A public accounting of the greenhouse gases that will be emitted by a proposed dairy expansion west of Winona highlights a new level of attention in Minnesota to the climate-change impact of cows.

The Minnesota Pollution Control Agency (MPCA) said this week that the Lewiston, Minn., dairy Daley Farms, if it expands by a planned 3,000 cows, will generate about the equivalent of 32,500 tons of carbon dioxide per year.

That's more than the greenhouse gas emissions from 6,000 cars in a typical year, most of it coming in the form of methane, a gas that vents into the atmosphere from manure lagoons and from the cows themselves.

The estimate was ordered by the Minnesota Court of Appeals, which in October revoked a permit for Daley Farms to expand, saying state-pollution regulators had failed to consider greenhouse gas emissions in their environmental review of the project.

The MPCA said it will now disclose greenhouse gas emissions estimates for all future feedlot projects requiring environmental review, something it already does for energy and ethanol projects.

Dairies are coming under the microscope because the industry is undergoing rapid consolidation, creating greater concentrations of cows and consequently methane, a byproduct of cow digestion that is a highly potent greenhouse gas.

While not as persistent in the atmosphere as carbon dioxide, methane has 25 times the global warming potential of CO2 over the span of 100 years.

The Daley expansion would bring the dairy's total number of cows to 4,628 — making it one of the largest in the state. But dairy-industry consolidation doesn't pencil out to more emission of greenhouse gases in Minnesota.

The state lost 315 dairies in 2019, including 47 in December alone. Despite the expansions of large dairies, the overall number of milk cows in Minnesota is steadily declining. There are 10,000 fewer cows at dairies in the state — 446,000 — than there were two years ago.

It's also not at all clear that mega-dairies produce more greenhouse gas per cow than small dairies.

"It's highly variable," said Melissa Kuskie, manager of the MPCA environmental review program. "There's no definitive answer, though I do think that the way cows are managed has an effect on emissions."

Regardless, projects such as the Daley Farms proposal have drawn vigorous opposition.

Environmental groups raised concerns about the expansion's effect on drinking water in the area. The Minnesota Center on Environmental Advocacy and the Land Stewardship Project filed suit against the MPCA's decision to issue a permit a year ago.

That case resulted in the Court of Appeals ruling that the MPCA must estimate the project's greenhouse gas emissions.

Katrina Kessler, an assistant commissioner at the MPCA, said the estimate for the Daley proposal is part of a broader effort to track greenhouse gas emissions across the state and help policymakers and industry work toward cutting emissions over time.

It does not, however, signal one way or the other about the expansion permit's ultimate approval.

"It's not meant to be compared to any threshold," Kessler said.

A draft of the Daley Farms permit and environmental review are available on the MPCA's website. The agency is taking public comments until Feb. 20 and will issue a decision on the permit within 30 business days after that.

A public meeting will be at 6:30 p.m. Feb. 4 at the Lewiston Community Center in Lewiston, Minn.

Ben Daley, one of the farm's owners, said he would be surprised if the permits aren't ultimately approved, but he also "didn't think we were going to get dragged into greenhouse gases" when his family proposed the expansion.

"We're very hopeful, and we want to do it," Daley said. "We've got a dozen family members working on that farm, and that's what it's about, the next generation. It's not just one farmer trying to grab all he can."

Adam Belz • 612-673-4405 Twitter: @adambelz