Tailandia, Brazil ? For more than a decade, Vigilio de Souza Pereira has carved his living out of the thick Amazon rain forest around his ranch in northern Brazil.

When Pereira needs more land for his crops and cattle, he cuts more virgin jungle and sets the vegetation ablaze. When the nutrient-poor soil has been depleted, he moves on and cuts down more jungle.

Such slash-and-burn agriculture has helped the 51-year-old Pereira and millions of other farmers and ranchers scratch out a living from the forest, but it’s put Brazil at the heart of the environmental challenge of the century.

As vast tracts of rain forest are cleared, Brazil has become the world’s fourth-largest producer of the greenhouse gases that cause global warming, after the United States, China and Indonesia, according to the most recent data from the U.S.-based World Resources Institute.

And while about three-quarters of the greenhouse gases emitted around the world come from power plants, transportation and industrial activity, more than 70 percent of Brazil’s emissions comes from deforestation.

Making a case

Burning and cutting the forest releases hundreds of millions of tons of carbon dioxide, methane and other gases that the vegetation had trapped. Those gases collect in the atmosphere, prevent heat from escaping and help raise the Earth’s temperature.

Keeping greenhouse gases out of the atmosphere has become crucial to saving the planet from catastrophic climate change, scientists say. However, stopping the destruction of the vast Amazon rain forest means confronting the region’s lawlessness and persuading Brazilians such as Pereira to leave the forest alone.

“Brazil has a huge amount of forest that’s still there, and that means Brazil has a much greater role in terms of future deforestation,” said Philip Fearnside, a research professor at Brazil’s National Institute for Amazon Research. “Any changes that happen here have great influence on whether the Earth gets warmer.”

A Connecticut-sized chunk

The 1.5-million-square-mile Brazilian Amazon, larger than the entire nation of India, contains more than 40 percent of the world’s rain forests, and about a fifth of it already has disappeared, mostly in an “arc of deforestation” along the forest’s southern and eastern edges.

Every year, another chunk of forest the size of Connecticut or larger disappears as farmers, illegal loggers and others clear jungle, mostly without government approval. Violent clashes over land are common, as are murders of environmentalists.

The effects of the Amazon’s continued destruction could be especially severe in southern Brazil, where much of the country’s agriculture, industry and population is based. About 40 percent of the precipitation there comes from moisture evaporated off the rain forest’s thick tree cover. Cutting back more of the Amazon could mean starving the area of water.

Veteran diplomat Sergio Serra, who in April was named Brazil’s first ambassador in charge of global warming issues, said his country is doing its part by, among other things, strengthening enforcement of environmental laws and creating vast forest reserves.

As a result, he said, the rate of deforestation in the Amazon dropped by about 50 percent from August 2004 to July 2006. Environmentalists said lower global prices for soybeans grown in the Amazon, as well as tougher enforcement, help explain the drop.

“Brazil is conscious of its responsibilities,” Serra said. “We are already combating the problem with more vigor, and that led to this significant decline.”

Persuading agribusiness

Convincing millions of people that they can make more money by leaving the trees alone than by cutting them down is key to saving more of the forest. Already, some farmers are cutting trees selectively and selling the wood as “green” lumber for multiples of the price they’d get for illegal wood.

Environmentalists say Brazil also could take part in an international market of carbon credits that would pay people not to cut down forest. Brazil’s government opposes such a carbon market because it wouldn’t reduce greenhouse gas emissions, Serra said.

Persuading agribusiness giants to stop buying soybeans and other crops grown on deforested land is also crucial, many said.

“The important thing that we want to show is that if you don’t create economic stimulus for protection, it’ll be very difficult to have any quick action,” said Jose Heder Benatti, the president of a land management agency in the state of Para. “Because we live in a capitalist country, the market is a strong force for action.”

Pereira, the farmer, said he was open to such ideas, although he hadn’t yet seen how he could make as much money conserving his land as he does clearing it for cattle, soybeans and other crops.

Sticking to the status quo, however, isn’t a solution, he said.

“If the forest doesn’t exist anymore, our colony will end,” he said. “Without the forest, there won’t be any rain or any crops.”