Climate-conscious groups warned that the U.S. decision Tuesday to end restrictions on Brazilian beef imports must not encourage greater deforestation in the Amazon if the world is to stop rising temperatures.

Scrapping the beef ban was a top priority for Brazil's agriculture sector, one of the few pistons firing in the country's stalled economy. For President Obama, getting Brazilian President Dilma Rousseff to agree to reforesting 12 million hectares by 2030 underscored the president's desire to lead at United Nations climate talks set to begin in late November in Paris.

"Since 2005, our two nations have reduced carbon emissions more than any other countries in the world. In Brazil, this includes very impressive efforts over the past decade to combat deforestation, including in the Amazon — what's sometimes called the 'lungs of the planet,'" Obama said at a joint press conference with Rousseff.

But for decades, cattle ranching was destroying those lungs.

Lax enforcement of Brazil's forest code, a 1960s law that requires landowners to leave 80 percent of land as forest, was a significant problem. Some are wary that high beef prices could encourage more to flout the law and were disappointed that the Obama administration didn't appear to put deforestation conditions on reopening the nation to Brazilian imports.

"The beef industry has been the largest cause of deforestation in the Amazon for at least a decade. Cattle ranchers pushing into virgin Amazon forest is the largest cause of greenhouse gas emissions in Brazil," Michael Wolosin, managing director of research and policy with Climate Advisers, told the Washington Examiner. "Increasing cattle production in Brazil could potentially exacerbate those problems."

Forests act as a carbon sink that swallow emissions emitted into the atmosphere. The World Wildlife Fund estimates that 15 percent of global emissions comes from deforestation. As such, reforestation is seen as one of the most significant ways Brazil could cut its global emissions. Rousseff previewed Brazil's post-2020 U.N. climate target to the Obama administration Tuesday, though she didn't publicly announce her government's goal, and both countries agreed to aim for getting one-fifth of their non-hydropower electricity from renewable sources by 2030.

"As countries that are as vast as continents, we have this very important greenhouse gas emissions target. We attach a great deal of importance to reduce not only deforestation, as we have done actually in Brazil, we have the commitment to come to a zero deforestation — or a zero illegal deforestation rate between now and 2030," Rousseff said Tuesday.

But since the U.S. established the ban two decades ago over concerns about foot-and-mouth disease from Brazilian beef, Brazil has significantly changed its cattle ranching practices, noted Doug Boucher, director of climate research and analysis with the Union of Concerned Scientists.

Pressure from environmental groups such as Greenpeace and Friends of the Earth compelled Brazilian food processors, supermarkets and slaughterhouses in 2009 to impose a moratorium on buying beef from deforested land. Ranchers changed their behavior to ensure their products could get to market, resulting in a drop in deforestation in the Brazilian state of Para, where the lower Amazon River flows into the sea, according to a May study led by Holly Gibbs, an assistant professor of geography and environmental studies at the University of Wisconsin-Madison. The study was published in Conservation Letters, a journal of the Society for Conservation Biology.

The beef policy, combined with a similar freeze on soybeans in 2006, helped curb deforestation three-quarters from 2005 through 2014 compared with the previous decade, Boucher said.

"Beef as a driver of deforestation has been controlled by a very substantial extent by the beef moratorium," Boucher said.

On top of that, Brazil has stepped up its enforcement of the forest code by cracking down on landowners using more than one-fifth of their land for agriculture. And Wolosin noted Brazil could improve its agriculture practices with some easy tweaks, as he said it has one of the lowest rates of cattle grazing per unit of land in the world.

But much of Brazilian cattle ranching occurs in lawless and hard-to-reach frontier areas, Wolosin said. Despite gains from the forest code, he said, "that law is broken quite frequently."

The victory on reforestation might also prove a mere accounting trick if it's not aggressive enough. Tuesday's announcement is sparse on specifics and Brazil had already planned a big reforestation push based on current laws. Steve Schwartzman, senior director of tropical forest policy at the Environmental Defense Fund, said the pledge failed to surpass those targets.

"It is, however, disappointing that President Rousseff's goal on deforestation ... goes no further than compliance with existing law," said Schwartzman, who said that at cutting deforestation 70 percent below historical averages since 2005 puts Brazil well on its way to meeting its goal of 80 percent by 2020.

Still, Boucher contended this was the first time the Rousseff regime has put a figure on the amount of forest it hopes to restore. Rousseff insisted Tuesday she was committed to reforestation — so if it's a question of from where is the beef, it won't be from illegally cleared land.

"We also wish to turn the page and engage in a clear-cut reforestation-oriented policy. That is an extremely important point for Brazil, and it also reflects the commitment we ourselves have undertaken as part of the forest code in effect in Brazil," she said.