Global projections of sea surface temperature and coral bleaching risk in the 21st century

The timing, duration, and severity of marine heatwaves are rapidly changing due to anthropogenic climate change, yet future trends remain uncertain. In coral reef ecosystems, mass coral bleaching events increasingly occur as a result of cumulative heat stress, which is commonly quantified through degree heating weeks (DHW). Here we compiled a daily-resolution dataset charactering sea surface temperatures, anomalies, and the timing, duration, and extent of severe coral bleaching risk from the recent past (1985) to the future (2100) under three Shared Socioeconomic Pathways. We have validated the downscaled, bias-corrected dataset against a remotely sensed dataset of sea surface temperatures and a global dataset of historical coral bleaching events. Our dataset will permit inferences of future timing, duration, and extent of deleterious marine heatwave conditions.

The naming convention for the daily SST datasets is:

model_scenario__qdmCorrected_timeperiod.nc where model is the name of the CMIP6 model, or ens5 for the ensemble; scenario is the name of the scenario (historical, SSP2-4.5, SSP3-7.0, SSP5-8.5); and timeperiod is the temporal span of the file (e.g., 1985-2014).

The monthly summary files share the same naming convention but include an additional qualifier which identifies whether the values are representative of the minimum, mean, or maximum SST values seen within each month. All values are in °C.

The naming convention for the daily DHW is:

model_scenario_DHW_timeperiod.nc where model is the name of the CMIP6 model, or ens5 for the ensemble; scenario is the name of the scenario (SSP2-4.5, SSP3-7.0, SSP5-8.5); and timeperiod is the temporal span of the file (e.g., 1985-2100). Note that due to the nature of the DHW calculation the historical period (1985-2014) is appended to all the SSP outputs.

The naming convention for the summary DHW files is:

model_scenario_timeperiod_DHWSummary.nc where model is the name of the CMIP6 model, or ens5 for the ensemble; scenario is the name of the scenario (SSP2-4.5, SSP3-7.0, SSP5-8.5); and timeperiod is the temporal span of the file (e.g., 1985-2100). Note that due to the nature of the DHW calculation the historical period (1985-2014) is appended to all the SSP outputs.

All gridded files have the following spatial dimensions – 140 x latitude (35°S to 35°N), 720 x longitude (180°E to 180°W). The time period for each file is different. Daily SST data has n days where n is either 10,927 for the historical period (1985-2014) or 31,325 for the future SSP periods (2015-2100). The monthly SST summary files have n months, where n is either 360 for the historical period or 1032 for the future SSP periods. The summary DHW time dimension is dependent on the variable.

Processing code using NCO, CDO, and R, to process the CMIP6 and ESA CCI Analysis SST dataset. The shell scripts in the 01_preprocessing folder all assume the you have sourced and downloaded the appropriate datasets from the Earth System Grid Federation for CMIP6 models, and the ESA Sea Surface Temperature Climate Change Initiative Level 4 analysis data (both open access).

ESGF - https://esgf-node.llnl.gov/search/cmip6/

CCI analysis SST - https://dx.doi.org/10.5285/62c0f97b1eac4e0197a674870afe1ee6

All scripts require the Climate Data Operators software (https://code.mpimet.mpg.de/projects/cdo), NetCDF operators software (https://nco.sourceforge.net/). Additionally, scripts in the 02_analysis and 03_validation folder require R (https://www.r-project.org/) to be installed. Required packages are listed in the scripts.

Project funding was provided by the Australian Research Council, Subak Australia, and the University of Adelaide Environment Institute.