Too Late to Save Most Coral Reefs?

Unless governments adopt much more aggressive targets for cuts in greenhouse gas (GHG) emissions, 70% of coral reefs will suffer long-term damage by 2030, resulting in devastating consequences for biological diversity, the seafood supply and coastline protection, says new research published in Nature.

Coral reefs are vital nurseries and habitats for up to 33% of all oceans species, explains the World Conservation Union. Seafood is a primary source of protein for more than a billion of the poorest people in the world, and reefs are crucial for protecting coastal regions from storms.

Rising ocean temperatures are pushing many fish into deeper and colder waters towards the poles and away from the tropics, while increased acidity is threatening habitats such as coral reefs and the future of shellfish like oysters, clams and mussels, says Oceana in its new report, Ocean-Based Food Security Threatened in a High CO₂ World.

Even a 2°C rise in temperature is too much for existing coral reefs to bear, according to the data published in Nature.

Based on current projections by Climate Action Tracker, the atmosphere is likely to heat up an average of 3-4°C before then.

"Despite the inclusion of optimistic scenarios concerning rates of evolutionary adaptation, our results confirm that coral reef ecosystems face considerable challenges under even an ambitious mitigation scenario that constrains global warming to 1.5°C above pre-industrial temperatures," say the researchers.

"Our projections suggest that most coral reefs will experience extensive degradation over the next few decades given the present behaviour of corals to thermal stress. To protect at least 50% of the coral reef cells, global mean temperature change would have to be limited to 1.2°C (1.1–1.4°C), especially given the lack of evidence that corals can evolve significantly on decadal timescales and under continually escalating thermal stress. There is little doubt from our analysis that coral reefs will no longer be prominent within coastal ecosystems if global average temperatures exceed 2°C above the pre-industrial period," write the researchers. 

Coral is actually fairly adaptive over time, say the scientists who authored the report. It can survive prolonged heat, but higher acid levels in oceans around the world are reducing coral thermal tolerance. GHG emissions have thus far been mostly absorbed by the world’s oceans – which are now saturated – and are 30% more acidic than baseline levels.

The rise in greenhouse gases has led to much more dramatic temperature rise than scientific models anticipated, despite a commitment by the countries attending the 2010 United Nations climate meeting in Cancun, Mexico to limit global temperature increases below 2°C.

“It’s very important to get people motivated to do their fair share,” Malte Meinshausen, from the School of Earth Sciences at the University of Melbourne, and one of the report’s co-authors, told Inter Press Service. “A strong international agreement is essential if we’re to have any hope of getting emissions low enough.”

Aong with their calls for more pollution and climate regulation to address the world’s warming oceans, researchers are also accelerating reef conservation projects. 

For example, scientists are harvesting coral eggs and sperm from sites in Hawaii, Australia and the Caribbean with an eye toward restoring and rebuilding reefs damaged reefs. And scientists from Scotland are testing robotics technology in the form of coral bots to help repair damaged deepwater corals.

For more about the link between rising temperatures and coral degradation: