Carbon as a Tool, Soil as a Sink

In November 2016, the American designer and author William McDonough (of Cradle to Cradle renown) published a short essay titled “A New Language for Carbon” in the journal Nature. In the opening few sentences, McDonough lays out his main idea in clear terms: “Anthropogenic greenhouse gases in the atmosphere make airborne carbon a material in the wrong place, at the wrong dose and wrong duration . . . In the right place, carbon is a resource and tool.”

The timing of the essay was not a coincidence. COP22 would meet that month in Morocco—it was the first convening of signatories since the 2015 Paris Climate Agreement. McDonough’s essay speaks indirectly to one of the more controversial assumptions embedded in the underlying math of the Agreement’s goal and timeframe: emissions reductions are no longer sufficient to prevent climate catastrophe, and negative emissions applications (which reduce carbon and other GHG concentrations in the atmosphere) must be rapidly scaled in the coming decades.

But where exactly is “the right place” to put civilization’s excess carbon so that the goals of Paris are fulfilled or exceeded, and how do we put it there? How can the gigatons of GHGs we’ve already produced be repurposed from “time bomb,” as the scientific community in near unison grimly warns, into “tool,” as McDonough appeals?

One place that’s nearly as ancient as the carbon cycle itself and which is practically begging for more carbon is right beneath our feet: soil. As an earth feature, collectively referred to as the pedosphere, it is the largest terrestrial reservoir of global carbon, holding more than the atmosphere and all of the planet’s surface vegetation combined. And it can hold more. A lot more.

However, rather than acting as a sink, today the pedosphere is a net source of atmospheric carbon. This is the result of disruptive agricultural methods and land use changes that humans have used for millennia, but which have vastly expanded and accelerated since the beginning of the industrial era. This loss of soil carbon is inflicting two separate blows by adding to atmospheric carbon (and therefore driving climate change) on one hand, while diminishing soil resilience and productivity on the other. In an increasingly hot planet with 8 billion people to feed, we cannot afford to let this trend continue. Carbon needs to go back into the soil, and there are proven ways of doing this—in the agricultural context this includes no-till farming, cover crop farming and managed grazing.

But what about soil in the urban built environment? What might be the local and global benefits of increasing soil carbon in places like New York City, and is it even possible to do so? Exploring these very questions will be the aim of the panel discussion that I will be moderating on June 2, Capturing Carbon in Urban Soil: What’s Possible in Cities.

I will be joined by microbial biologist Peter Groffman, soil scientist Sara Perl Egendorf and sustainable horticulturist Eric T. Fleisher. The panel will discuss the underlying science of soil carbon; the potential, limitations and possible benefits of urban soil sequestration; and emerging approaches in soil management—some of which are being used right here in New York.

About the authors

Chris Neidl
Christopher Neidl is a clean energy policy advocate, educator and project advisor with thirteen years of experience facilitating on-grid and off-grid clean energy adoption in the United States, Asia and Africa.