Amazon forest faces climate catastrophe

Posted: 26 November 2002

The Amazon basin - which contains 60 per cent of the world's rainforest - is threatened on two fronts: 'business as usual' emissions of greenhouse gases and accelerating deforestation for commercial development. The result, says a new authoritative report, could be devastating - not only for South America but for the global climate.

The report, Climate and the Amazon: Consequences for our Planet, warns that once a critical threshold of deforestation is passed, the self-sustaining water cycle - unique to the Amazon - will break down irrevocably, leading to a general drying out of the forest. This would not only cause a dramatic and sudden collapse of the entire of the entire ecosystem, but impact on the climate of developing and developed countries alike - including the United States.

Amazon rainforestA Bartschi/Still PicturesThese conclusions are based largely on the work of Dr Peter Cox and Dr Richard Betts from the UK Meteorological Office at the Hadley Centre and Professor Roni Avissar from Duke University in the United States. They reported their findings to a conference on 'World Climate in Danger: the Amazon Connection' held in London in October, 2002.

Drying forest

The pioneering models from the Hadley Centre indicate that the increase in surface temperatures as a result of global warming will give rise within the next few decades to abrupt changes in rainfall over the Amazon Basin, leading to a drying out of the already fragmented forest and to more forest fires. This in turn will release vast quantities of greenhouse gases and accentuate the surface temperature rise and the El Niño conditions.

Professor Avissar has complemented this work by showing how convection processes over the Amazon give rise to giant thunderclouds, which can transfer large amounts of energy to higher latitudes. One important result is the direct interaction between rainfall in the Amazon and in the corn-belt region of the United States. Heavier winter rainfall over the Amazon, for example, is reflected in increased rainfall several months later over parts of the United States, during the critical period for crop growth.

Reporting on these findings, Peter Bunyard, Science Editor of The Ecologist magazine, says, "We are in immediate danger of radically transforming the climate of South America. Furthermore, it becomes crystal clear that the current wisdom of conserving a large proportion of biodiversity in the Amazon Basin by putting in place a patchwork of protected areas of forest and connecting corridors will fail catastrophically unless significant areas of forest remain.

"It is therefore of the utmost urgency that banks, aid agencies, developers and indeed governments, know much more about the Amazon Basin as a vital component of global climate, before they embark on their grandiose plans for clearing large swathes of forest to further their own commercial interest."

Bunyard reports that by 1998, the Brazilian Amazon had lost some 549,000 square kilometres of forest cover - an area about the size of France out of a total area as large as Western Europe. In the past half century the population in the dry south has grown from 2 million to 20 million as poor peasants and agribusiness moved in. And with people have come fires that have destroyed vast areas of forest.

Development threat

Now, the national Avanca Brasil development plan anticipates an investment of more than $40 billion over the next five years to grow vast quantities of Soya, build roads and dams, extract timber, develop new mining projects and develop massive new agro-projects. Experts warn that over the next 15-20 years Avanca Brasil could accelerate the process of degradation so that more than 40 per cent of the forest will have vanished. And that left standing will be highly fragmented and vulnerable to further encroachment.

Meanwhile, the hope is that the G7 developed countries and the European Community will provide $340 millions to set up a pilot scheme to conserve the Brazilian rainforest. The aim would be to bring about effective land-use planning, establish ecological corridors to link remaining patches of bio diverse-rich forest, and protect indigenous areas and national parks.

However, scientific modelling and verification through observation shows that the idea of salvaging patches of diversity, and leaving as little as 10 per cent of the forest intact, is pointless "unless conservationists take as their starting point the need to protect climatic processes that are dynamically connected to the forest on the ground", says Bunyard.

Domino effect

Using an elaborate climate-vegetation model, climatologists from the Hadley Centre and Reading University found that on present trends, the global climate would become more like that of an El Niño year and precipitation would fall by 2 or millimetres per day on average over Amazonia.

This would produce a devastating knock-on effect for the region: "the trees would transpire less and so put less water back into the atmosphere. The net consequence is that the forest begins to dieback, not only fuelling the atmosphere with more greenhouse gases, but also further diminishing evapotranspiration. That 'positive' feedback leads to further die-back and ultimately the loss of much of the natural forest of Amazonia."

In turn, the result would be catastrophic for the global climate and the environment at large. The loss of carbon from vegetation and the soil in Amazonia would increase the current level of carbon dioxide in the atmosphere by one-fifth, which would result in an increase in global temperature by 8 degrees centigrade - more than 50 per cent higher than figure reported by the International Panel on Climate Change in its 2000 report on global warming. This would take global temperatures levels not seen on earth for more than 40 million years when the earth had no permanent ice sheets.

The report offers a stark warning on the effects of deforestation on climate. "In essence, the climate perturbation you would expect by only considering carbon emissions could be smaller than that which you would expect if you considered both carbon emissions and reduced evapotranspiration. You might therefore take the view that a tonne of carbon emitted by Amazon deforestation is even worse than a tonne of carbon emitted from fossil fuel burning, because of the extra climatic effects of evapotransporation. Unfortunately, the protocol drawn up in Kyoto does not consider this point, Bunyard concludes.

For a copy of the report, Climate and the Amazon: Consequences for our Planet, please contact Peter Bunyard.