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Safe havens for coral reefs will be almost non-existent at 1.5°C of global warming – new study

Safe havens for coral reefs will be almost non-existent at 1.5°C of global warming – new study

A boulder coral on a reef that has bleached white.

Coral reefs are a source of life. Long time ago, it was regarded as a valuable resource.As one of the most important ecological casualties of global heating. In New research published in the journal PLOS Climate, we found that the future of these tropical ecosystems – thought to harbour There are more species than any other – is probably worse than anticipated.

Climate change is making it more common. Marine heatwaves worldwide. Corals have adapted to live in a specific temperature range, so when ocean temperatures are too hot for a prolonged period, corals can bleach – losing the colourful algae that live within their tissue and nourish them via photosynthesis – and may eventually die.

In the tropics Mass bleaching and death-offsAs the climate has warmed, they have become more common than ever. Corals are now more vulnerable to heatwaves, which means that they have less time to recover.

A boulder coral on a reef that has bleached white.
The corals that are bleached are more susceptible to disease and starvation.
Maria Beger, Author provided

In a 2018 report, the Intergovernmental Panel on Climate Change predicted that 1.5°C of global warming would cause Between 70 and 90% of the world’s coral reefs to disappear. Now, with models capable of examining temperature differences between coral reefs one kilometre apart, our team found that at 1.5°C of warming, which the world is predicted to reach in the Early 2030s without drastic action to limit greenhouse gas emissions, 99% of the world’s reefs will experience heatwaves that are too frequent for them to recover.

It would spell disaster for the thousands of coral reef-dependent species, as well the roughly One billion peopleCoral reef biodiversity has a positive impact on the livelihoods of people who rely on it for their food supply.

Thermal refugia

Corals can be affected by the thermal stress of a heatwave. Huge geographic area, such as the entire northern Great Barrier Reef and archipelagos of the Maldives. A marine heatwave in 2015-16 This bleaching has caused widespread damageEach of the Pacific, Atlantic, or Indian Oceans.

Corals are small polyp-like creatures that form colonies of thousands. They secrete a calcium carbonate bone skeleton which creates a reef. Overfishing and pollution can slow down coral growth and make it difficult for them to recover from bleaching and die-offs. Some species grow faster and can recover quicker.

Scientists hope so Local conditionsYou can also find reef tracts that will provide you with guaranteed safety. Temperatures suitableCorals will continue to thrive in warmer areas. These conditions could be possible because of upwelling, which brings cooler water to the surface or strong ocean currents. Managers of reefs can PrioritizeThese so-called refugia offer corals greater survival chances.

A sunlit coral reef populated by lots of tropical fish.
Healthy reefs can support a wide variety of life.
Maarten De Brauwer, Author provided

These refugia can be difficult to find because they are likely small and the resolutions of climate projections that model changes over time in ocean temperatures tend to be too poor. Our team improved the resolution of climate model projections through downscaling them using historical satellite observations to determine where refugia will persist in the future.

We found that, from 1986 to 2019, 84% of the world’s reefs offered sufficient thermal refuge. This meant corals had enough recovery time between bleaching events. With 1.5°C of global warming above pre-industrial levels, only 0.2% of these refugia remain. At 2°C of warming, safe havens from heat for coral reefs will no longer exist.

Two world maps comparing coral reef refugia 1986-2019 versus at 1.5°C.

Most of the world’s reef refugia disappear at 1.5°C.
Dixon et al. (2022)/PLOS Climate, Author provided

Preliminary findings from another study (yet to complete the peer-review process) would seem to confirm the catastrophic effects of 1.5°C of global warming on coral reefs. Scientists in the US carried out this research independently using a different method, but the same climate models.

Future of coral reefs

Global warming of 1.5°C is the lower limit that world leaders aspired to maintain when they signed the Paris agreement in 2015. This target is moving Further out of reach. There is no safe limit on global warming for coral reefs. Given the rate at which the global average temperature is increasing, marine heatwaves are likely to become so frequent that most of the world’s coral reefs will experience intolerable heat stress regularly. Most reefs have experienced at least one of these events in the past decade.

Not all regions are affected by heatwaves at the same time. Corals also do not bleach equally. Some coral speciesThey are more capable of dealing with extreme temperatures than other people because they have higher levels of resilience. Growth is a form ofOr the Types of algaeWithin their tissue. Nevertheless, even coral species that are resistant to heatwaves will likely be affected by the frequency and magnitude of these heatwaves, indicating that the world will lose the majority of its reef biodiversity. Future coral reefs will be very different from the diverse and colourful ecosystems we have today.

An underwater field of coral rubble smothered in algae.
A dead coral reef.
Rich Carey/Shutterstock

Already, climate change is underway Degrading coral reefs worldwide. We now know that protecting the last temperature refuges won’t work by itself. The best way to save what is left is to reduce greenhouse gas emissions in the next decade.

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