UNESCO REPORT - "Assessment: World Heritage coral reefs likely to disappear by 2100 unless CO2 emissions drastically reduce"

Excerpts from United Nations Education, Scientific and Cultural Organisation (UNESCO), Impacts of Climate Change on World Heritage Coral Reefs: A First Global Scientific Assessment, 23 June 2017:

Seventy two percent of World Heritage reef properties (21 of 29) have been exposed to severe and/or repeated heat stress during the past three years. Within the three years of the current global bleaching event (mid 2014-mid 2017), 18 World Heritage reefs (62%) were in the highest impact category (dark red) at either one or both stress levels (Table 1c,d). A further three properties were exposed to recurrent bleaching stress (red) or a single severe stress event (orange). This illustrates the dramatic impact on coral reefs during this period, which has seen three consecutive years of record global temperature (2014, 2015 and 2016), and reflects an increase in bleaching frequency from that seen in the prior decades. Only four properties (14%) escaped bleaching-level heat stress during this three-year bleaching event: Brazilian Atlantic Islands (Brazil), iSimangaliso Wetland Park (South Africa), Sanganeb Marine National Park and Dungonab Bay – Mukkawar Island Marine National Park (Sudan) and Socotra Archipelago (Yemen)…..

Coral mortality during the third global bleaching event has been among the worst ever observed, including at World Heritage reefs; e.g., Great Barrier Reef (Australia), Papahānaumokuākea (USA) and Aldabra Atoll (Seychelles)…..

Papahānaumokuākea (USA) and the Great Barrier Reef (Australia), among the most spatially vast of all World Heritage properties…..

Coral communities typically take at least 15 to 25 years to recover from mass mortality events such as destructive cyclones and mass bleaching events. If the frequency of mass mortality events increases to a point where the return time of mortality events is less than the time it takes to recover, the abundance of corals on reefs will decline. Consequently, the frequency of stress events that reached or exceeded the 4°C and 8°C-week DHW thresholds was calculated for each World Heritage reef-containing property (Table 1) to detect if the bleaching frequency exceeded the best-case rates of recovery.

This analysis showed that World Heritage properties containing coral reefs have been increasingly exposed to heat stress during recent years. Nearly half (13) of the 29 World Heritage Listed reef properties were exposed to levels of heat stress that cause coral bleaching, on average, more than twice per decade during the 1985- 2013 period

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