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.'”