MILLVILLE -- An innovative program that allows farmers who employ conservation practices to sell "carbon credits" through the Chicago Climate Exchange has been opened up to farmers in almost all of Pennsylvania, the president of the Pennsylvania Farmers Union said Friday.

Carbon dioxide is one of six greenhouse gases, the emissions of which trap heat in the atmosphere, contributing to global warming.

The climate exchange is a financial institution whose members, typically businesses whose operations produce greenhouse gases, agree to cut their emissions by a certain amount.

If they are falling short of their pollution-reduction goals, then they can buy the carbon credits from others trading on the exchange, like the farmers, said Larry Breech, the farmers union president.

"This is a program that pays farmers for doing what they're doing anyway," said Mr. Breech, a Millville farmer.

Selling the carbon credits through the climate exchange is one that would be difficult, if not impossible, for most farmers, but the Farmers Union set up a program to serve as an "aggregator" so that lots of farmers can sign on together and as one group, they can exchange their carbon credits and split the proceeds, Mr. Breech said.

"This allows anyone to play," he said.

Information from the climate exchange suggests that the going rate for carbon credits is about $3.50 per ton.

A map on the National Farmers Union Web site suggests that Pennsylvania farmers would get credit for 0.6 tons of carbon emissions per acre for using no-till farming practice.

Farmers can also get credits for having seeded grass and forage stands. Those practices earned carbon credits at a rate of 1 ton per acre. Other practices, such as having a manure digester that captures methane gas instead of allowing it to be released into the atmosphere, offer more carbon credits. Each ton of methane captured earns 18 tons of carbon credits.

For serving as the aggregator, the Farmers Union takes a 10 percent fee. The Farmers Union got involved in the carbon credits through the North Dakota office of the organization.

The carbon credit program was just expanded to include Pennsylvania, Mr. Breech said.

The businesses that buy the carbon credits often are doing so to compensate for pollution being produced at their overseas facilities, Mr. Breech said.

The carbon credits can be sold by the person who does the farming instead of by the landowner, if they are not the same person, he said.

"It's like the lottery, you have to be in to win," Mr. Breech said.