eating carries a big carbon footprint only when the meat comes from industrial agriculture. “If you’re eating grassland meat,” Pollan says, “your carbon footprint is light and possibly even negative.”
Some, but not all, of Pollan’s analysis here resembles the holistic management of grasslands advocated by Allan Savory, a biologist from Zimbabwe whose TED talk earlier this year provoked widespread interest. Savory has his critics, though, including James McWilliams, a historian at Texas State University, who wrote in Slate that the most comprehensive scholarly analyses of holistic grazing found that it did not improve plant growth or, by implication, carbon sequestration. Savory and his allies argue that the studies cited by McWilliams did not follow his prescribed methods of holistic management and thus prove nothing about it.
For his part, Pollan emphasizes that switching from corn-fed to properly grazed cows brings other benefits as well. Sequestering carbon improves the soil’s fertility and water retentiveness, thus raising food yields and resilience to drought and floods alike. Says Pollan: “I’m a believer in geoengineering of a very specific kind: when it is based on bio-mimicry”—that is, it imitates nature—“rather than high-tech interventions and when instead of being a silver bullet solution it solves multiple problems—in this case, climate change and soil quality and food security.”
Pollan calls this approach “open source carbon sequestration.” He emphasizes that more research is needed to understand how best to apply it, but he is bullish on the prospects. Using photosynthesis and reformed grazing practices to extract atmospheric carbon and store it underground “gets us out of one of the worst aspects of environmental thinking—the zero sum idea that we can’t feed ourselves and save the planet at the same time,” says Pollan. “It also raises our spirits about the challenges ahead, which is not a small thing.”