Coral reefs are in hot water – we may need geoengineering to cool things down

Coral reefs are among the great natural wonders of the earth, but they are in hot water. The IPCC projects that up to 99% of the world’s coral reefs will be lost with 2C of warming. Even if we meet the Paris Agreement’s most optimistic target of capping warming at 1.5C, we face the loss of 70-90% of the world’s coral reefs. The gradual rise in ocean temperatures will contribute to this loss. But the main driver is the increased frequency and intensity of marine heatwaves. Warm water temperatures cause coral to expel zooxanthellae, leading to coral bleaching.  Australia’s Great Barrier Reef – a national and international icon – has lost 50% of its coral cover in the past 3 years as a result of just two consecutive bleaching events.

With this recent experience and the prospect of worse to come, it is no surprise that scientists and reef managers are searching for ways to promote reef recovery following bleaching events, and protect the Great Barrier Reef from future marine heatwaves.

Some of the measures being trialled are aimed at boosting coral abundance and recruitment. These include forms of coral “farming” and stabilizing reef rubble to promote coral regeneration. However, more controversial proposals are being investigated to prevent further decline of the reef during extreme conditions, by manipulating ocean or atmospheric conditions to lower water temperatures over part of the reef. The Australian and Queensland Governments are funding research into the feasibility of three such proposals.

Two proposals involve ”shading” the reef to reduce warming of shallow waters from direct exposure to the sun. One proposal is the application of a biodegradable polymer film that can act like a ‘sunscreen’ for coral. The other involves increasing the brightness of clouds over the GBR so they reflect more solar energy back into space. This marine cloud brightening proposal might be thought of as a type of local (or regional) solar radiation management. This proposal involves spraying minute salt particles into low-lying marine clouds to increase their brightness. The third approach involves reducing the temperature of shallow waters near corals by mixing them with cooler waters pumped from 10-30 metres below. This technique is intended to overcome the “stratification” of the water column above and below corals on very hot days, which prevents the natural mixing of warmer shallow and cooler deeper water.

At present, these proposals are all fairly small-scale and would likely be aimed at protecting ecologically, or economically-high-value areas of the reef. The water mixing option, for example, is being considered for an area that has high tourist activity because of the presence of two large recreational pontoons. It’s also worth noting that none of the techniques would prevent coral bleaching where the marine heatwave is due to the arrival of a body of pre-warmed water, as the heat is not then coming from within the water column itself. But the prospect of losing one of Australia’s most economically, culturally and ecologically important natural assets justifies placing all response options on the table, even controversial proposals that involve solar radiation management.

In our paper, we argue that as small-scale research and testing of recognized forms of geoengineering, these proposals have implications well beyond management of the Great Barrier Reef. The polymer sunscreen might be considered a small-scale form of solar radiation management. Its significance lies in the fact that it proposes applying the film directly to the water surface. In contrast, the water mixing proposal is not aimed at increasing reflectivity or removing CO2 (the two key categories of geoengineering) but the proposal will likely use similar technology to that being considered for a form of CDR known as marine upwelling. Marine cloud brightening is well-recognised as a form of solar radiation management. If it were deployed at large enough scale, it has the potential to influence weather conditions over areas area beyond Australia’s maritime jurisdiction.

Australia has a strong governance regime for managing the Great Barrier Reef, but the way it applies to these geoengineering proposals is not consistent. Field testing of the polymer film took place this summer under a research permit issued by the national agency with responsibility for managing the Great Barrier Reef Marine Park. Water mixing may not be labeled as a research proposal, but instead as a form of adaptation management activity. It is not even clear that MCB would take place within the jurisdiction of the reef Authority.

To be clear, we are not opposed to these proposals. Rather, we think they need to be governed as part of a coherent policy that articulates the role for such interventions alongside Australia’s climate mitigation and adaptation agendas. Why do we need more robust governance of such small-scale and early-stage geoengineering research? Experience in the United Kingdom and elsewhere shows that there can be significant public backlash if activities are not subject to proper public consultation and engagement. Australia’s current laws do not guarantee robust governance for field testing or eventual deployment of these technologies. If we are to pursue this suite of climate interventions more actively, we should have clear processes of risk assessment and public engagement at the earliest stages in order to build legitimacy and trust.

The issue of geoengineering governance has been considered for some time at an international level, but recent events suggest that the international law system cannot be relied upon to develop necessary mechanisms anytime soon. In March 2019, efforts to pass a United Nations Environment Assembly resolution calling for a detailed report on solar radiation management and carbon dioxide removal-– a key first step toward developing more robust governance mechanisms – failed. For the time being, domestic legal systems will have to lead in developing robust governance mechanisms for geoengineering research and deployment. By highlighting the inadequacies of our current laws, these GBR proposals should serve as a wake-up-call for Australia to develop a coherent national policy on climate intervention technologies more generally.

Read the full paper in the journal Climate Policy.

Dr Kerryn Brent is Lecturer in Law and member of the Centre for Marine Socioecology at the University of Tasmania, and a Deputy Director of the Australian Forum for Climate Engineering

Jan McDonald is Professor of Environmental and Climate Law and member of the Centre for Marine Socioecology at the University of Tasmania, and a Deputy Director of the Australian Forum for Climate Engineering.

Dr Jeff McGee is a Senior Lecturer in Antarctic and Climate Law at the Faculty of Law and Institute for Marine and Antarctic Studies at the University of Tasmania. He is also Director of the Australian Forum for Climate Engineering.

2 thoughts on “Coral reefs are in hot water – we may need geoengineering to cool things down

  1. How is it that Australia and Queensland governments are so keen on testing marine geoengineering to mitigate ocean heat to prevent coral bleaching, while the devastating effects of humdrum pollutants & sediments from agricultural runoff & erosion and poor land & coastal zone management also continue to threaten the health of the GBR?

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