In Michael Grunwald’s new fantastic book, We Are Eating the Earth, he points out that “since World War II, the U.S. dairy herd has shrunk by two-thirds.” It’s true–in 1944, there were 25.6 million dairy cows and now there are 9.3 million. This is even more striking when you consider that in 1944 there were 138 million Americans and now there are 342 million.

How can this be? Is it because rates of lactose intolerance are rising, or because people started to realize that dairy is a land-intensive process that’s bad for the climate? Or is it a triumph of vegan advocacy that convinced people to consume less milk, and instead drink alternatives like soy, oat, and almond milk?

None of the above–it’s because the average output of a dairy cow increased from 4,572 lbs per cow to 24,178 lbs per cow. That increase came from decades of selective breeding, improved nutrition, better veterinary care, and more optimized farm management. When each cow produces five times as much milk, you need significantly fewer of them

Getting more with less is a central theme in We Are Eating the Earth, where Grunwald offers a sober, realistic, and insightful take on how we can feed a growing population in a world that’s heating up faster than we’d like. He zeroes in on how we tally the climate costs of agriculture, and how bad climate accounting has led us toward flashy but counterproductive solutions. When we do the accounting right, two truths emerge: first, there are no silver bullets in agriculture. Second, increasing productivity is one of our most powerful tools, because it lets us produce more food with less impact.

Focusing on the virtues of agricultural productivity may seem surprising coming from a staunch environmentalist like Grunwald. But it reflects a broader truth: industrial agriculture may cause emissions, pollution, and poor animal welfare, but the more efficient agriculture is, the less of it we need.

The Opportunity Cost of Land

When it comes to climate accounting, Grunwald argues that land use is often the most overlooked aspect. The reason conserving land is important isn’t just to preserve scenic vistas or to protect endangered species. It’s because forests, grasslands, and other natural ecosystems are the best ways we have to keep carbon in the ground rather than in the atmosphere. Converting land to other uses, even purportedly climate-friendly ones, always comes with ...