By Mengfan Li, Kevin Peng, Rohan Rajan, Harshvardhan Sanghi and Megan Wang

Though there has been some push to reduce carbon emissions in recent years, these efforts pale in comparison to the magnitude of impact required to prevent the worst effects of climate change. Even if we were to halt all our emissions today, the concentration of CO₂ already present in the atmosphere is enough to cause warming for the next several decades. However, ecosystems already buckling under the strain of our current temperatures need immediate treatments.

In short, we must flatten the curve of climate change.

There are few who are more desperate for time than the scientists searching for ways to save the Great Barrier Reef. Mass bleaching has already killed half of the coral reef and the rest is almost certain to die soon without intervention. Most of the damage has been inflicted by significant spikes in surface sea temperatures, which stress the coral and make them more susceptible to disease and death. Worryingly, the Intergovernmental Panel on Climate Change predicts that even if we limit warming to 1.5℃, we face the loss of up to 90% of the reefs.

However, an engineering technique called marine cloud brightening (MCB) provides a glimmer of hope by allowing us to flatten the peaks of extreme temperatures. First proposed by American climatologist John Latham, seawater is sprayed into the atmosphere, allowing water vapor to condense upon the salt particles and formulate clouds with higher albedo. These clouds have greater ability to reflect incoming solar radiation, which can then cool surface temperatures. This can be used to cool oceans during the extreme weather events that decimate coral reefs.

MCB is uniquely positioned as a viable option to address extreme temperature events that drive global environmental destruction. Firstly, MCB is touted as a localized method that does not conflict with international frameworks. Other technologies, particularly the injection of sulfate aerosols into the stratosphere, alter the climate at such a global scale that international cooperation is necessary in order to implement them. Unfortunately, finding common ground can be potentially difficult, as different states may desire different average temperatures—what could benefit one state could potentially harm another. MCB’s localized effects overcome this by allowing each country to make independent decisions.

Secondly, the impacts of MCB are estimated to last only for a matter of days or weeks, allowing for greater control and flexibility in its implementation. MCB can be used in short durations to control extreme temperature events and does not have to be used year-round, avoiding long-term changes in weather cycles and atmospheric composition. Alternate methods, like sulfate aerosol injections, may have a long-lasting impact on the ozone layer and rain cycles that are hard to remedy.

Public criticism directed at MCB often involves concerns about the negative effects of aerosols in the atmosphere similar to the environmental consequences of ship tracks, from which MCB was conceptualized. Research suggests that because the plumes emitted from these ships are brighter than the marine stratocumulus clouds that already exist within those regions, ship tracks may have contributed to atmospheric cooling in certain regions. Notably, the accidental brightening caused by ships had several negative consequences: the sulfur in the fuel was found to cause ozone depletion, acid rain and respiratory problems. Because MCB uses saltwater instead of sulfur, MCB essentially eliminates these drawbacks.

However, these arguments are not to say marine cloud brightening is without its uncertainties— in fact, there are many things we do not yet know about this method. For one, whether MCB should be implemented over the tropics or over Antarctic ice sheets is still in contention. There is also uncertainty regarding the magnitude of cooling it can achieve. Even though there are clear advantages to using MCB in conjunction with climate change mitigation efforts, we still need to address these uncertainties to affirm that MCB is effective. With rapidly deteriorating ecosystems like the Great Barrier Reef, we will need to address these uncertainties as soon as possible through additional research.

Researchers are working tirelessly to give the reefs a fighting chance against a constant onslaught of threats by engineering several technologies; of these, MCB stands out as one of the most promising. Reefs are invaluable to humanity not just for the economic value they generate. They are also critical links in the ocean’s food chain, protective buffers against storms and waves and an abundant source of new medicines. It would not be an exaggeration to say that to secure the future of coral reefs is to make a critical investment in our own survival.

Research, however, can be hastened only so much through cash investment—conducting field tests will require robust systems of local governance that currently do not exist. The governments of the world must create a framework for the governance of MCB’s testing and deployment as soon as possible, or we risk starting when it is already too late.

The authors are members of the Bass Connections project team DECIPHER: Decisions on the Risks and Benefits of Geoengineering the Climate. Mengfan Li (M.S. in Civil Engineering) and Harshvardhan Sanghi (B.S.E. in Mechanical Engineering) graduated this spring; Rohan Rajan will graduate this summer; Kevin Peng and Megan Wang are rising juniors.

Learn More

• Check out this team’s submission for the Fortin Foundation Bass Connections Virtual Showcase and browse the team’s website to learn more about their research.
• Read about this team’s plans for 2020-2021.
• Explore project teams and courses in the Energy & Environment theme.