A recent report published by the United Nations Environment Programme (UNEP) in November 2020 has warned that the world is at serious risk of losing coral reefs by the end of the century. Coral reef ecosystems provide food and livelihoods to millions of people around the world. Despite only covering around 2% of the Earth’s surface, they sustain more than a quarter of all aquatic species. Coral reefs also help defend cities and coastlines from natural disasters through flood mitigation. With so much to lose, if immediate action is not taken, these valuable ecosystems could be lost forever.

What Is Happening To Coral Reefs?

Coral reefs are essential to a wide range of aquatic species. They also defend coastlines from wave and storm flooding, absorb harmful carbon from the atmosphere and help to recycle nutrients. Their extinction will have devastating effects not only for marine life, but also for more than a billion people worldwide who rely directly or indirectly on these ecosystems across the world.

Due to global warming, sea surface temperatures are warming. These warmer waters result in a stress response which causes them to bleach. Coral bleaching is the process where corals expel the algae that live inside their tissues, known as zooxanthellae, that provide the coral with up to 90% of their energy. This results in the coral losing its coloration and they will appear white. Whilst the coral is not dead at this point, it makes them extremely vulnerable to coral death. Corals can survive short-term disturbances, but if the conditions that lead to the expulsion of the zooxanthellae persist, the corals are likely to die. Coral bleaching events are becoming more widespread, frequent, severe and lasting for longer.

In 2014, scientists bore witness to the Third Global Bleaching Event that lasted over 36 months. This was the longest coral bleaching event on record, as well as the pervasive and destructive. Coral reefs across the Pacific, Indian and Atlantic oceans were all impacted and experienced coral bleaching to a degree.

In addition to coral bleaching, corals are also threatened with a bigger threat known as marine heatwaves, according to a study published in Current Biology. Due to a rapidly warming climate, marine heatwaves have recently become a more frequent threat to coral reefs, biologically distinct in its effects on corals. In fact, scientists have found that marine heatwave events are more deadly as they result in immediate heat-induced coral mortality. The most severe marine heatwave was recorded in 2016 across the Great Barrier Reef.

Across the world reefs remain in hot water, with no indication of respite to promote coral recovery from these dramatic events. Whilst corals can recover from bleaching if conditions improve, this seems unlikely given that warming events are getting progressively more intense. There are fears among the scientific community that these events may weaken reefs beyond repair. If coral bleaching events and marine heatwaves become annual occurrences, it would likely lead to ecological collapse of coral reefs as the ecosystems would be too compromised in their ability to supply ecosystem services, including food, coastal protection, medicines and recreation opportunities. 

How Realistic Is It That All Corals Could Be Lost?

In UNEP’s latest report Projections of Future Coral Bleaching Conditions, released in November 2020, the clear links between a rapidly changing climate due to global warming and coral bleaching were laid out. In all likelihood, there are likely two climate-based scenarios: 1) a “worst-case” scenario where the global economy continues to be heavily driven by fossil fuels; and 2) a “middle-of-the-road” scenario, which predicts the likely impact on our climate if countries meet or exceed their current pledges under the Paris Agreement to cut carbon emissions by 50%. 

Under the worst case and fossil-fuel-led scenario, the UNEP report estimates that by 2100 every coral reef throughout the world will bleach. It is also predicted that by 2034, severe bleaching events will become an annual occurrence. Worryingly, this annual bleaching estimate has moved 9 years sooner than it was estimated in UNEP’s report published 3 years ago. What is likely to happen under the “middle-of-the-road” scenario? According to the report, severe annual bleaching events could be delayed by approximately eleven years, to 2045.

In areas where bleaching is already common, scientists predict that these reefs will be dubbed as ‘climate losers’ and by 2030 will be experiencing serious and severe bleaching above the global average. Widespread bleaching is already a common occurrence in many countries, including Fiji, Papua New Guinea, New Caledonia, Saudi Arabia and eastern Australia. Other reefs throughout western Australia, the Bahamas, Indonesia, India, Madagascar and Malaysia, are less at risk from severe bleaching. These reefs are less vulnerable to bleaching and could provide a refugium for coral populations. However, this too is likely only to be temporary, with the report predicting that these reefs too will begin bleaching around 2044.

What Needs To Be Done To Save Coral Reefs?

A changing climate is natural to a degree, and corals have proven to be adaptable to this change over their millions of years in existence. This tenacious capacity does provide some hope. The UNEP report does explore the possibility of corals adapting to warming sea surface temperatures and becoming less vulnerable to bleaching as a result. It is estimated that for every 0.25 °C of warming corals adapt to, this may delay the point of annual bleaching by up to 7 years. In the scenario that corals could adapt to 1 °C of warming, that would provide at least 25 years reprieve from annual bleaching events 

However, if current greenhouse gas emissions continue at their current rate (and are in fact predicted to increase), corals would not survive even if they were capable of adapting to 2°C of ocean warming. In essence, if the international community fails to commit to and deliver dramatic declines in the global production of greenhouse gases, it is incredibly likely that coral reef ecosystems throughout the world will be lost to coral bleaching. 

The Climate Change Performance Index, which assesses the climate protection performance of the 57 countries responsible for 90% of the world’s carbon dioxide emissions, recently found that none of the countries that committed to the Paris Agreement have implemented the policies needed to meet their pledged emission reduction targets. However, in 2020 over 110 countries made new pledges to transition to a carbon-neutral economy by 2050. Importantly, major emitters such as the European Union, Japan, South Korea and the United Kingdom made these carbon-neutral commitments. The United States is also set to rejoin the Paris Agreement, aiming to be carbon-neutral by 2050. So there is hope for greenhouse gas emissions to be curbed.

Coral reefs also need investment. In February 2018, figures were released on the international financial support that has been received to protect and sustainably manage the world’s coral reefs. Not only is the funding inadequate, it also undervalues these crucial yet fragile ecosystems that provide us with food, livelihoods, medicine and environmental protection. As evidenced by initiatives such as Green Fins, there are many benefits from investing in protecting coral reefs that through effective changes to business practices can lead to economic, environmental and social benefits.