The silent ocean killer set to harm '1 billion people'

Heat stress could overwhelm almost all of the world’s coral reefs if temperatures continue to rise as predicted, Australian scientist warn.

Even if global warming is capped at 1.5 degrees above pre-industrial levels, just 0.2 per cent of coral landscapes will likely remain unaffected.

At 2 degrees, around 100 per cent of reefs may be impacted by bleaching.

Left - A school of fish. Right - The coastal prefecture of Okinawa.
Reefs are estimated to support 1 billion people and a quarter of the world's marine fish species. Source: Getty - File

Estimates suggest the world has warmed by 1.1 degrees and approximately 84 per cent of reefs have been harmed by rising temperatures.

The outcome of further heat stress “will be catastrophic”, a James Cook University study published in the journal PLOS Climate concluded.

With reefs sheltering around one quarter of all marine fish species, and essential to the lives of between 500 million and 1 billion people, their loss could be dire.

An author of the study, Associate Professor Scott Heron, told Yahoo News Australia there is potential for many people to lose the fish they rely upon for food.

“There's also other services like tourism and recreation that are a part of what coral reefs give to human communities,” he said.

“There’ll be a big potential impact on real people if we are to lose functioning coral reef ecosystems.”

Climate change will create cascading impact as reefs die

As climate change worsens, extreme weather will become more severe.

If protection provided by reefs declines due to coral die-offs then coastlines will face greater repercussions from these events.

This charts shows how coral reefs will be affected by rising temperatures. Source: PLOS Climate
This charts shows how coral reefs will be affected by rising temperatures. Source: PLOS Climate

“If and when a tsunami occurs, the impact that it could have when there's no longer a reef to protect the coastline would be greater,” Assoc Prof Heron said.

“The same is true for storm damage.

“When we get storm surges associated with cyclone events, or waves associated with king tide events, then there is the potential for greater impacts resulting from those.”

Key stories about the Great Barrier Reef

'It will snap': Reef systems stretched like elastic bands

Corals have adapted to thrive in certain temperatures, but when the climate changes they become stressed.

If heating occurs for an extended period, corals will often bleach and this can result in death.

The new study suggests that at 2 degrees of warming, corals all around the world will be exposed to heat stress more than once every five years, resulting in what Assoc Prof Heron calls a “problematic” outcome.

A person diving amongst bleached coral.
Coral bleaching is affecting 84 per cent of the world's coral reefs. Source: Getty

“I liken it to stretching an elastic band,” he said.

“You can stretch it, it comes back, you can stretch it again, it comes back.

“At some point, if you stretch it too far it will snap, and there's concern that we may be stretching coals too far, so that they snap.”

'Is this the end of the story?': Hope remains

Despite their dark predictions, researchers hold out hope that some coral systems may survive.

Some small bioregions in Indonesia, the eastern South Pacific, French Polynesia, Eastern Pacific and Tropical Pacific could be less affected by a 2 degree temperature rise.

It’s a characteristic of a number of reefs to experience fluctuations in temperature variability and they have potential to cope with heat stress better than other systems.

These regions sadly are “few and far between” and Australia’s Great Barrier Reef is not among them.

To save what remains of the world’s coral, Assoc Prof Heron believes a two-pronged approach is required and this will involve both management of reefs and urgent action to reduce fossil fuel use.

Changes are occurring at such a rapid rate due to the climate crisis that scientists are grappling to keep up.

It remains unknown whether some coral will be able to adapt and repopulate in the future.

“Is this the very end of the story?” Assoc Prof Heron asks.

“I hope not.”

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