RIO DE JANEIRO  Environmental groups hailed a decision this week by four of the world’s largest meat producers to ban the purchase of cattle from newly deforested areas of Brazil’s Amazon rain forest.

At a conference on Monday in São Paulo organized by Greenpeace, the four cattle companies  Bertin, JBS-Friboi, Marfrig and Minerva  agreed to support Greenpeace’s call for an end to the deforestation.

Brazil has the world’s largest cattle herd and is the world’s largest beef exporter, but it is also the fourth largest producer of greenhouse gas emissions. Destruction of tropical forests around the world is estimated to be responsible for about 20 percent of global greenhouse gas emissions.

Greenpeace contends that the cattle industry in the Amazon is the biggest driver of global deforestation. But the Brazilian government, while pushing ambitious goals to slow deforestation in the Amazon, is also a major financer and shareholder in global beef and leather processors that profit from cattle raised in areas of the Amazon that have been destroyed, often illegally, according to Greenpeace.