The 2,700 pigs on the farm 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 UN scientists says 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 in December on ways to reduce emissions and help countries adapt to changes in climate. They will reconvene June 1 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 the global population increases and living standards rise in developing countries where more people are eating meat.

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.

When the FAO report came out in 2006, "people in the livestock sector were shocked because they thought they did a good job," says Akke van der Zijpp, a professor of animal husbandry at Wageningen University, a premier Dutch technical facility. Now they "are becoming slowly aware that this problem has to be solved."

One way to deal with it is to reduce the methane animals produce by changing their diet or through 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 euro177 ($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 (141,250 cubic feet) 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 nonprofit 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.

Last year, Horrevorts said, a British offset provider paid euro5 ($6.70) per ton for people wanting to neutralize plane travel or rock concert tickets. This year, the farm was negotiating with a Dutch company seeking to become carbon neutral to promote a green image.

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

Horrevorts, who is a biological researcher rather than a professional farmer, says that with financial incentives through electricity subsidies, it could become standard practice for ordinary farmers. About 50 commercial biogas plants operate on farms in the Netherlands, and the practice is spreading across industrial livestock farms around the world.

"I think in the future every pig farm will have a biogas plant," he says.

But at euro1 million (US$1.3 million) for a big plant like Sterksel's, it's a rich man's 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.

"It sounds like a big pot," Hill said, but dealing with farming is tougher than with industries. "You're talking about tens of thousands of sources of industrial emissions in rich countries. That's a lot more manageable than hundreds of millions of agricultural operations."

Measuring and verifying carbon reductions from soil conservation, grassland management and livestock is complicated, and those reductions may not be permanent. Trees planted to soak up carbon from the air, for example, can always be cut down and burned.

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. In other words, they would buy credits from farmers to reduce their carbon footprint, in the same way the offset company bought credits from the Sterksel pig farm.

"If the idea is that rich countries will do most of their reductions through offsets, a lot of developing countries have a big problem with that," says Hill, speaking from his home base in Bolivia.

Hill says he expected nothing more in the Copenhagen agreement than "place holders," or general statements that can be filled in later with details. But Smith, the scientist from Aberdeen who co-wrote the agriculture section in the 2007 report by the UN's Intergovernmental Panel on Climate Change, says including agriculture in the Copenhagen agreement would provide a source of capital from rich countries to poor ones.

"It would be a desperate shame if it were blocked for political reasons," he says.

(China Daily June 1, 2009)