Letter | Published:

Coral bleaching under unconventional scenarios of climate warming and ocean acidification

Nature Climate Change volume 5, pages 777781 (2015) | Download Citation


Elevated sea surface temperatures have been shown to cause mass coral bleaching1,2,3. Widespread bleaching, affecting >90% of global coral reefs and causing coral degradation, has been projected to occur by 2050 under all climate forcing pathways adopted by the IPCC for use within the Fifth Assessment Report4,5. These pathways include an extremely ambitious pathway aimed to limit global mean temperature rise to 2 °C (ref. 6; Representative Concentration Pathway 2.6—RCP2.6), which assumes full participation in emissions reductions by all countries, and even the possibility of negative emissions7. The conclusions drawn from this body of work, which applied widely used algorithms to estimate coral bleaching8, are that we must either accept that the loss of a large percentage of the world’s coral reefs is inevitable, or consider technological solutions to buy those reefs time until atmospheric CO2 concentrations can be reduced. Here we analyse the potential for geoengineering, through stratospheric aerosol-based solar radiation management (SRM), to reduce the extent of global coral bleaching relative to ambitious climate mitigation. Exploring the common criticism of geoengineering—that ocean acidification and its impacts will continue unabated—we focus on the sensitivity of results to the aragonite saturation state dependence of bleaching. We do not, however, address the additional detrimental impacts of ocean acidification on processes such as coral calcification9,10 that will further determine the benefit to corals of any SRM-based scenario. Despite the sensitivity of thermal bleaching thresholds to ocean acidification being uncertain11,12, stabilizing radiative forcing at 2020 levels through SRM reduces the risk of global bleaching relative to RCP2.6 under all acidification–bleaching relationships analysed.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.


  1. 1.

    Coral bleaching: Causes and consequences. Coral Reefs 16, S129–S138 (1997).

  2. 2.

    et al. Coral bleaching and mortality on artificial and natural reefs in Maldives in 1998, sea surface temperature anomalies and initial recovery. Mar. Pollut. Bull. 42, 7–15 (2001).

  3. 3.

    Climate change, coral bleaching and the future of the world’s coral reefs. Mar. Freshwat. Res. 50, 839–866 (1999).

  4. 4.

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

  5. 5.

    , & Temporary refugia for coral reefs in a warming world. Nature Clim. Change 3, 508–511 (2013).

  6. 6.

    et al. The representative concentration pathways: An overview. Climatic Change 109, 5–31 (2011).

  7. 7.

    et al. Twenty-first-century compatible CO2 emissions and airborne fraction simulated by CMIP5 earth system models under four representative concentration pathways. J. Clim. 26, 4398–4413 (2013).

  8. 8.

    , , & NOAA’s Coral Reef Watch program from satellite observations. Ann. GIS 17, 83–92 (2011).

  9. 9.

    & 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).

  10. 10.

    & Sensitivity of coral calcification to ocean acidification: A meta-analysis. Glob. Change Biol. 19, 282–290 (2013).

  11. 11.

    , , , & Ocean acidification causes bleaching and productivity loss in coral reef builders. Proc. Natl Acad. Sci. USA 105, 17442–17446 (2008).

  12. 12.

    , & Ocean acidification has no effect on thermal bleaching in the coral Seriatopora caliendrum. Coral Reefs 33, 119–130 (2013).

  13. 13.

    & Ecological goods and services of coral reef ecosystems. Ecol. Econ. 29, 215–233 (1999).

  14. 14.

    , & Multiple scattering on coral skeletons enhances light absorption by symbiotic algae. Limnol. Oceanogr. 50, 1025–1032 (2005).

  15. 15.

    et al. An overview of geoengineering of climate using stratospheric sulphate aerosols. Phil. Trans. R. Soc. Math. A 366, 4007–4037 (2008).

  16. 16.

    et al. Caribbean coral growth influenced by anthropogenic aerosol emissions. Nature Geosci. 6, 362–366 (2013).

  17. 17.

    , , & Risks to coral reefs from ocean carbonate chemistry changes in recent earth system model projections. Environ. Res. Lett. 8, 034003 (2013).

  18. 18.

    & Consequences of ecological, evolutionary and biogeochemical uncertainty for coral reef responses to climatic stress. Curr. Biol. 24, R413–R423 (2014).

  19. 19.

    et al. Development and evaluation of an Earth-system model—HadGEM2. Geosci. Mod. Dev. Discuss. 4, 997–1062 (2011).

  20. 20.

    et al. The geoengineering model intercomparison project (GeoMIP). Atmos. Sci. Lett. 12, 162–167 (2011).

  21. 21.

    , , , & Global disparity in the ecological benefits of reducing carbon emissions for coral reefs. Nature Clim. Change 4, 1090–1094 (2014).

  22. 22.

    , , & What spatial scales are believable for climate model projections of sea surface temperature? Clim. Dynam. 43, 1483–1496 (2014).

  23. 23.

    Coping with commitment: Projected thermal stress on coral reefs under different future scenarios. PLoS ONE 4, e5712 (2009).

  24. 24.

    , , , & Tropical coral reef habitat in a geoengineered, high-CO2 world. Geophys. Res. Lett. 40, 1799–1805 (2013).

  25. 25.

    et al. Avoiding coral reef functional collapse requires local and global action. Curr. Biol. 23, 912–918 (2013).

  26. 26.

    , , , & Coral reefs may start dissolving when atmospheric CO2 doubles. Geophys. Res. Lett. 36, L05606 (2009).

  27. 27.

    , , & Coral resilience to ocean acidification and global warming through pH up-regulation. Nature Clim. Change 2, 623–627 (2012).

  28. 28.

    , , & Response of ocean acidification to a gradual increase and decrease of atmospheric CO2. Environ. Res. Lett. 9, 024012 (2014).

Download references


We thank J. Orr, D. Long and I. Chollett for assistance with data processing. The study was financially supported by a NERC grant to P.J.M. and P.C., the University of Exeter, and the EU FORCE project and was supported by the Joint DECC/Defra Met Office Hadley Centre Climate Programme.

Author information


  1. College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter EX4 4QF, UK

    • Lester Kwiatkowski
    •  & Peter Cox
  2. Department of Global Ecology, Carnegie Institution for Science, 260 Panama Street, Stanford, California 94305, USA

    • Lester Kwiatkowski
  3. College of Life and Environmental Sciences, University of Exeter, Exeter EX4 4RJ, UK

    • Paul R. Halloran
  4. Marine Spatial Ecology Lab, School of Biological Sciences, University of Queensland, St Lucia Brisbane, Queensland 4072, Australia

    • Peter J. Mumby
  5. Hadley Centre, Met Office, Exeter, EX1 3PB, UK

    • Andy J. Wiltshire


  1. Search for Lester Kwiatkowski in:

  2. Search for Peter Cox in:

  3. Search for Paul R. Halloran in:

  4. Search for Peter J. Mumby in:

  5. Search for Andy J. Wiltshire in:


L.K., P.C. and P.R.H. designed and conducted the research and analysis. A.J.W. and P.R.H. performed the HadGEM2-ES simulations. L.K., P.C., P.R.H., A.J.W. and P.J.M. wrote the paper.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Lester Kwiatkowski.

Supplementary information

About this article

Publication history






Further reading