Creque had an answer for him. The carbohydrates that fattened the cows had come from the atmosphere, by way of the grass they ate. Grasses, he liked to say, were like straws sipping carbon from the air, bringing it back to earth. Creque’s quiet observation stuck with Wick and Rathmann. It clearly illustrated a concept that Creque had repeatedly tried to explain to them: Carbon, the building block of life, was constantly flowing from atmosphere to plants into animals and then back into the atmosphere. And it hinted at something that Wick and Rathmann had yet to consider: Plants could be deliberately used to pull carbon out of the sky.

Climate change often evokes images of smokestacks, and for good reason: The single largest source of carbon emissions related to human activity is heat and power generation, which accounts for about one-quarter of the carbon we put into the atmosphere. Often overlooked, though, is how we use land, which contributes almost as much. The erosion and degradation of soil caused by plowing, intense grazing and clear-cutting has played a significant role in the atmospheric accumulation of heat-trapping gases. The process is an ancient one. Ice cores from Greenland, which contain air samples trapped thousands of years ago, reveal increases in greenhouse gases that correspond with the rise of farming in Mesopotamia.

Since the start of the Industrial Revolution, agricultural practices and animal husbandry have released an estimated 135 gigatons — 135 billion metric tons — of carbon into the atmosphere, according to Rattan Lal, a soil scientist at Ohio State University. Even at current rates, that’s more than a decade’s worth of carbon dioxide emissions from all human sources. The world is warming not only because fossil fuels are being burned, but also because soils, forests and wetlands are being ravaged.

In recent years, some scientists have begun to ask whether we can put some of that carbon back into the soil and into living ecosystems, like grasslands and forests. This notion, known as carbon farming, has gained traction as it becomes clear that simply reducing emissions will not sufficiently limit global warming. According to the 2014 report by the Intergovernmental Panel on Climate Change, an authority on climate science that operates under the auspices of the United Nations, humankind also needs to remove some of the carbon already in the atmosphere to avoid, say, the collapse of polar glaciers and the inundation of coastal cities worldwide. “We can’t just reduce emissions,” Keith Paustian, a soil scientist at Colorado State University and an author of an earlier I.P.C.C. report, told me. “It’s all hands on deck. Things like soil and land use — everything is important.”

Some of the proposed methods to begin this drawdown include scrubbing the air with great air-conditioner-like machines; fertilizing the oceans with iron dust to prompt algal blooms that, when they die, carry captured carbon to the bottom of the sea; capturing and storing the carbon dioxide that results when energy is produced by burning trees and other plants that removed carbon from the atmosphere during their growth; and crushing and spreading certain types of rock, like basalt, that naturally absorb atmospheric carbon. None of these approaches are yet proved or affordable at the scale needed to make a difference. The most obvious hurdle is the additional energy some of them require, which, unless it comes from a free, renewable source, adds more costs.

Plants, however, remove carbon from the atmosphere already, require no additional power and grow essentially free. During photosynthesis they harness the sun’s energy to make sugars by combining hydrogen atoms (acquired from water molecules) with carbon atoms (from carbon dioxide), while emitting oxygen as a byproduct. (Lest we forget, the fossil fuels that now power civilization contain carbon removed from the air during photosynthesis millions of years ago.) Every spring, as the Northern Hemisphere greens, the concentration of carbon dioxide in the atmosphere dips, before rising again the following fall and winter as foliage dies. Some scientists describe this fluctuation as the earth breathing.

Nearly all the carbon that enters the biosphere is captured during photosynthesis, and as it moves through life’s web, every organism takes a cut for its own energy needs, releasing carbon dioxide as exhaust. This circular voyage is the short-term carbon cycle. Carbon farming seeks to interfere with this cycle, slowing the release of carbon back into the atmosphere. The practice is often conceptualized and discussed in terms of storing carbon, but really the idea is to change the flow of carbon so that, for a time at least, the carbon leaving a given ecosystem is less than the carbon entering it.