Section 4 - Case Study 03

Risk assessment • Warm-water coral reefs are vital to the wellbeing of up to a billion people and almost a million species. • Globally, coral reefs are experiencing unprecedented mortality under repeated mass bleaching events, highlighting the impact that global warming (interacting with other, predominantly humandriven environmental stressors) is already having. • The central estimate of the thermal tipping point for warm-water coral reefs of 1.2°C global surface warming above pre-industrial is already exceeded and without stringent climate mitigation their upper thermal threshold of 1.5°C may be reached within the next 10 years, degrading reef functioning and provision of ecosystem services to millions of people. • Even under the most optimistic current emission scenarios of stabilising warming at 1.5°C without any overshoot, it is considered that warm-water coral reefs are virtually certain (>99% probability) to tip, given the upper range of their thermal tipping point is 1.5°C. • The goal of the Paris Agreement to limit global warming “well below 2°C” (ie. 1.5°C) will not prevent coral reefs from irreversibly passing their thermal tipping point. Recommendations • Stringent emission mitigation and enhanced removals are needed to return to a global mean surface warming below 1.2°C with a minimal overshoot period and eventually returning to 1°C above preindustrial. These temperatures are essential for retaining functional warm-water coral reefs at meaningful scale. • Minimising non-climatic stressors, particularly by improving reef management, can give reefs the best chance of surviving under what must be a minimal temperature exceedance from their tipping point threshold. • Urgent policy and societal responses are needed to address the ecosystem and livelihood impacts of degraded or non-functional reefs. Regional risk assessments that investigate the impacts must be produced.

PEARCE-KELLY Paul;  YESSON Chris;  MCFIELD Melanie;  MUÑIZ-CASTILLO Aarón Israel;  SOTO Melina;  ARIAS-GONZALEZ Jesus Ernesto;  MORGAN Kyle;  BILL-WEILANDT Alina;  KJERFVE Björn;  CORNWALL Christopher E.;  ALVAREZ-FILIP Lorenzo;  MILKOREIT Manjana;  LENTON Tim;  ROMAN Rosa; 

2025-11-18

University of Exeter

JRC143928

https://global-tipping-points.org/download/1418/,    global-tipping-points.org,    https://publications.jrc.ec.europa.eu/repository/handle/JRC143928,