A coalition of environmental, agriculture and justice groups is attempting to drum up opposition to legislation that aims to help farmers store carbon in the soil, a practice that’s become a key piece of the Biden administration’s strategy on climate change.

In a letter sent to members of Congress this week, the groups urge lawmakers to vote against the Growing Climate Solutions Act, a bill first introduced last year that would help create a voluntary carbon market, in which polluting companies would offset their emissions by paying farmers to conserve soil in ways that store carbon or to take measures to reduce emissions on their farms.

The concept has become politically popular, gaining favor with both Democrats and Republicans, even those skeptical of the science on climate change. Then-candidate Joe Biden discussed soil carbon on the campaign trail and vowed to make American agriculture reach net-zero emissions. His administration has called agriculture “a linchpin” in its plan to tackle climate change.

The reduction of emissions from agriculture is likely to be a component of the United State’s pledge to reduce overall emissions under the Paris climate agreement, which will be unveiled next week.

Soil has the potential, in theory, to trap carbon in the soil, keeping it out of the atmosphere where it contributes to warming. If farmers employ certain practices—for example, avoiding  tilling the soil, planting carbon-fixing crops or using feed additives that reduce methane emissions from cows—they can help keep carbon in the soil, or cut the emission they produce. These practices would generate a “credit” that a company like a utility could buy to offset its own polluting emissions.

Over the past two years, support for creating such a market has gained traction even with the powerful farm lobby, which has derailed previous attempts to create carbon markets and continues to question the science on climate change. As recently as last year, members of the American Farm Bureau Federation voted to embed  climate change skepticism in its annual policy documents.

But especially with an ailing farm economy, battered by a series of weather events, the global Covid-19 pandemic and former President Donald Trump’s trade war with China, the idea of giving farmers another revenue stream has taken off.

Opponents have also started to emerge, in part motivated by the unlikely groups that have come together to support the idea of carbon markets. 

“The Farm Bureau and its members just want to get paid,” said Steve Suppan of the Institute for Agricultural Trade Policy, one of the organizations that sent the letter this week. “They don’t want to be obliged to do anything, so now you have a set-up where they’re taking taxpayer money again.”

In the letter, the nearly 200 groups, which include the environmental advocacy groups Greenpeace, the Center for Biological Diversity and Friends of the Earth as well as Public Justice, the Center for Food Safety and the Organic Consumers Association, point out their broader opposition to carbon markets. 

“These carbon offset schemes allow utilities, fossil fuel companies and other polluters to continue releasing greenhouse gases, instead of actually reducing and eliminating their emissions,” the groups said. “This is because fossil fuel-based carbon extracted from where it has been sequestered underground for millions of years, safely trapped in the slow carbon cycle, cannot be offset by temporary actions in the short carbon cycle.”

Most of Earth’s carbon is locked in “slow exchange” geological formations as fossil fuels, the groups explained, and can take millions of years to cycle into the atmosphere, unless it’s suddenly disturbed by fossil fuel extraction or volcanic activity.  Soil and forests, on the other hand, are “fast-exchange” reservoirs of carbon that can re-release carbon within decades or even more quickly, from land conversion.  “The Earth is not an endless sponge to absorb fossil fuel carbon,” the letter said. “If it was, we would not have climate change.”

The opponents say that the Growing Climate Solutions Act would “pave the way” for a national cap-and-trade program, something they oppose because the carbon pollution that is offset with these types of programs often ends up in poorer and minority communities.

“It is no wonder why these different groups are coming together when you consider offset scams like those promoted in the Growing Climate Solutions Act are increasing pollution in environmental justice communities, while undermining efforts to build a more sustainable system of agriculture and address the climate crisis,” said Jim Walsh, senior energy policy analyst with Food & Water Watch, one of the groups that sent the letter.

Under the Growing Climate Solutions Act, the U.S. Department of Agriculture would set up a carbon bank that would help pay farmers for carbon credits or support prices. (It’s not entirely clear how the bank would operate and the department is currently taking comments from farmers as it develops the program.)  

The Agriculture Department would also establish guidelines for verifying and accounting for emissions reductions, although the verification would be conducted by outside parties.

The groups that signed onto this week’s letter echoed earlier concerns, by both advocacy groups and scientific researchers, that techniques for measuring soil carbon and soil’s long-term capacity to store carbon are imperfect. 

“Methods for measuring soil carbon sequestration remain underdeveloped, inconsistent, and influenced by specific climates and geographies,” they say. “There is simply no way to accurately estimate carbon sequestration because the fast carbon cycle does not function this way.”

Groups in favor of the bill, or the broader idea of carbon markets, point to research that demonstrates the huge potential of soil to sequester carbon. Some of the country’s top soil scientists have long supported the idea and have stressed the urgency of controlling emissions on a scale of decades

“For many of these groups the core agenda is not climate change but transforming how agriculture is performed here in the U.S.,” said Ernie Shea, president of Solutions From The Land, a collaboration of conservation and agriculture industry organizations, referring to this week’s letter. “Like often in politically charged debates, the quest for the perfect becomes the enemy of the good. Sadly this appears to be the case here.”

The legislation was introduced in the House by Rep. Abigail Spanberger, a Virginia Democrat, originally with a bipartisan group of nine representatives as co-sponsors. The Senate version of the bill was introduced by Indiana Republican Mike Braun, originally with three Senators, including Democrats Debbie Stabenow of Michigan, Sheldon Whitehouse of Rhode Island and Republican Lindsey Graham of South Carolina as co-sponsors.