23.

You Will Grow a Carbon Farm

Why compost and cows may be the next big things in climate science.

By Karen Leibowitz

Most people think of burning fossil fuels as the main culprit when it comes to climate change, but in fact, agriculture accounts for about 30 percent of greenhouse gas emissions worldwide. Farming has been a source of greenhouse gases since its invention, about 10,000 years ago, when we began converting forests into farmland and plowing the soil, releasing carbon dioxide into the air. Soon, though, we’ll have the opportunity to turn agriculture into part of the solution. After several years of experimenting, scientists and farmers have found that a concerted campaign of “carbon farming” — the practice of converting carbon dioxide from the atmosphere into plant material and soil matter — can dramatically reduce emissions and revolutionize the way we farm.

Here’s how it works:

Illustration by Jessica HJ. Lee

As a plant grows, it takes in carbon dioxide (CO2) from the air and breaks it into carbon (C), which builds cells, and oxygen (O2), which is released as a waste product. Trees and deep-rooted plants like perennial grasses store more carbon than shallow plants because their longer roots are surrounded by a nutrient-rich region of soil where microorganisms convert CO2 into organic matter in a process called soil carbon sequestration. We can jump-start this process by spreading grasslands with a layer of compost, which seeds the soil with good microorganisms, resulting in more soil carbon sequestration.

Herd animals like cattle and sheep contribute their own manure (along with some microorganisms) to the soil, while their hooves push the manure and compost into the earth, promoting soil carbon sequestration. Moving livestock from one field to another in tight groups, so that each field is grazed intensively and allowed to recover, further encourages the growth of deep perennial roots. And the plants that are trimmed through grazing will shed some roots below the surface, becoming fodder for bacteria to accomplish even more soil carbon sequestration.

Scientists and ranchers with the Marin Carbon Project have found that if half of California’s unused grassland were converted to carbon farming, it would offset all of the carbon dioxide emissions from energy use in the whole state. In an era of dire warnings from climate science, the idea of carbon farming offers an optimistic breath of fresh air to herald in 2015.

Karen Leibowitz is a writer, editor, and the co-founder of Mission Street Food.