Past the Precipice? Projected Coral Habitability Under Global Heating.

Area of Science:

• Marine biology
• Climate science
• Oceanography

Background:

• Coral reefs are declining globally due to environmental stressors and climate change.
• Ocean warming, specifically increased sea surface temperatures (SSTs), is a primary threat causing coral bleaching and mortality.

Purpose of the Study:

• To project future thermal conditions for coral reefs at a 1 km resolution.
• To assess the recurrence of severe bleaching events under various climate emissions scenarios.
• To inform conservation strategies by identifying potential reef refugia.

Main Methods:

• Utilized high-resolution (1 km) SST observations and CMIP6 model data.
• Employed a novel statistical downscaling method for improved accuracy, especially near coastlines.
• Calculated Thermal Departure (TD) metrics, including TD5Y (5-year bleaching recurrence) and TD10Y (10-year bleaching recurrence).

Main Results:

• As of 2021, over 91% and 79% of reefs have already exceeded TD10Y and TD5Y, respectively.
• Under moderate to high emissions scenarios (SSP2-4.5, SSP3-7.0, SSP5-8.5), 99% of reefs are projected to exceed TD5Y by 2040.
• At 1.5°C global warming, 2-5% of reefs may remain below TD5Y; at 2.0°C, none will.

Conclusions:

• Widespread, long-term coral reef degradation is likely unavoidable without drastic emissions cuts.
• Urgent greenhouse gas emission reductions are critical for coral reef survival.
• Improved ecological projection models are essential for identifying refugia and guiding conservation for climate-vulnerable ecosystems.