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Predictions for the forest

Models show that part of the Amazon is going to turn into savannah and suggest that the effects of global warming may be reduced if the clearance of vegetation is avoided

PAULO ARTAXOBurning vegetation in the Amazon: the challenge is to reduce vegetation clearance by 50% and stay at this level until the end of the centuryPAULO ARTAXO

Two scientific articles published last month have made predictions for the future of tropical forests based on computer calculations and models. For example, they point to the strong probability of global warming converting part of Brazil’s Amazon area into savannah land as a result of the reduction in the amount of water in the soil. But on the other hand, both the global changes and their effects on the vegetation cover may be lessened if mankind reduces the clearance of vegetation.  The articles were written by several scientists and all are also signed by a Brazilian, Carlos Nobre, a researcher from the Weather Forecast and Climate Studies Center (CPTEC) at the National Space Research Institute (Inpe) and a member of the Inter-governmental Panel on Climate Change (IPCC), a United Nations forum.

The study “Tropical forests, climate change and climate policy” was published on the Science journal website and shows that if vegetation clearance continues at the same pace as over the last few years the destruction of tropical forests will launch an additional 87-130 billion tons of carbon into the atmosphere by 2100, the equivalent of more than a decade of emissions caused by fossil fuels. But if countries succeed in reducing the rates of vegetation clearance by 50% by 2050 and maintain the same pace until 2100 it will be possible to eliminate 50 billion tons of carbon. This is equal to more than 10% of the cuts needed to keep atmospheric concentrations of carbon dioxide at 450 parts per million, the level above which, according to the IPCC, global warming will exceed 2º C and produce problems on a global scale. The text is also signed by scientists from Australia, Canada, the United States, France and the United Kingdom and is featured in the Policy Forum section, in which Science recommends studies that are applicable to public policies.

For a very long time now developed countries have been accused of being responsible for most of the emission of greenhouse gases and this has led scientists to put developing nations’ potential for emission reduction on the backburner. These nations were not included in the first phase of the Kyoto Protocol pledges, but all this is changing. According to data from the IPCC, in the 1990s the clearance of tropical forests released into the atmosphere nearly 1.5 billion tons of carbon a year, or 20% of the greenhouse gas emissions caused by man. Recently, under the aegis of the UN Convention on Climate Change, an initiative arose that was aimed at identifying those policies capable of reducing emissions due to vegetation clearance in developing countries. It was this initiative that provided the data used in the study published on the Science website.

Declining Numbers
In addition to the importance of controlling the devastation, the article suggests that this type of initiative is one of the cheapest options for containing vegetation clearance. Researchers point out, however, that developing countries need financial support to reduce the devastation. “There has to be a global effort and part of the reduction needs to be financed by rich nations”, says Carlos Nobre.

The good news is that Brazil, in Nobre’s opinion, has ample opportunity to reach this 50% reduction target long before 2050. “The pace of clearance in Brazil is slowing and I’m optimistic about our capacity to keep it under control in the future”, he states. “For the first time public authorities have taken effective actions to curb the organized crime that cuts down the forest and we’re already seeing the impact of this. On the other hand, the Brazilian population will tend to stabilize over the next few decades and the enormous areas that have already been cleared are more than enough to accommodate the economic activities of the current rural population and those resulting from the projected increase in this population. Brazil needs to commit to this but the outlook is favorable”, he declares. The case of the tropical forests in Indonesia, on the other hand, is more complex, according to the researcher. “Institutional control there is more complicated and as a lot has already been cleared; what is left is particularly vulnerable.”

The second study, published in the magazine Geophysical Research Letters, in partnership with researchers Luis Salazar, from Inpe, and Marcos Oyama, from the Aerospace Technical Center, used 15 available computer-based climate models to estimate the impact of global warming on South American biomes. These models still have major  differences, as in the case of rainfall, for example. “There is controversy about the role of clouds, for example, which are difficult to represent in the models”, says Nobre. An increase in evaporation should encourage cloud formation, which by reflecting solar radiation, may serve to counteract warming and counterbalance the effects of global changes. This type of uncertainty also makes it unfeasible, for example, to foresee what will to happen to the Brazilian caatinga [scrubland vegetation, unique to Northern Brazil]. But, there is one important thing that all agree on. More than 75% of the models converge and indicate the probability of the southeastern Amazon region, mainly the forests of Para State, becoming a savannah.

“This region already has a longer dry season than other areas of the forest. The models indicate that with greater evaporation and the consequent reduction in the amount of water in the soil, it may become similar to parts of Goiás and Tocantins”, says Carlos Nobre. The researcher, however, avoids comparing the biodiversity that will remain within the cerrado [open pasture-land with some stunted tree vegetation]. “It’s going to be a savannah that’s a lot poorer”, he says. The estimates indicate an 18% reduction in the areas covered by tropical forests by the end of this century, with a 30.4% increase in savannah covered areas.

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