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Saturday, February 14, 2009

Yadvinder Malhi et al., PNAS, Exploring the likelihood and mechanism of a climate-change-induced dieback of the Amazon rainforest

Proceedings of the National Academy of Sciences, February 13, 2009;

Exploring the likelihood and mechanism of a climate-change-induced dieback of the Amazon rainforest

  1. Yadvinder Malhia,1,
  2. Luiz E. O. C. Aragãoa,
  3. David Galbraithb,
  4. Chris Huntingfordc,
  5. Rosie Fisherd,
  6. Przemyslaw Zelazowskia,
  7. Stephen Sitche,
  8. Carol McSweeneya and
  9. Patrick Meirb
Edited by Hans Joachim Schellnhuber, Potsdam Institute for Climate Impact Research, Potsdam, Germany, and approved December 15, 2008 (received for review June 10, 2008)


We examine the evidence for the possibility that 21st-century climate change may cause a large-scale “dieback” or degradation of Amazonian rainforest. We employ a new framework for evaluating the rainfall regime of tropical forests and from this deduce precipitation-based boundaries for current forest viability. We then examine climate simulations by 19 global climate models (GCMs) in this context and find that most tend to underestimate current rainfall. GCMs also vary greatly in their projections of future climate change in Amazonia. We attempt to take into account the differences between GCM-simulated and observed rainfall regimes in the 20th century. Our analysis suggests that dry-season water stress is likely to increase in E. Amazonia over the 21st century, but the region tends toward a climate more appropriate to seasonal forest than to savanna. These seasonal forests may be resilient to seasonal drought but are likely to face intensified water stress caused by higher temperatures and to be vulnerable to fires, which are at present naturally rare in much of Amazonia. The spread of fire ignition 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. Conversely, deliberate limitation of deforestation and fire may be an effective intervention to maintain Amazonian forest resilience in the face of imposed 21st-century climate change. Such intervention may be enough to navigate E. Amazonia away from a possible “tipping point,” beyond which extensive rainforest would become unsustainable.

1To whom correspondence should be addressed. e-mail:
  • Author contributions: Y.M. designed research; Y.M., L.E.O.C.A., R.F., P.Z., and S.S. performed research; Y.M., L.E.O.C.A., D.G., R.F., P.Z., and C.M. analyzed data; and Y.M., C.H., S.S., and P.M. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission.

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