UN report: World could lose coral reefs by end of century

Coral bleaching on Australia's Great Barrier Reef: after (left) and before (right). - Photo: The Ocean Agency/WL Catlin Seaview via UNEP |

According to a recent United Nations Environmental Programme report, reefs worldwide are in danger of vanishing by the end of this century, under the pressures of ocean warming and coral bleaching.

“In the face of inaction, coral reefs will soon disappear,” Leticia Carvalho, head of the United Nations Environmental Programme’s Marine and Freshwater Branch, said following  the issuing of the report in late December.

“Humanity must act with evidence-based urgency, ambition and innovation to change the trajectory for this ecosystem, which is the canary in the coalmine for climate’s impact on oceans, before it’s too late,” she said in a press release accompanying the report.

The latest report is a follow-up to a study that looked at the longest global coral-bleaching event on record, from 2014 to 2017. That event impacted the Atlantic, Pacific and Indian oceans.

The report states, “The length of the event [meant] corals in some parts of the world had no time to recover in 2014, 2015 or 2016 during the cool/winter season, prior to experiencing bleaching the following year. This recent global bleaching event of 2014-2017 represents what climate model projections presented in this report suggest may become the norm over the coming two decades.”

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The latest report updates the 2017 study with projections of the timing of severe coral-bleaching conditions at coral reef locations around the world, using a new generation of climate models employed by the Intergovernmental Panel on Climate Change.

Using this model, the report calculates that Cayman’s reefs could be experiencing annual severe bleaching by 2035.

The report outlined the projected year by which sea temperature stress on coral reefs in specific locations is expected to be severe enough to cause bleaching annually. At this point, reefs are certain to change and recovery will be very limited.


Coral bleaching occurs when corals react to rising water temperatures by expelling the microscopic algae living in their tissues.

Although the affected coral may appear white and lifeless at this point, it is still alive and can recover its algae if conditions improve and the water temperature drops. However, the UN report points out that the loss of the algae puts the coral under increased stress, and if the bleaching persists, the coral will die.

With prolonged bleaching that continues over several years, the corals have no opportunity to recover.

What can be done?

The latest report offers two possible scenarios of what happens next – a ‘worst-case’ one involving continued global use and dependence on fossil fuels, and a ‘middle-of-the-road’ one in which countries exceed their current pledges to cut back on fossil fuels and limit carbon emissions by 50%.

Under the ‘worst-case’ scenario, the report estimates that all of the world’s reefs will bleach by the end of the century, with annual severe bleaching occurring on average by 2034, nine years ahead of predictions published three years ago.

If jurisdictions do manage to achieve the ‘middle-of-the-road’ scenario, severe bleaching could be delayed by 11 years, to 2045, the UNEP report projected.

In a statement, the report’s lead author Ruben van Hooidonk, who is a coral researcher with the US National Oceanic and Atmospheric Administration, said, “The sad part is that the projections are even more dire than before.”

He added, “It means we really need to try to reduce our carbon emissions to save these reefs. This report shows that we need to do it even more urgently and take more action because it’s even worse than what we thought.”

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