WASHINGTON — Potential impacts the Environmental Protection Agency’s recent greenhouse gas (G.H.G.) ruling could have on agriculture operations has the National Cattlemen’s Beef Association "extremely concerned." E.P.A.’s decision, announced Dec. 7, claims G.H.G. emissions are an endangerment to public health and the environment.

This sets the stage for G.H.G. regulation under the Clean Air Act (C.A.A.) and would give the E.P.A. unprecedented control over every sector of the U.S. economy, N.C.B.A. said.

It’s premature to issue this kind of finding, especially given the recent controversy surrounding the scientific validity of alleged human contributions to climate change, said Tamara Thies, N.C.B.A. chief environmental counsel. "Regulation of greenhouse gases should be based on science, and it should be thoughtfully considered and voted on by Congress through a democratic process, not dictated by the E.P.A.," she added.

She added the endangerment finding does not itself regulate G.H.G.s; but unless Congress acts, it sets in motion E.P.A. regulation of G.H.G.s from stationary sources and setting new source performance standards for G.H.G.s.

On Oct. 27, E.P.A. proposed a rule designed to regulate G.H.G. emissions from sources that emit 25,000 tons per year or more, instead of the statutory 250 tons per year threshold for pollutants, which is included in the Clean Air Act. To what extent E.P.A. can change statutory permitting requirements, however, remains unclear. Only time will tell how federal courts will address citizen suits to force regulation of all sources that emit G.H.G.s in excess of the statutory thresholds, Ms. Thies said.

E.P.A. indicated it would also develop an approach to regulate G.H.G.s from hundreds of thousands of small operations, including farms and buildings.

While agricultural sources are currently generally not required to obtain permits for greenhouse gas emissions, regulation of G.H.G.s under the C.A.A. may for the first time trigger such regulation, Ms. Thies said. Seeing that the U.S. currently has more than 2 million farms, it would be impossible to permit most of them. It would also impose massive regulatory compliance costs on producers, which could force many operations out of business, she added.

"Congress never intended for the Clean Air Act to be used for greenhouse gas regulation," Ms. Thies said. "While the Act has done a good job of cleaning up pollutants, it is not adequately equipped to address global climate change. Any attempts to use it for this purpose would be devastating to U.S. agriculture."

In 2007, G.H.G. emissions from the entire agriculture sector represented less than 6% of total U.S. G.H.G. emissions in Tg CO2 Eq, according to the E.P.A. At the same time, land use, land use change and forestry activities resulted in a net carbon soil sequestration of approximately 17.4% of total U.S. CO2 emissions, or 14.9% of total U.S. greenhouse gas emissions.

"Agriculture actually provides a significant net benefit to the climate change equation," Ms. Thies said. "Rather than being subject to overly-burdensome regulations, agriculture should be rewarded for the carbon reductions we provide."