January 1, 2018

Impacts of Climate Change on World Heritage Coral Reefs: Update to the First Global Scientific Assessment

Publisher: United Nations Educational, Scientific and Cultural Organization (UNESCO)

Funders: United States National Oceanic and Atmospheric Administration, University of Colorado, University of Miami

Authors: Ruben van Hooidonk, Scott F. Heron

Language: English

In 2017, UNESCO's World Heritage Centre published the first global scientific assessment of the impact of climate change on UNESCO World Heritage coral reefs. The 'Assessment' reported that heat stress events have increasingly caused severe coral bleaching and mortality of World Heritage-listed reefs around the world over the past three decades. Of the 29 World Heritage listed natural coral reef properties (Fig. 1), 15 were exposed to repeated severe heat stress during the 2014-2017 global bleaching event. Recurrent severe bleaching was already apparent at more than half of the properties. While this global event did not trigger the onset of annual severe bleaching conditions in perpetuity, the impact of recurrent bleaching on coral reefs was clearly demonstrated. The Assessment revealed that 25 of the 29 World Heritage reefs are projected to severely bleach twice-per-decade by 2040 under a business-as-usual CO2 emissions scenario (RCP8.5, where emissions and temperature continue to rise through the 21st century). Under the RCP4.5 scenario, in which emissions peak around 2040 and then decline, the proportion of World Heritage-listed reefs exposed to twice-per-decade severe bleaching by 2040 was dramatically reduced to less than half (14) of the reef properties.

The first global assessment was released ahead of the 41st session of the World Heritage Committee in 2017 and underpinned the first decision of the Committee on coral reefs and climate change: to reiterate "the importance of States Parties undertaking the most ambitious implementation of the Paris Agreement of the UNFCCC [United Nations Framework Convention on Climate Change]", and to strongly invite all States Parties "to undertake actions to address Climate Change under the Paris Agreement consistent with their common but differentiated responsibilities and respective capabilities, in the light of different national circumstances that are fully consistent with their obligations within the World Heritage Convention to protect the OUV [Outstanding Universal Value] of all World Heritage properties" (Decision 41 COM 7).

This update responds to the recommendation of the Assessment to undertake high-resolution future projection analysis under the RCP2.6 emissions scenario, in which emissions peak during the current decade (2010-2020) and achieve the limit of well below 2°C by 2100. This update further responds to the World Heritage Committee request to make available the most current knowledge regarding the impacts of climate change on World Heritage properties. This updated analysis provides understanding of the implications of meeting the long-term goal of the UNFCCC Paris Agreement for World Heritage-listed coral reefs.