The 2,700 pigs on the farm of Sterksel, the Netherlands, that John Horrevorts manages, yield more than ham and bacon. A biogas plant makes enough electricity from their waste to run the farm and feeds extra wattage into the Dutch national grid.

He even gets bonus payments for reducing greenhouse gas emissions.

As the world struggles to reduce pollution causing climate change, attention has focused on the burning of fossil fuels in factories, power stations and vehicles. But United Nations scientists say farming and forestry account for more than 30 percent of the greenhouse gases that are gradually heating the earth. Much of that pollution comes from cattle, sheep and pigs that belch or excrete methane, a heat-trapping gas more than 20 times as potent as carbon dioxide, the most common global warming gas.

Negotiators from 190 countries have been working to reach a new climate change agreement on ways to reduce emissions and help countries adapt to changes in climate. They reconvened this week in Bonn, Germany, for another two-week session.

Yet it is uncertain whether cutting agricultural emissions will be part of the agreement expected to emerge at the final meetings in Copenhagen, Denmark. The subject is complex, emissions are difficult to measure, and the whole question is politically sensitive, touching on the distrust between the world's rich and poor countries.

Scientists say it is too important to be left out.

"It would be absolutely nuts to ignore agriculture and forestry in any future climate deal," said Pete Smith, professor of soils and global change at the University of Aberdeen in Scotland.

UN studies say agriculture is the main source of income for one of every three working people. It also is a growing source of pollution, as populations and living standards rise in developing countries where meat is eaten more often.

The latest research by the UN's Food and Agriculture Organization says animal husbandry accounts for 18 percent of all greenhouse gases, when taking into account the grassland and forests that are cleared for raising livestock.

One way to deal with methane is to reduce the amount animals produce by changing their diet or via breeding. Another is to make use of it and burn it.

Horrevorts says Wageningen University's Praktijkcentrum, or Sterksel Research Center, creates 5,000 megawatts a year, enough to power 1,500 homes. The farm uses the electricity it needs and feeds the rest into the national grid, for which the government pays up to 177 euros (US$238) per megawatt as a green energy subsidy.

Pigs can be remarkably house-broken animals. Here, they drop their waste through slats on the floor in the middle of the barn while spending most of their time in open stalls to the side. The slurry is channeled into three 4,000-cubic-meter tanks, then mixed into a thick goo with other organic waste like low-quality grain and carrot juice to increase the methane potential. Bacteria break down the material in a digester tank and the gas is siphoned off into a generator to produce electricity.

Horrevorts says a group including his operation and four other commercial farms avoids methane emissions equivalent to 40,000 tons of carbon a year. Dozens of private or non-profit companies known as offset providers will "buy" those tons as a way of supporting renewable energy or other projects that reduce carbon emissions, then resell the credits to individuals or companies who want to shrink their carbon footprint.

Though operating expenses for the biogas plant are high, the mix of electricity savings, power production and carbon credits makes it profitable, Horrevorts says.

But at 1 million euros for a plant like Sterksel's, it's a rich answer to climate change.

About 70 percent of the world's agriculture is on small land holdings in the developing world, which complicates climate politics, says Antonio Hill of the nonprofit group Oxfam International.

In the past year, much effort has gone into quantifying emissions from deforestation in the tropics and ways to compensate countries like Brazil or Indonesia for protecting their rainforests. But no comparable effort has gone into accounting for the vast farming sector.

Another obstacle to an agreement in the UN talks is the suspicion that rich countries will meet a large part of their emissions reductions by buying credits on the international carbon market rather than constraining their own industries.

Hill says he expected nothing more in the Copenhagen agreement than general statements that can be filled in later with details.

(Shanghai Daily June 8, 2009)