Geoengineering Might Be The Last Chance For Coral Reefs

We are all aware of many of the myriad effects of climate change – higher temperatures, rising sea levels, more extreme weather events, but coral bleaching has tended to escape notice despite being one of the most acute problems facing our oceans right now. New research resulting from a worldwide collaboration suggests that we have reached a tipping point and a geoengineering technique called Solar Radiation Management may be the only way to save coral reefs from mass bleaching.

Bleached coral: the coral in the foreground has been bleached while that in the background is still healthy.Bleached coral: the coral in the foreground has been bleached while that in the background is still healthy.

Coral reefs are particularly vulnerable to climate change as they are susceptible to both rising ocean temperatures and increasing ocean acidification. Coral is made up of a symbiotic relationship between a structural component, the polyp, and photosynthetic single-celled organisms called zooxanthellae which provide the coral with its coloration. In exchange for using the polyps as a habitat, the zooxanthellae produce supplementary food for the coral. In times of stress, the zooxanthellae are expelled leaving just the white polyps behind and giving rise to the term coral “bleaching”.

The effects of bleaching are untenable for the coral; without their symbiotic partner, they begin to starve, growth and reproduction slow, they become increasingly susceptible to disease, and they eventually die. Imagine a not-at-all-distant future where the Great Barrier Reef is no longer a diver’s paradise brimming with life, but rather a dead expanse of calcium carbonate remnants; like an underwater boneyard. It’s not just divers who should be concerned however, a huge variety of sea creatures rely on the reefs and surrounding area for food and shelter. The chain reaction stemming from the death of the reefs will likely have far-reaching biological and economic impacts.


Healthy coral: this colorful specimen at the Great Barrier Reef teems with life. Image by Toby Hudson.Healthy coral: this colorful specimen at the Great Barrier Reef teems with life. Image by Toby Hudson.

The bad news is that it appears the increase in atmospheric CO2 and accompanying temperature rises have already passed the point where a reduction in emissions could stem the tide of coral bleaching. Scientists say that “even under the most ambitious future CO2 reduction scenarios, widespread and severe coral bleaching and degradation will occur by the middle of this century”. The good news is that there is an alternative, controversial though it may be.

Geoengineering, or climate engineering, is the term used to describe a large-scale, intentional interference with the Earth’s climate. While some endorse it as a viable means of combatting climate change, many others are worried about the potential unforeseen consequences of such a massive intervention. Solar Radiation Management (SRM) is one example of geoengineering solution in which aerosol particles are delivered to the stratosphere in order to reflect more incoming solar radiation, thus cooling the planet.

The researchers engaged in this study suggest that SRM may be the best chance for saving the planet’s coral reefs. As evidence, they employed computer models to project the extent of coral bleaching under various scenarios. To further back up their conclusions, they point to previous examples of naturally occurring SRM such as volcanic eruptions. These too result in excess particulates in the atmosphere and have been shown to contribute to reduced coral bleaching.

Erupting volcano: aerosol particles injected into the atmosphere by erupting volcanos have been shown to reduce global warming and coral bleaching. Image by Taro Taylor.Erupting volcano: aerosol particles injected into the atmosphere by erupting volcanos have been shown to reduce global warming and coral bleaching. Image by Taro Taylor.

Unfortunately, SRM can only help reduce the ocean temperature and will not impact the ocean acidification resulting from human CO2 emissions meaning our corals are still at risk. This study reveals the importance of considering and utilizing a wide variety of options when attempting to mitigate the effects of climate change. And we absolutely must if we want our children and grandchildren to still be able to enjoy the wonders of the Great Barrier Reef.

Via Nature Climate Change, Exeter University and Science Daily.