Humans are cultivating almost 40 percent of the land surface of the earth, and nearly a third of all the greenhouse gas emissions that are warming the planet comes from agriculture and forestry. Those emissions are linked not only to the factors that many people tend to think about, like the fossil fuels burned in transporting food; that, in fact, is only a minor source of emissions.
Nitrogen fertilizer, though essential to producing food for seven billion people, is one large source of emissions, and not only because it requires natural gas to produce. After it is spread on farmers’ fields, a portion of it turns into a potent greenhouse gas that escapes into the atmosphere. (As many people know, some nitrogen also washes into rivers and streams, ultimately making its way to the ocean, where it contributes to dead zones at the mouths of many of our great rivers, including the Mississippi.)
The biggest of all the ways that agriculture contributes to climate change, though, is the chopping down of forests to make way for farms and cattle grazing. The world’s forests are enormous stores of carbon dioxide, and when they are cleared, the vegetation that is burned or allowed to decay oxidizes into carbon dioxide, the major greenhouse gas. In recent years, changes in land use have accounted for some 25 percent of the carbon dioxide being emitted on the planet, and the bulk of those changes are driven by agriculture.
As my colleague Elisabeth Rosenthal has reported here and here, efforts are under way to slow deforestation. But scientists say that alone will not be enough. Somehow, even as humanity increases the production of food over the coming decades, it must reduce the environmental footprint of agriculture. The alternative is continued ecological degradation and a worsening of climate change, which in turn would make food production harder.
When you view the problem in that light, the challenge of feeding ourselves becomes that much larger.