Rows of corn grow near an unplanted field outside Wyanet, Ill., on Tuesday, May 28, 2013. (Daniel Acker/Bloomberg)

When we talk about why the planet is warming, we talk about fossil fuels — oil, gas, coal and their many variants. What we rarely say or think to say, though, is that’s not the whole story.

The fact is that plants take in carbon dioxide in the process of photosynthesis, and release it again when they die. So if you clear large swaths of land, so that it does not contain as many trees, crops, or grasses as before, then you are also contributing to global warming. The same goes for other agriculture related emissions, ranging from nitrous oxide emissions from the use of fertilizers to methane emissions from “enteric fermentation” in cattle (those infamous  “cow farts” — although really, it’s mainly cow burps).

No wonder there have been complaints over the years about U.S. agriculture “getting a pass,” or land-use changes being “largely ignored,” when it comes to greenhouse gas emissions and climate policy. It’s in this context that a new move by the Department of Agriculture to slash the sector’s emissions markedly by the year 2025 — and to do so simply through voluntary measures  — is so significant.

“It’s roughly the amount of emissions that would be generated from the energy use of 11 million homes on an annual basis,” said Agriculture Secretary Tom Vilsack, who is slated to unveil the plans at Michigan State University on Thursday.

The expected reductions would come from curtailing agricultural emissions, increasing the ability of lands to store or sequester carbon, and also increasing renewable energy use in rural areas and energy efficiency in farming. If achieved, the net effect would help the United States reach its intended goal of slashing total emissions by 26 to 28 percent below 2005 levels by the year 2025, a target announced in the fall in a historic agreement with China.

The new policy will include 10 “building blocks” which the Agriculture Department says will cut more than 120 million metric tons of carbon dioxide equivalent annually by 2025. The broad suite of policies includes targeting livestock related emissions — by increasing anaerobic digestion, making sure there are roofs to contain some methane emissions, and also changing grazing habits so as to preserve more carbon in soils — the reforestation of fire or pest-damaged areas, and much more.

Most intriguing, perhaps, is a program to use damaged trees from those same kinds of disasters to construct buildings, thereby storing the wood’s carbon (which would otherwise be released back into the atmosphere when the tree decomposes).

“We’re basically treating them, putting them into a building,” said Vilsack. “That will restore and retain that carbon storage, but also, as a building material, has less emissions than cement or steel.”

The Agriculture Department also said it is using the federal crop insurance program to bring about emissions reductions, since farmers have to fill out several forms about conservation practices to be able to receive such insurance, and that it will work to increase renewable energy and energy efficiency on farms and in rural areas.

How significant would the changes be? Recently, the EPA released new figures on the U.S.’s total 2013 greenhouse gas emissions, noting that net emissions — including all sources, but also subtracting sinks where carbon is stored, such as forests — totaled 5791.2 million metric tons of carbon dioxide equivalents. Total agricultural emissions in 2013, EPA added, were 515.7 million metric tons.

Thus, the Agriculture Department said, agricultural emissions are about 9 percent of the U.S. total, and the new policy — a net reduction of 120 million metric tons — would be equivalent to a more than 20 percent cut. (Granted, the reduction does not solely come from agricultural emission reductions, since it also includes new carbon storage in forests and lands, and changes in energy use.)

“This is a very innovative and creative effort to look across all of the programs and tools that USDA has, and find voluntary and incentive based programs where you can help increase the bottom line of farmers and ranchers and others in the sectors, while at the same time mitigating carbon emissions,” said Brian Deese, a senior White house adviser focused on climate and energy policy.

It is also voluntary, not mandatory. Many of the new steps, said Vilsack and Deese, draw on existing powers in the 2014 Farm Bill to either help or incentivize farmers and landowners to adopt different practices. In many cases, Vilsack asserted, farmers will actually benefit from the new programs.

“The critical message here is that conservation, focusing on reducing greenhouse gases, doesn’t have to cost you, it can actually be something that in the long run you profit from,” said Vilsack.

After the historic climate agreement with China — and more recently, after the State Department submitted, to the United Nations, its “intended nationally determined contribution” detailing how the United States plans to cut greenhouse emissions to meet its targets — some critics pounced, saying the numbers just didn’t add up.

The U.S. Chamber of Commerce, for instance, has questioned how the United States will meet the targets announced in the China deal, saying that “about 40% of necessary reductions” are “still unidentified.” And in a blog post last week, the heads of Element4 Consulting, former Sierra Club chief counsel David Bookbinder and former ExxonMobil climate policy manager David Bailey, questioned President Obama’s “Dubious Climate Promises.”

Bookbinder and Bailey suggested, through a series of estimates, that the United States could not meet its intended 2025 target based on the programs currently outlined, such as the EPA’s Clean Power Plan. There were, in their analysis, about 330 million metric tons of carbon dioxide equivalent per year left to cut.

Adding in the newly announced agricultural emissions cuts would reduce that by over a third.