40 per cent of Amazon rainforest at 'tipping point' of becoming savannah
Forty per cent of the Amazon rainforest is at risk of becoming grassy savannah if climate change rates continue, scientists have found.
This is far more than previously thought, according to a study using computer models and data analysis, published today in the journal Nature Communications.
Scientists at Utrecht University found that rainfall in 40 per cent of the Amazon is at a 'tipping point', where it could exist in either state, as rainforest or savannah.
Rainforests, with their dense trees, create their own rainfall as leaves give off water vapour, which then falls down as rain. Fire and prolonged droughts caused by climate change cause trees to die off. The more trees are removed, the less rain falls, and so the ecosystem changes.
Tropical rainforests need at least 100 inches of rainfall per year, and support the greatest number of species of any other type of biome on the planet. Savannah is grassland interspersed with trees, which is far less biodiverse.
Lead author Dr Arie Staal said: "In around 40 percent of the Amazon, the rainfall is now at a level where the forest could exist in either state - rainforest or savannah, according to our findings."
She warned this trend is expected to worsen as the region warms due to rising greenhouse gas emissions.
The rising deforestation in the Amazon, coupled with the fires burning now, are also putting more of it under threat of joining the "tipping point".
Dr Stall explained: "The dynamics of tropical forests is interesting. As forests grow and spread across a region this affects rainfall - forests create their own rain because leaves give off water vapour and this falls as rain further downwind. Rainfall means fewer fires leading to even more forests."
Once changed to savannah, it would take decades for the forest to return to its natural state, if it ever did at all.
Researchers also modeled what would happen to the amazon under the very high-emissions scenario used by the Intergovernmental Panel on Climate Change (IPCC).
Overall, the researchers found that as emissions grow, more parts of the Amazon lose their natural resilience, become unstable and more likely to dry out and switch to become a savannah-type ecosystem. They note that even the most resilient part of the rainforest shrinks in area. In other words, more of the rainforest is prone to crossing a tipping point as emissions of greenhouse gases reach very high levels.
The Amazon is one of the global rainforests at highest risk of disappearing as a result of deforestation because its rainfall depends on tree cover.
The academics found that the minimal and maximal extents of the rainforests of Indonesia and Malaysia are relatively stable because their rainfall is more dependent on the ocean around them than on rainfall generated as a result of forest cover.
Ingo Fetzer of the Stockholm Resilience Centre, co-author of the paper, said: “We understand now that rainforests on all continents are very sensitive to global change and can rapidly lose their ability to adapt. Once gone, their recovery will take many decades to return to their original state. And given that rainforests host the majority of all global species, all this will be forever lost.”
