SPF 1000?

In 2020, the world’s largest reef, the Great Barrier Reef in Australia, experienced its third mass bleaching event in the last five years (Nelson, 2020). Exacerbated by climate change, extreme heat waves bleach coral as their thermal tolerance and photosynthetic symbionts are exceeded (Hoegh-Guldberg, 1999). While bleaching does not always lead to organism death, it reduces growth rates and increases the chance of mortality. As coral reefs are considered the rainforests of the ocean due to their immense biodiversity, it is crucial that we protect them (McIntyre, 2010). To do so, geoengineers are working on a temporary solution by brightening clouds to act as a ‘atmospheric sunscreen’.

Many researchers throughout the world are modelling the effects of brightening clouds on the temperature of the water below them. As brighter, whiter, clouds reflect more sunlight, they can prevent extreme heat waves from impacting the marine temperature (Figure 1) (Nelson, 2020). Instead of making new clouds, they work to brighten the existing clouds that lie low in the atmosphere above the reefs. Cloud brightness is determined by the number of droplets which form the cloud condensation nuclei (Latham et al., 2014). The number of droplets is determined by the number of particles (known as seeds) in the air, as every droplet in a cloud requires a tiny particle floating around it in order to condense. Thus, these machines spray seawater upwards as tiny droplets to allow for water evaporation. Then, the miniscule salt crystals leftover float into the air. By evaporating seawater into these salt crystals, additional cloud droplets are formed which enhance the cloud droplet concentration and thus its brightness and albedo (Latham et al., 2014).

Figure 1. An illustration of marine cloud brightening. The sprayer produces small droplets of water that evaporate to leave miniscule salt crystals that brighten clouds. With increased brightness, the albedo increases, and therefore more sunlight is reflected, preventing incoming heat from warming the ocean (News Direct, 2012).

While the process may be theoretically simple, the execution is logistically very difficult. Dr. Daniel Harrison, an oceanographer at the Southern Cross University in Australia, along with his team have become the first to test the methods out in the field (Figure 2) (Nelson, 2020). While their experiment was successful, it was only 1/10th of the scale necessary to make a real difference on cloud brightness. To make a large-scale difference, it is estimated that it would require 800 seawater spraying stations (Nelson, 2020). While they have tested them on ships, this contributes to emissions, which furthers the environmental impact of the project. Some proposed solutions include dedicated barges for the technology in the summer or placing the sprayers on existing boats that travel in the area.

Figure 2: A seawater sprayer onboard a ship in the Great Barrier Reef. The logistical challenge of brightening clouds includes the implementation of large scale spraying methods that do not further contribute to emissions (CBC, 2021).

Nevertheless, brighter clouds are a temporary solution. They require a lot of costly infrastructure, and therefore can only be implemented in the direst of circumstances. While this possible solution is celebrated by many, it is important to note that while cloud brightening may help delay coral bleaching, if emissions continue to rise it will not be able to keep the water cool enough forever. We must therefore tackle climate change itself by initiating collaboration between scientists, policymakers, and individuals to foster systemic changes in how we interact with the environment.


CBC, 2021. Cloud-based sunscreen could help protect the Great Barrier Reef from future heat damage | CBC Radio. [online] CBC. Available at: <https://www.cbc.ca/radio/quirks/oct-9-nobel-prize-winners-in-physics-and-chemistry-a-super-hot-planet-with-calcium-wind-and-more-1.6203540/cloud-based-sunscreen-could-help-protect-the-great-barrier-reef-from-future-heat-damage-1.6203554> [Accessed 26 Nov. 2021].

Hoegh-Guldberg, O., 1999. Climate change, coral bleaching and the future of the world’s coral reefs. Marine and Freshwater Research, 50(8), pp.839–866. https://doi.org/10.1071/mf99078.

Latham, J., Gadian, A., Fournier, J., Parkes, B., Wadhams, P. and Chen, J., 2014. Marine cloud brightening: regional applications. Philosophical Transactions: Mathematical, Physical and Engineering Sciences, 372(2031), pp.1–11.

McIntyre, A., 2010. Life in the World’s Oceans: Diversity, Distribution, and Abundance. John Wiley & Sons.

Nelson, J., 2020. Scientists trial world-first ‘cloud brightening’ technique to protect corals – Southern Cross University. [online] Available at: <https://www.scu.edu.au/engage/news/latest-news/2020/scientists-trial-world-first-cloud-brightening-technique-to-protect-corals.php> [Accessed 26 Nov. 2021].

Scientists push for combating global warming with cloud brightening. 2012. News Direct. Available at: <https://www.youtube.com/watch?v=cgJyw2cTrW4> [Accessed 26 Nov. 2021].

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