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

Journal name:
Nature Climate Change
Year published:
Published online


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.

At a glance


  1. Heat stress projections at the example location of Tuvalu (10.75[deg][thinsp]S, 180[deg]).
    Figure 1: Heat stress projections at the example location of Tuvalu (10.75°S, 180°).

    Data from the mpi_echam5 model are shown in red whereas other AOGCM data are plotted in grey. a, Downscaled monthly SSTs of 19 AOGCMs (grey lines) anormalized relative to their maximum monthly mean (here, MMMmax) level over the 1980–1999 period, shown for scenario SRES A1B. b, Derived degree heating months for the same location. c, The recurrence frequency of exceeding DHM≥2°C×months in Tuvalu relative to the global mean temperature levels. Diagnostics for 19 individually analysed AOGCMs and the ex-post AOGCM average (thick grey line) are shown; the dashed red line corresponds to recurrence 1 in 5 years.

  2. Thermal stress at different levels of global warming.
    Figure 2: Thermal stress at different levels of global warming.

    ac, Frequency of DHM>2°C×month events with 1.0°C (a), 1.5°C (b) and 2.0°C (c) of global mean warming. Colour scale indicates the average of the 19 AOGCM-specific frequencies calculated at each coral reef grid point. Green points represent frequencies below 0.2yr−1 and yellow to red points represent frequencies above that critical limit for long-term degradation. d, Corals at risk of long-term degradation for constant thermal threshold DHM=2°C×month and individual AOGCMs. The average across 19 AOGCMs (thin blue lines) is shown as a thick grey line. e, Fraction of the world’s coral reef cells (coloured areas) at risk of long-term damage due to frequent (>1 in 5 years) coral bleaching events, depending on global mean temperature (xaxis) and assumed thermal threshold (y axis). A constant DHM=2°C×month thermal threshold is indicated by the horizontal dashed line. Two hundred random ensemble members for the 2050 climate state conditions under RCP3-PD with constant thermal threshold (white diamonds, black circled 1), thermal adaptation (white plus symbols, black circled 2), and aragonite-dependent thresholds (white circles, black circled 3) are shown.

  3. Projected probabilistic fraction of the world/'s coral reefs subject to long-term degradation under the RCPs.
    Figure 3: Projected probabilistic fraction of the world’s coral reefs subject to long-term degradation under the RCPs.

    a, Default projection, assuming a constant thermal threshold DHM=2°C×months and a five-year return period as leading to the demise of coral reefs. The colour steps mark the percentiles that are indicated at the colour bar in b. b, Under the scenario RCP3-PD, thermal adaptation (lower grey shaded areas), and aragonite-dependency (upper saturated blue shaded areas), decreases and increases the projected fraction of coral reef subject to long-term damage when compared with the default constant thermal threshold, respectively (see Table 1). See expanded Supplementary Fig. S5.


  1. Wilkinson, C. Status of Coral Reefs of The World: 2004 (Global Coral Reef Monitoring Network, 2004).
  2. Hoegh-Guldberg, O. et al. Coral reefs under rapid climate change and ocean acidification. Science 318, 17371742 (2007).
  3. Shamberger, K. E. F. et al. Calcification and organic production on a Hawaiian coral reef. Mar. Chem. 127, 6475 (2011).
  4. Bruno, J. F. & Selig, E. R. Regional decline of coral cover in the Indo-Pacific: Timing, extent, and subregional comparisons. PLoS ONE 2, e711 (2007).
  5. Hoegh-Guldberg, O. & Smith, G. J. The effect of sudden changes in temperature, light and salinity on the population–density and export of zooxanthellae from the reef corals Stylophora pistillata Esper and Seriatopora hystrix Dana. J. Exp. Mar. Biol. Ecol. 129, 279303 (1989).
  6. Eakin, C. M. et al. Caribbean corals in crisis: Record thermal stress, bleaching, and mortality in 2005. PLoS ONE 5, e13969 (2010).
  7. Baker, A., Glynn, P. W. & Riegl, B. Climate change and coral reef bleaching: An ecological assessment of long-term impacts, recovery trends and future outlook. Estuar. Coast. Shelf Sci. 80, 435471 (2008).
  8. Liu, G., Skirving, W. J. & Strong, A. E. Remote sensing of sea surface temperatures during 2002 barrier reef coral bleaching. Eos Trans. 84, 137144 (2003).
  9. Liu, G., Strong, A. E., Skirving, W. J. & Arzayus, L. F. 10th Int. Coral Reef Symp.17831793 (International Coral Reef Symposium (ICRS) Proceedings, 2004).
  10. Donner, S. D. Coping with commitment: Projected thermal stress on coral reefs under different future scenarios. Plos ONE 4, e5712 (2009).
  11. Donner, S. D., Skirving, W. J., Little, C. M., Oppenheimer, M. & Hoegh-Guldberg, O. Global assessment of coral bleaching and required rates of adaptation under climate change. Glob. Change Biol. 11, 22512265 (2005).
  12. Mitchell, J., Johns, T., Eagles, M., Ingram, W. & Davis, R. Towards the construction of climate change scenarios. Climatic Change 41, 547581 (1999).
  13. Simpson, M. C. et al. An Overview of Modelling Climate Change Impacts in the Caribbean Region with Contribution from the Pacific Islands (United Nations Development Programme, 2009).
  14. Hoeke, R. K., Jokiel, P. L., Buddemeier, R. W. & Brainard, R. E. Projected changes to growth and mortality of Hawaiian corals over the next 100 years. PLoS ONE 6, e18038 (2011).
  15. Donner, S. D, Knutson, T. R. & Oppenheimer, M. Model-based assessment of the role of human-induced climate change in the 2005 Caribbean coral bleaching event. Proc. Natl Acad. Sci. USA 104, 5483 (2007).
  16. Barshis, D. J. et al. Protein expression and genetic structure of the coral Porites lobata in an environmentally extreme Samoan back reef: Does host genotype limit phenotypic plasticity? Mol. Ecol. 19, 17051720 (2010).
  17. McClanahan, T. R. et al. in Ecological Studies Vol. 205 (ed. Caldwell, M. M.) 121138 (Springer, 2009).
  18. Yee, S. H., Santavy, D. L. & Barron, M. G. Comparing environmental influences on coral bleaching across and within species using clustered binomial regression. Ecol. Model. 218, 162174 (2008).
  19. Hoegh-Guldberg, O., Ortiz, J. C. & Dove, S. The future of coral reefs. Science 334, 14941495 (2011).
  20. Pandolfi, J. M., Connolly, S. R., Marshall, D. J. & Cohen, A. L. Projecting coral reef futures under global warming and ocean acidification. Science 333, 418422 (2011).
  21. Pandolfi, J. M., Connolly, S. R., Marshall, D. J. & Cohen, A. L. Response to ‘the future of coral reefs’. Science 334 (2011).
  22. Weis, V. M. The susceptibility and resilience of corals to thermal stress: Adaptation, acclimatization or both? Mol. Ecol. 19, 15151517 (2010).
  23. Kleypas, J. A. & Langdon, C. et al. in Coral Reefs and Climate Change: Science and Management Vol. 61 (ed. Phinney, J. T.) 73110 (AGU Monograph Series, Coastal and Estuarine Studies, Geophys. Union, 2006).
  24. Langdon, C. & Atkinson, M. J. Effect of elevated pCO2 on photosynthesis and calcification of corals and interactions with seasonal change in temperature/irradiance and nutrient enrichment. J. Geophys. Res. 110, C09S07 (2005).
  25. Schneider, K. & Erez, J. The effect of carbonate chemistry on calcification and photosynthesis in the hermatypic coral Acropora eurystoma. Limnol. Oceanogr. 51, 12841293 (2006).
  26. Ohde, S. & van Woesik, R. Carbon dioxide flux and metabolic processes of coral reefs, Okinawa. Bull. Mar. Sci. 65, 559576 (1999).
  27. Silverman, J., Lazar, B., Cao, L., Caldeira, K. & Erez, J. Coral reefs may start dissolving when atmospheric CO2 doubles. Geophys. Res. Lett. 36, L05606 (2009).
  28. Silverman, J., Lazar, B. & Erez, J. Effect of aragonite saturation, temperature, and nutrients on the community calcification rate of a coral reef. J. Geophys. Res. 112, C05004 (2007).
  29. Cohen, A. L., McCorkle, D. C., de Putron, S. J., Gaetani, G. A. & Rose, K. A. Morphological and compositional changes in the skeletons of new coral recruits reared in acidified seawater: Insights into the biomineralization response to ocean acidification. Geochem. Geophys. Geosyst. 10 (2009).
  30. Anthony, K. R. N., Kline, D. I., Diaz-Pulido, G., Dove, S. & Hoegh-Guldberg, O. Ocean acidification causes bleaching and productivity loss in coral reef builders. Proc. Natl Acad. Sci. USA 105, 1744217446 (2008).
  31. Wooldridge, S. A. A new conceptual model for the warm-water breakdown of the coral–algae endosymbiosis. Mar. Freshwat. Res. 60, 483496 (2009).
  32. Hoegh-Guldberg, O. & Jones, R. J. Photoinhibition and photoprotection in symbiotic dinoflagellates from reef-building corals. Mar. Ecol. Prog. Ser. 183, 7386 (1999).
  33. UNFCCC The Cancun Agreements: Outcome of the Work of the Ad Hoc Working Group on Long-term Cooperative Action Under the Convention FCCC/CP/2010/7/Add.1. (UNFCCC, 2010); available via
  34. Buddemeier, R. W., Lane, D. R. & Martinich, J. A. Modeling regional coral reef responses to global warming and changes in ocean chemistry: Caribbean case study. Climatic Change 109, 375397 (2011).
  35. Meinshausen, M. et al. Greenhouse-gas emission targets for limiting global warming to 2°C. Nature 458, 1158 (2009).
  36. Mumby, P. J., Hastings, A. & Edwards, H. J. Thresholds and the resilience of Caribbean coral reefs. Nature 450 (2007).
  37. Hoegh-Guldberg, O. Climate change, coral bleaching and the future of the world’s coral reefs. Mar. Freshwat. Res. 50, 839866 (1999).
  38. Jansen, E. & Overpeck, J. in IPCC Climate Change 2007: The Physical Science Basis (eds Solomon, S. et al.) 433498 (Cambridge Univ. Press, 2007).
  39. Caldeira, K. & Wickett, M. E. Ocean model predictions of chemistry changes from carbon dioxide emissions to the atmosphere and ocean. J. Geophys. Res. 110, C09S04 (2005).

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Author information


  1. Earth System Analysis, Potsdam Institute for Climate Impact Research, 14412 Potsdam, Germany

    • K. Frieler,
    • M. Meinshausen,
    • A. Golly,
    • M. Mengel &
    • K. Lebek
  2. School of Earth Sciences, University of Melbourne, Victoria 3010, Australia

    • M. Meinshausen
  3. Department of Geography, University of British Columbia, Vancouver V6T 1Z2, Canada

    • S. D. Donner
  4. Global Change Institute and ARC Centre for Excellence in Coral Reefs, University of Queensland, St Lucia, Brisbane, Queensland 4072, Australia

    • O. Hoegh-Guldberg


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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