Warming 'may harm rainforests less'

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The world’s rainforests may be able to weather the assaults of climate change more robustly than scientists had earlier thought, says a new study.

LONDON, 12 March – Scientists think they have found some good news for the Amazon and other tropical forests. They say they appear more able to withstand the effects of climate change than previous studies had suggested.

The research team, including climate scientists and tropical ecologists from the UK, USA, Australia and Brazil, concluded that the forests are less likely to lose biomass – plants and plant material – in response to greenhouse gas emissions over the rest of this century.

In what they say is the most comprehensive assessment yet of the risk of tropical forest dieback caused by climate change, the scientists say their results have important implications for the future evolution of rainforests, including the role they play in the global climate system and carbon cycle. The study is published online in Nature Geoscience.

To remain effective, programmes such as the United Nations’ Reducing Emissions from Deforestation and Degradation+ scheme (REDD+) require rainforest stability, in effect locking carbon within the trees.

The research team was led by Dr Chris Huntingford from the Centre for Ecology & Hydrology in the UK. He and his colleagues used computer simulations with 22 climate models to explore the response of tropical forests in the Americas, Africa and Asia to greenhouse gas-induced climate change.

They found loss of forest cover in only one model, and only in the Americas. The researchers found the largest source of uncertainty in the projections to be differences in how plant physiological processes are represented, rather than the choice of emission scenario and differences between various climate projections.

Although this work suggests that the risk of climate-induced damage to tropical forests will be relatively small, the team does list where the considerable uncertainties remain in defining how ecosystems respond to global warming.

Dr Huntingford said: “The big surprise in our analysis is that uncertainties in ecological models of the rainforest are significantly larger than uncertainties from differences in climate projections.

Other factors involved

“Despite this we conclude that, based on current knowledge of expected climate change and ecological response, there is evidence of forest resilience for the Americas (Amazonia and Central America), Africa and Asia.”

Co-author Dr David Galbraith, from the University of Leeds, UK, said: “This study highlights why we must improve our understanding of how tropical forests respond to increasing temperature and drought.

“Different vegetation models currently simulate remarkable variability in forest sensitivity to climate change. And while these new results suggest that tropical forests may be quite resilient to warming, it is important also to remember that other factors not included in this study, such as fire and deforestation, will also affect the carbon stored in tropical forests.

“Their impacts are also difficult to simulate. It is therefore critical that modelling studies are accompanied by further comprehensive forest observations.”

Co-author Dr Lina Mercado from the University of Exeter, UK, and the Centre for Ecology & Hydrology said one of the big remaining challenges was to include, in Earth system models, a full representation of how the rainforests respond and adapt to warming.

Debate over how resilient the rainforests may be is not new. A 2010 study, funded by Nasa, said the worst drought in the Amazon for more than a century had had little impact on the forest’s vegetation.

The Intergovernmental Panel on Climate Change (IPCC) has said that up to 40% of the Amazon forest could react drastically to even a small reduction in rainfall, and the result could be the replacement of the trees by tropical grassland.

One feature of this study is the confidence it has in climate projections and its acknowledgement that there is still much more to learn about plant physiology and ecosystem response.

Dr Huntingford told the Climate News Network the fertilisation effect of the large quantities of CO2 being absorbed by the forests was dominant, with the detrimental effects of climate change less important.

But the release of carbon dioxide into the atmosphere would overtake the process of photosynthesis. He said: “We do realise the story is changing as time passes, and all we can do is to try to present the facts as best we can and reflect the way the climate is changing, and the physical response to that now and in the future.” – Climate News Network