After a hollow Copenhagen accord, Secretary Clinton signed a bilateral agreement with Brazil this week to combat deforestation, a major cause of greenhouse gas emissions. "The United States and Brazil signed a memorandum of understanding to work together to slash greenhouse gas emissions from tropical deforestation, one of the main drivers of global climate change. The deal, signed by Secretary of State Hillary Rodham Clinton in Brasilia on Wednesday, marks the first time the two countries have formally agreed to work together on deforestation. In the past, Brazilian leaders have been wary of foreign interference in the Amazon, Earth's largest tropical forest. But climate scientists are raising loud alarms that the slashing and burning of forests, which cause about 15% of the emissions that are trapping heat in the atmosphere, threatens to dangerously disrupt the world's climate. Indonesia and Brazil are, respectively, the globe's third and fourth biggest emitters of carbon dioxide, after the U.S. and China, mainly because of how rapidly they are destroying their forests. In Copenhagen in December, a group of nations made progress in negotiating rules for quantifying the carbon saved by avoiding deforestation, so that credits could be used to offset industrial emissions, a program known as "Reducing Emissions from Deforestation and Degradation" -- or REDD."