A growing number of papers co-authored by our colleagues Simon Lewis (Leeds/UCL) and Yadvinder Mahli (Oxford) are showing that tropical forests may be less vulnerable to climate change than previously thought. In the past, scientific models have predicted vast areas of rainforest die-back due to changes to temperature and rainfall. However, new evidence is suggesting the situation may not be so drastic.
In the first study reported this month, genetic analyses were used to estimate the ages of 12 widespread Amazonian tree species (Dick et al., 2013). They hypothesized that the older the species, the warmer the climate it has previously survived, with air temperatures during the Pliocene (2.6–5 Ma) and late-Miocene (8–10 Ma) across Amazonia being similar to 2100 temperature projections under low and high carbon emission scenarios, respectively. Their results showed that 9 of the 12 species were older than 2.6 million years, and therefore have experienced greater climatic warmth than the present time. They conclude that, in the absence of other major environmental changes, near-term high temperature-induced mass species extinction is unlikely.
In the second study, computer simulations with 22 climate models and the MOSES–TRIFFID land surface scheme were used to explore the response of tropical forests in the Americas, Africa and Asia to greenhouse gas-induced climate change (Huntingford et al., 2013). They found that only one of the simulations predicted biomass loss in tropical forests by the end of the twenty-first century—and then only for the Americas. The authors claim this study is the most comprehensive assessment yet of the risk of tropical forest dieback caused by climate change. The new projections are more refined, they say, because in part, they account for lower estimates of future warming and drying across Brazil than in older models, and they also account for the fact that tree growth is likely to be enhanced by higher carbon dioxide levels - a process known as carbon dioxide fertilisation. So, in the new models, losses in rainforests' ability to store carbon are largely balanced out by the positive effects of carbon dioxide fertilisation. However, caution is warned, as Simon Lewis points out; the past cannot be directly compared to the future. The Amazon forest is not only facing rapidly increasing air temperatures, but high atmospheric carbon dioxide concentrations, possible extreme droughts, and extensive human-induced fragmentation and deforestation. Lewis says: "resilience to climate change alone is not the same thing as resilience to climate change plus the other direct human impacts together."
Dick CW,
Lewis SL, Maslin M, Bermingham E (2013) Neogene origins and implied
warmth tolerance of Amazon tree species. Ecology and Evolution 3(1):
162-169.
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