Abstract ID: 63

A tipping point in the Amazon? Exploring the likelihood and mechanism of a climate-change induced dieback of the Amazon rainforest

We examine the evidence for the suggestion that 21st century atmospheric change may cause a climate-driven dieback of Amazonian forest. We utilise remotely sensed land cover and precipitation data to examine the climatic limits of Amazonian forests. We then evaluate 19 Global Climate Models (GCMs) against modern observed climatology and climate thresholds for rainforest, and discount those GCMs that are unable to predict the presence of extensive rainforest in Amazonia in the 21st century. When we consider the selected GCMs alone under the A2 emissions scenario, all indicate a tendency to enhanced dry season water stress over the 21st century, with 50% of models suggesting that this drying may be sufficiently severe to tip the rainforest zones into a climate more suitable for savanna. However, once the fact that all GCMs substantially estimate wet season rainfall is taken into consideration, a transition to a more seasonal forest regime is more likely than &ldquosavannization&rdquo. These seasonal forests may be resilient to seasonal drought, but are likely to be vulnerable to seasonal fires, which are naturally rare in much of Amazonia. The spread of fire ignition points associated with advancing deforestation, logging and fragmentation may act as nucleation points that trigger the transition of these seasonal forests into fire-dominated, low biomass forests. With or without the spread of fire events, substantial alteration in species composition and decline in diversity are likely to accompany intensifying seasonality. If it occurs, the dieback of the eastern Amazonian forests is likely to be a result of the synergy between intensified seasonality and advancing deforestation and fire.

Session:  Fire - Fire, drought, and changes in vegetation structure and composition

Presentation Type:  Oral