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Limiting global warming to 2 °C is unlikely to save most coral reefs


Mass coral bleaching events have become a widespread phenomenon causing serious concerns with regard to the survival of corals. Triggered by high ocean temperatures, bleaching events are projected to increase in frequency and intensity. Here, we provide a comprehensive global study of coral bleaching in terms of global mean temperature change, based on an extended set of emissions scenarios and models. We show that preserving >10% of coral reefs worldwide would require limiting warming to below 1.5 °C (atmosphere–ocean general circulation models (AOGCMs) range: 1.3–1.8 °C) relative to pre-industrial levels. Even under optimistic assumptions regarding corals’ thermal adaptation, one-third (9–60%, 68% uncertainty range) of the world’s coral reefs are projected to be subject to long-term degradation under the most optimistic new IPCC emissions scenario, RCP3-PD. Under RCP4.5 this fraction increases to two-thirds (30–88%, 68% uncertainty range). Possible effects of ocean acidification reducing thermal tolerance are assessed within a sensitivity experiment.

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Figure 1: Heat stress projections at the example location of Tuvalu (10.75° S, 180°).
Figure 2: Thermal stress at different levels of global warming.
Figure 3: Projected probabilistic fraction of the world’s coral reefs subject to long-term degradation under the RCPs.


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The work on this analysis was supported by the UFOPLAN project FKZ 370841103 through the German Federal Environment Agency and by the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (11_II_093_Global_A_SIDS and LDCs). We thank J. Rogelj for his very helpful comments on the manuscript. O.H-G. would like to recognize support from the Australian Research Council Centre of Excellence in Reef Studies and the Global Change Institute. We acknowledge the modelling groups, the Program for Climate Model Diagnosis and Intercomparison and the WCRP1’s Working Group on Coupled Modelling for making available the WCRP CMIP3 multi-model data set.

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A.G., K.F. and M. Meinshausen contributed equally to this paper. K.F. and M. Meinshausen designed the study. A.G., K.L. and M. Mengel analysed data with contributions by K.F. and M. Meinshausen. M. Meinshausen, K.F., S.D. and O.H-G. wrote the paper.

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Correspondence to K. Frieler.

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Frieler, K., Meinshausen, M., Golly, A. et al. Limiting global warming to 2 °C is unlikely to save most coral reefs. Nature Clim Change 3, 165–170 (2013).

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