Brazil's battle against deforestation was one of the big environmental success stories of the last decade. Between 2005 and 2012, the amount of Amazon rainforest cut down each year fell by 70 percent:

But the good news may not last. Deforestation in the Brazilian Amazon started rising slightly in 2013. And satellite data now suggests that the amount of forest being cleared away has been increasing sharply over the last half of 2014. (Credit to Richard Schiffman of New Scientist for pointing this out.)

The recent increase in deforestation was observed by Imazon, a Brazilian non-profit that uses satellite data to track forest loss. They've estimated that 1,660 square kilometers (640 square miles) of rainforest were cleared between August 2014 and January 2015. That's triple the amount cleared during the same period the previous year:

It remains to be seen if this is a lasting rebound or just noisy data — but a sustained increase would certainly be troubling.

Imazon's data shows a rise in deforestation all around the country. In the western states of Mato Grosso and Rondônia, forests are being burned and cleared away for cattle grazing and cropland. In the northern state of Para, illegal logging appears to be on the rise. Here's a map showing activity in January 2015. The red dots are deforestation:

Why does this matter? Because tree-clearing in the Amazon has been a major contributor to the rise of greenhouse-gases causing global warming — as those trees are burned, all the carbon they've stored goes up into the atmosphere.

Dwindling forest cover has also been a major reason for the decline of wildlife in the Amazon, one of the most species-rich places on Earth. "About two-thirds of all species on land are in tropical rainforests — and we're shrinking those rain forests," Stuart Pimm, a Duke University biologist, told me last year. "In the Americas, the greatest numbers of species on the brink of extinction are in the coastal forests of Brazil and the northern Andes and Ecuador."

Why deforestation in Brazil is rising again

So why is deforestation in Brazil starting to increase again after a decade of decline? It depends who you ask.

Some groups blame the government for weakening protections

Some environmentalists have blamed Brazilian President Dilma Rousseff for de-emphasizing rainforest protections since coming to office in 2011. Among other things, they argue that, back in 2012, Rousseff helped weaken the country's "Forest Code," which dictates the amount of forest that farmers and timber companies have to leave intact on their lands. The government also gave amnesty to people who cut down rainforest illegally before 2008 — possibly encouraging future illegal loggers to be more bold.

Rouseff's administration is also pushing a number of new dam projects that will degrade key forest areas. And she has been a proponent of major new highways, which, once built, often lead to further deforestation.

At the same time, the recent uptick is not entirely Roussef's fault. Experts had long warned that Brazil's decades-long success in curbing deforestation was never likely to last without major new policies. Deforestation in Brazil fell between 2005 and 2012 for a couple main reasons:

The government had pushed to protect more areas from logging and burning. The soybean and cattle industries came under heavy activist pressure to quit expanding through deforestation. So, in the last decade, farmers and ranchers had found ways to boost productivity on existing lands rather than clear forest for new space.

And it was always going to be tough for those trends to continue indefinitely. Brazil's government is now struggling to enforce further crackdowns on illegal logging, particularly as deforestation expands into remote parts of the jungle. Land speculators and arsonists are also learning to evade the environmental police.

Meanwhile, as the world economy keeps growing and demand for beef and soy keep rising, Brazil's industries are facing heavy pressure to find new land for these commodities. And there's only so much they can do to boost productivity on existing land. So, typically, that means clearing rainforest for new land.

Can Brazil pay farmers to stop cutting down rainforests?

Some experts now think it will be much more difficult for Brazil to stop deforestation than it has been in the past. It might also involve a lot more money.

One 2014 study in the Proceedings of the National Academies of Sciences argued that the Brazilian Amazon was at a "critical juncture." Current policies to stop deforestation have basically reached the limits of their effectiveness, the authors noted. The Brazilian government would have to resort to new tactics — that, unfortunately, would be much more difficult and expensive.

THE TACTICS THAT WORKED IN THE PAST WERE UNLIKELY TO WORK AS WELL IN THE FUTURE

Among other things, the study's authors found that deforestation in Brazil is largely shifting to remote areas — which are much harder for the government to protect. What's more, the authors noted that deforestation by smaller subsistence farmers is also rising sharply. Because these smaller farmers are often clearing forests for their livelihoods and subsistence, the government can't use the same crackdown techniques it used on larger corporations — to do so, the authors note, was likely to be "politically and socially problematic."

Instead, the authors noted that the government would likely need to turn to incentive-based programs that alleviate rural poverty or programs that essentially pay people not to cut down rainforests. But these programs are neither easy nor cheap. (Outside countries like Norway, Britain, and Germany have committed some $1 billion in financing through the REDD+ program to help Brazil reduce its greenhouse-gas emissions from forestry.)

"Further reductions in deforestation in the Amazon are challenging both because deforestation is happening in more, smaller, and remoter areas and is therefore harder to detect and more expensive to control," said lead author Javier Godar of the Stockhom Environment Institute, in a statement. "New approaches are needed, particularly to engage smallholders more."

Further reading

-- Here's our earlier story on how Brazil managed to reduce deforestation between 2005 and 2012

-- Note that deforestation is not a problem limited to Brazil. Forest clearances have increased dramatically in other Amazon countries like Peru and Bolivia. And Indonesia continues to see big losses. One recent study in Geophysical Research Letters found that tropical deforestation actually increased 62 percent between the 1990s and the 2000s — contrary to what the UN had earlier reported.

-- Over at Vice, Julie Ruvolo wrote a great piece about the many difficulties the Brazilian government has in curtailing illegal deforestation. One big problem? Regulators often don't know who owns what land — and hence who's allowed to clear forests legally.

-- NASA shows how dust from the Sahara Desert fertilizes the Amazon rainforest