Marine Cloud Brightening: A Technique to Combat the Effects of Climate Change

Isabel Cline, Grace Gould, Wilson Hago

Introduction

Over the past decade, there has been a push to take action towards the climate crisis. As the effects of climate change have become increasingly more severe, there has been a widespread impact on communities, individuals, and entire ecosystems. There is not enough

time left to focus only on reducing our carbon emissions- there must be rapid action taken to stabilize rising global temperatures to prevent catastrophic disasters. Scientists are looking to take possible emergency measures, some of which consist of geoengineering techniques. More specifically, these comprise solar radiation management geoengineering techniques. One of these techniques is marine cloud brightening. The aim of marine cloud brightening is to produce a global cooling effect that could offset carbon emissions.

How it works

Marine cloud brightening sprays small submicron particles at or near the ocean’s surface. This is known as cloud seeding. By seeding the clouds with saltwater particles, the number of condensation nuclei increases. As a result, the clouds become brighter and more reflective. This is known as the albedo effect. Albedo is a measurement of the ability to reflect solar radiation. The whiter something is, the more solar radiation it reflects. By increasing the reflectivity of clouds, it increases the amount of solar radiation reflected back into space. The more solar radiation reflected back into space, the cooler the earth remains. Essentially, the goal of marine cloud brightening is to produce a cooling effect and mitigate rising global temperatures.

Factors that could influence effectiveness

A factor that influences the effectiveness of marine cloud brightening is the humidity. The formation for cloud droplets requires relatively high humidity, and the humidity near the ocean’s surface will be relatively 100%. The temperature will also influence the effectiveness of this technique. If the temperature is too cold, the spray heads could become frozen and not function properly. Lastly, the wind will also affect how successfully the saltwater particles are dispersed in air. If there is not enough wind then the salt water particles could be poorly mixed.

Particle Size

The particle size is essential in marine cloud brightening. If the particle size is too large or too small it will not increase the cloud’s reflectivity. Marine cloud brightening is exploiting the Twomey effect. The Twomey effect describes how the increased number of condensation nuclei may increase the amount of solar radiation reflected by clouds. In order to increase the number of condensation nuclei, it is better to have a greater number of small droplets than a smaller number of large droplets. The ideal particle size has been heavily debated, however, the proposed particle size for experimentation is around 0.8 microns.

The Nozzle

The nozzle would produce the spray generation of the saltwater particles above or near the ocean’s surface. Due to the small particle size, the nozzle would be inkjet printed for experimentation. For experimentation, the nozzle must be able to operate properly after an extended period of time. The seeding of the clouds could not operate on a frequent basis, therefore, it is important for the nozzle to be able to work after not being in use for weeks or months. For the nozzle to operate properly, there must be no solid content built up. Filtration prior to injection into the nozzle will likely be required. The nozzle can be flushed with fresh water every couple of minutes and then air dried with clean air to prevent the build up of salt in the nozzle.

The Wafer

The proposed saltwater particle distribution process is made up of a wafer which is a thin slice of a semiconductor. The microfabrication would allow very small features to be layered on top of each other. The microfabrication would allow very small features to be layered on top of each other. The use of silicon for insulator material reduces variability of the process and simplifies the fabrication process. The top layer is made out of crystal silicon. Crystal silicon is a popular material because it is strong; however, it can be very sensitive. The middle layer consists of silicon dioxide. The bottom layer of the wafer is made out of bulk silicon. The nozzle would be etched into this material.

Filtration

There would need to be filtration to prevent the clogging of the nozzle. Stephen Salter, a professor at the University of Edinburgh, with associates Thomas Stevenson and Andreas Tsiamis proposed a filtration method. The filtration process is composed of a set of eight filters. Seven of the filters would go to backflush the eight filters. The backflush would be changed every few minutes. Each filter would consist of two valves. One of the valves directs saltwater to the spray head and the other valve to the other filters. In order to prevent build up, the valves must not produce any debris. To combat this, it was proposed to use blister valves.

The vessel

According to a design by Stephen Salter, a vessel could be made of wind-operated flettner rotors. A flettner rotor is a smooth cylinder with disc end plates which is spun along its long axis and, as air passes at right angles across it, the Magnus effect causes an aerodynamic force to be generated in the direction perpendicular to both the long axis and the direction of airflow. Using flettner rotors allows for greater mobility. They have high agility and are able to rotate 180 degrees in any direction and stop efficiently. The spray heads will be placed vertically along the mast. This placement allows for a direct flow path for spray generation. The nozzles will be able to rotate downwind to maximize seeding. This placement also allows for spare spray heads or spray heads with different droplet sizes. For power generation, the use of four variable-pitch hydrofoils on hinged arms would generate enough energy. By using hydrofoils, it will decrease the amount of drag opposed to using conventional hulls. This method for power generation was also proposed by Stephen Salter.

Benefits

One of the benefits of marine cloud brightening is that it is a quick and effective solution that could prevent rising global temperatures. Once marine cloud brightening is implemented, the results are rapidly felt. The impacts of marine cloud brightening only last for a short period of time, which also allows for the process to also be quickly reversible. Another advantage is that this technique uses the natural substances of saltwater and wind instead of introducing human made substances into the environment. In addition, marine cloud brightening can be localized in its effects to target a specific area. This could include implementing it in the Arctic to prevent further melting or in the Great Barrier Reef to prevent further coral bleaching.

Policy on geoengineering

Currently, it is difficult to get government funding for marine cloud brightening. Thus, we must continue to spread awareness about marine cloud brightening to bring more attention to this technique to help the environment. In addition, the current restrictions and regulation in the ideal places for testing marine cloud brightening makes it difficult for experimentation. There is currently research being done at the University of Southern Cross to implement marine cloud brightening over the coral reef. However, there are many steps to go through to get approved for testing as the Great Barrier Reef is disappearing. Other work on marine cloud brightening is also being done at the University of Washington.

Public opinion on marine cloud brightening

The public opinion of geoengineering has faced some backlash. Studies have been conducted surveying the public on their thoughts regarding marine cloud brightening over the Great Barrier Reef. These surveys resulted in skepticism. The coral reef is a great treasure and many people want to preserve it and prevent further damage. There has not been much testing on marine cloud brightening as of now. Therefore, it is not a commonly known technique to battle the climate crisis. However, the public’s perception could be changed if there was more testing done to show the positive results.

Ethics of marine cloud brightening

Marine cloud brightening raises many ethical issues regarding implementation. This method along with the other geoengineering methods proposed to manage global temperatures has been perceived negatively. Scholars have explored the questions regarding manipulating the climate and the effects on humanity. One point raised is that manipulating the climate is similar to “playing God.” The questions regarding who gets to control the ‘global thermostat’ also arise. If this method were to be implemented all around the world this could lead to disagreements on who has control over the technology. In addition, scientists and scholars worry since this is a fast acting and effective way to manage global temperatures, humanity’s mindset on emissions would not change. They might think because this solution is working to offset climate change then they can keep emitting pollutants at our current rate.

Conclusion and Recommendation for Policy Makers

As the climate crisis continues to persist, there must be action taken to stabilize rising global temperatures. Marine cloud brightening could be one of the solutions to achieve this. There are numerous benefits to marine cloud brightening. It is fast-acting, reversible, and able to be localized in its effects. In addition, there are few risks associated with this technique. However, there is limited field testing done on marine cloud brightening. Marine cloud brightening uses all natural substances and should be encouraged by policy makers to be tested in local regions. A greater number of field tests is an important step in moving forward with this technology. This technique is precisely what we need to implement in order to help offset climate change and prevent catastrophic disasters.

References

S. Salter, T. Stevenson, and A. Tsiamis, Engineering Ideas for Brighter Clouds, 2014, 131–159

S. Salter, Initial Research for Marine Cloud Brightening, 2020

National Academies of Sciences, Engineering, and Medicine 2021. Reflecting Sunlight: Recommendations for Solar Geoengineering Research and Research Governance. Washington, DC: The National Academies Press. https://doi.org/10.17226/25762.