Amazon rainforest

19/07/2010

Predictions Revisited and Climate Change: News and Comments

Will the Amazon rainforest survive?

A flurry of stories about the rainforests confirms that the proper concern about tropical deforestation has been thoroughly confused by improper attempts to invoke man-made global warming. Before turning to thunderstorms felling trees,  let’s start with the big picture of expectations, past and present, for the Amazon rainforest. For more than 30 years, large-scale assessments have been based on satellite imagery, despite the problem that much of the forest is covered with clouds at any one time. Brazil’s own Instituto Nacional de Pesquisas Espaciais, INPE, has played a leading part.

In a forecast that proved wrong even more rapidly than The Population Bomb (see the previous post) an ecologist Philip Fearnside declared in 1982 that the Amazon forest was vanishing at an accelerating rate, with more than 40% to be gone by 1988. I told the tale in my 1991 book about remote sensing, Spaceship Earth, after visiting INPE in São Paulo.

During the 1980s Brazil found itself at war on two fronts. At home, the government tried to moderate the rate of clearances in the Amazonian forest, and police a frontier region as gun-happy as the old Wild West of the USA. Internationally, they had to deal with a rising chorus of criticism about the rate at which the forest was disappearing. In 1982, on the basis of INPE’s figures, predictions by an American scientist P.M. Fearnside amounted to a forecast that 44 per cent of the Amazonian forest would be lost by 1988.

The Brazilians greeted such estimates with frank disbelief. There then followed a contest between calculation and remote sensing to try to establish the true facts. …

In 1989, the World Bank published estimates indicating that 12 per cent of Legal Amazonia was already deforested by 1988. This was based on calculations from the state of affairs in 1980. By this time the Brazilians were growing very angry. Although the figure was far less than the Fearnside estimate, the fact that it came from the World Bank secured it a place in international environmental folklore. The Brazilians appealed again to the umpires in space: the unblinking instruments of the remote-sensing satellites.

At INPE, Roberto Pereira da Cunha decided to make a ‘wall-to-wall’ assessrnent of the deforestation in Legal Amazonia. As he remarked, ‘No one wants to do the dirty work of gathering the data. It is a very trivial task for scientists.’ Trivial, but not unlaborious. Pereira’s team assembled 234 Landsat scenes and selected for close interpretation 101 images that showed evidence of deforestation. From colour composites of three wavelength bands the scientists outlined the deforested patches, and used a grid to measure their areas. Images for different years established rates of deforestation.

The most important conclusion was that there was no acceleration: deforestation was proceeding at a more or less steady rate. As for the total recent deforestation up till the end of 1988, INPE’S answer was 5 per cent of the area of Legal Amazonia. Meanwhile, Fearnside had changed his forecast. His new figures indicated 7 per cent deforestation of Legal Amazonia by 1989 – a far cry from his 44 per cent figure of just 7 years earlier, and almost in line with INPE’s figure. In 1990 Jim Tucker and Chris Justice of NASA broadly confirmed the Brazilian result by a similar large-scale use of Landsat imagery, but with a different technique, using only a single infra-red channel.

So what do the umpires in space say now, two decades later?

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