The incredible shrinking Amazon rainforest; But is the rate of loss rising or declining?

• Author: Hirsch, Tim

The news coming out of the Amazon basin never seems to be good. Stories on rainforest losses generally use comparisons with U.S. states or countries of the world: since 1970, an area of rainforest the size of Texas has been lost; in the worst year of deforestation, 1995, an area equivalent to Belgium went under the chainsaw and the match.

Apart from emphasizing the sheer scale of the mightiest rainforest in the world--even the loss of a Texas-sized patch leaves more than 80 percent of it intact--these comparisons are not very useful for helping the concerned citizen judge what is really going on in the Amazon. What matters to most people is whether deforestation is coming under control, or whether this magnificent ecosystem is doomed to relentless decline, with all the implications for the millions of unique species it harbors, for the survival of precarious indigenous cultures, and for the global climate.

A better way of getting a handle on this question is to look at trends over time. And here the news of recent years has offered a glimmer of hope (see figure, right). Estimated annual deforestation figures for the Brazilian Amazon reveal a marked drop in the rate of forest loss over the past three years. After reaching a peak of more than 27,000 square kilometers in 2004, it fell to "only" 11,000 square kilometers lost between August 1,2006 and August 1,2007, the period used for these purposes in the release of satellite-derived data for year-to-year comparisons.

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That still means the annual loss of an area of forest larger than Lebanon (sorry to go back to those comparisons), but it represents a drop of nearly 60 percent in the deforestation rate. The figures for last year were the lowest since the early 1990s, so it is not surprising that the Brazilian government has been using them as evidence of success for the anti-deforestation measures introduced under the administration of President Luiz Inacio Lula da Silva.

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A downward trend in deforestation has taken on added importance since the Bali climate conference in December 2007. One of the key decisions there was to launch a process looking at financial incentives to reward developing countries that protect their forests, in recognition of the fact that something like one-fifth of all human-caused greenhouse gas emissions are accounted for by deforestation. The trajectory of rainforest loss, in other words, could have very significant implications for Brazil's income in the years ahead.

So any suggestion that the trend of Amazon destruction is starting to move upwards again is bound to be politically explosive. And it was precisely such a bombshell that the Brazilian National Space Research Agency (INPE) dropped in January this year.

Satellite States

To understand the significance of what the new data were showing, it is worth backing up a bit to describe how the Brazilian government goes about measuring and reporting the scale of deforestation in the Amazon.

Until 2005, the only method was the Amazon Deforestation Estimate Project (PRODES, the Portuguese acronym), an annual analysis of around 200 high-resolution images taken of the Amazon region by the NASA Landsat satellite, supplemented by other satellite data when there are problems of cloud cover. By comparing vegetation cover within each image with those of the previous year, it is possible to get a pretty accurate estimate of the deforestation that has taken place in those 12 months.

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The problem with this system is that by the time the complex analysis of each year's deforestation is complete, the damage has long since been done. It serves only as a historical record and is of little use in aiding the authorities to chase after illegal deforesters. So in 2005 a new system was...