Ocean warming is increasing the incidence, scale, and severity of global-scale coral bleaching and mortality, culminating in the third global coral bleaching event that occurred during record marine heatwaves of 2014-2017.

While local effects of these events have been widely reported, the global implications remain unknown.

Analysis of 15,066 reef surveys during 2014-2017 revealed that 80% of surveyed reefs experienced significant coral bleaching and 35% experienced significant coral mortality.

The global extent of significant coral bleaching and mortality was assessed by extrapolating results from reef surveys using comprehensive remote-sensing data of regional heat stress.

This model predicted that 51% of the world’s coral reefs suffered significant bleaching and 15% significant mortality, surpassing damage from any prior global bleaching event.

These observations demonstrate that global warming’s widespread damage to coral reefs is accelerating and underscores the threat anthropogenic climate change poses for the irreversible transformation of these essential ecosystems.

2014-17 Global Coral Bleaching Event: The Most Severe and Widespread Coral Reef Destruction

The dramatic increase in marine heatwaves has exposed coral reef ecosystems to more frequent, more intense, and longer-lasting heat stress [1-4]. These are predicted to accelerate in the future [5-7], making anthropogenic climate change the foremost threat to coral reefs globally [1, 2, 5, 8-10].

Strong marine heatwaves cause mass-bleaching of corals, which occurs when the relationship between corals and their photosynthetic symbionts breaks down[11]. Bleached corals are physiologically damaged, nutritionally compromised, and can die if the bleaching is severe or prolonged.

During what were then the four warmest years on record, [12-14], reefs around the world experienced the third global-scale coral bleaching event (GCBE3) [15, 16] that lasted from June 2014 to May 2017 (hereafter referred to as 2014- 17).

This was the most severe global heat stress event recorded on coral reef ecosystems [1, 3, 15], even stronger than the two prior global bleaching events recorded in 1998 [17] and 2010 [2, 18].

Moreover, this was the first time that a global bleaching event lasted longer than a single year [1, 3, 15] – this one spanning three years with bleaching at some locations continuing after the global event concluded [19-21].

Numerous studies have revealed how GCBE3 has impacted coral reefs locally at sites around the globe, including several showing the most severe impacts on record in many locations (see [22] and references therein).

This paper provides the first global-scale analysis of the heat stress affecting coral reefs during 2014-17 and the resultant bleaching and mortality observed.

We derive statistical relationships between global-scale, remotely-sensed heat stress and onsite surveys of coral bleaching and mortality and use these to estimate the impact of GCBE3, accounting for regional and inter-annual differences in bleaching and mortality responses.

Figure 5 Percentage of global reef pixels reaching DHW greater than 4 and 8C-weeks
Figure 5 Percentage of global reef pixels reaching DHW greater than 4 and 8C-weeks
  • April 2022
Scroll to Top