Could it be? Things are changing so quickly in the Amazon that it’s hard to come up with a satisfactory explanation of anything, but the latest deforestation statistics certainly make you wonder.

Here’s the gist: Brazil’s National Institute for Space Research issued preliminary satellite data last week indicating that the rate of deforestation dropped by 47.5 percent, from 4,375 to 2,296 square kilometres, in 2010. (Beware: the English version contains an error with these specific numbers) This is low-resolution satellite data, so the official number (which no one really disputes) will be substantially higher when it comes out in December. But it is an apples-to-apples comparison.

The final tally for 2009 was 7,464 square kilometres, and the 2010 total is expected to register below 4,000 square kilometres. That would represent an 85 percent drop compared to the recent peak year of 2004, when 27,772 square kilometres were chopped down. It would also mean that Brazil has met its commitment to reduce deforestation by 80 percent by 2020 a decade early, says Doug Boucher, who heads the tropical forest programme for UCS. “That’s a remarkable achievement."

Boucher translates an 80-percent reduction from the long-term baseline (roughly 19,500 square kilometres between 1996 and 2005) into an annual reduction of about 1 gigatonne of carbon dioxide emissions. That is equivalent to roughly 17 percent of the United States’ annual greenhouse gas emissions, which is about what the United States is promising to do by 2020. And the US commitment is roughly equivalent to what the European Union has committed to doing unilaterally between now and 2020.

In other words, if Brazil can prevent a major backslide, it will have accomplished as much in the past few years as the United States and Europe are committing to do over the next decade. And then there’s the added benefit to biodiversity.

Now, there are reasons to be wary.

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Brazil will of course claim that this is the result of tougher enforcement, and clearly that’s part of it. In addition to cracking down on those who blatantly break the law, serious efforts to clear up land ownership are under way. There is also domestic and international pressure on Brazilian ranchers and farmers, and the latter comes along with funding (see earlier coverage here and here)

But we are in the midst of a serious economic crisis, which dampens demand for nearly everything and could take some pressure off the forest. Then again, food prices shot up a couple of short years ago and remain well above earlier levels for things like soy. Moreover, Brazil’s economy is still booming.

Who knows what will happen next year (ominously, fire activity apparently increased in August). Nobody thinks the trend is on a direct line to zero, which is to say that the rate is likely to start bouncing around at some point. But the graph above, showing the evolution of the size of forest clearings in hectares, helps put things into perspective. In 2002, 75 percent of the deforestation took place on patches larger than 100 hectares. Last year, that same category of large clearings made up just 15 percent of the total.

In other words, what is disappearing is the massive clear-cutting that can only be conducted by wealthy landowners and businesses that flout government rules with impunity. That’s a place where enforcement can have an effect, and from this perspective, a key question is what will happen in Brazil’s elections this fall.