Can we ‘turn down the sun’ to save our collapsing fisheries?

In this guest post, Francesca Young, a master's student at UCL, explores the potential and limits of Solar Radiation Management as a means of addressing the impacts of climate change on fisheries.

In 2017, 100 million Pacific cod suddenly disappeared from the waters off the coast of southern Alaska. This 70% reduction over 2 years represents an unprecedented crash of fishery worth $100 million annually. Researchers identified the prime suspect as “The Blob”, a 4 million square kilometre expanse of unusually warm ocean water, with temperatures 2.5°C above the norm. This change, although seemingly small, was a catastrophic upheaval for marine ecosystems.  

As our planet comes close to breaching the 1.5°C threshold which scientists have warned would be catastrophic for our environment, marine heatwaves, such as “the Blob”, are becoming increasingly common. Our oceans, absorbing 93% of excess heat from greenhouse gas emissions, have seen the highest temperatures on record in the last decade, with the greatest impact felt in the ocean’s surface layers, home to most marine life. 

Figure 1. Marine heat-waves triggering extensive fish die-offs, resulting in severe consequences for local fisheries. Source: The Conversation

Ecosystems in crises 

The effects of “the Blob” began at the base of the marine food web with phytoplankton, the microscopic plants which all life relies on. In Alaska, phytoplankton populations dwindled due to warmer temperatures changing circulation patterns and altering nutrient flow. As the foundations of the food chain starved and weakened, the effects propagated upwards, causing population crashes of larger marine creatures from fish like the Pacific cod to whales. 

Marine heatwaves are not only impacting species directly but are also driving fish migration poleward toward cooler waters, estimated at 18-32 miles per decade. Additionally, rising temperatures are creating dead zones — areas with insufficient oxygen for marine life to survive. These changes are detrimental as it disrupts commercial fisheries which contribute $230 billion to the global economy, crucial for food security. Less developed countries and indigenous communities are the most vulnerable, as they are heavily reliant on fisheries and have limited capacity to adapt. 

Since the early 1980s, the number of days with marine heatwaves have doubled. Fisheries worldwide have reported a 4.1% decline, with some regions seeing 90% reductions in marine food sources. The future is worse; even in the most optimistic emissions scenarios, projections unanimously forecast global declines in marine biomass, with proliferations of ‘blobs’ across the globe. Without intervention, these heatwaves will grow in both duration and intensity, pushing marine organisms to collapse, along with the fisheries and economies that depend on them. 

A controversial path to cooling the planet 

As an emergency resort, scientists have proposed climate manipulation strategies like solar radiation management (SRM), which aims to reflect sunlight and rapidly cool the planet at relatively low cost. One SRM method called stratospheric aerosol injection (SAI), involves injecting a layer of reflective particles, such as sulphate, into the stratosphere to reduce the amount of solar radiation reaching the surface. Model simulations show that when you turn on SAI, global temperatures are successfully stabilised at safe target values (1.5°C) and increases in marine heatwaves are prevented, potentially halting fishery biomass declines. 

However, not all models agree, and this seemingly straightforward solution has significant risks. Some SAI models have demonstrated altered precipitation and ocean circulation patterns that could disrupt phytoplankton growth, leading to an overall decrease in ocean productivity. Moreover, SRM’s impacts exhibit great variation, potentially benefiting some regions with productive fisheries while adversely impacting others This patchwork effect raises serious concerns about localised food security and exacerbating climate inequalities. 

Figure 2. Stratospheric aerosol injection involves the injection of reflective sulphate aerosols via high-altitude planes into the upper atmosphere, reflecting a small amount of sunlight from the Earth’s surface and helping to cool the planet. Source: Knowable magazine

Beyond temperature control: SRM’s ‘blind spot’ 

One thing that is certain however, is that SRM fails to address a key contributor to marine ecosystem collapse: ocean acidification. Ocean acidification occurs when the ocean absorbs atmospheric CO2, decreasing seawater pH, adversely affecting marine life, especially coral reefs. Coral reefs are important as they recycle nutrients needed for phytoplankton, contributing to global ocean productivity, as well as feeding fish that support commercial and subsistence fisheries, estimated to provide a value of $100million to US fisheries. Even if SRM successfully lowers global temperatures, the continued accumulation of CO2 would still lead to a more acidic ocean, causing up to 90% coral reef loss by 2045, threatening marine ecosystems and the economies that rely on them.  

Moreover, a sudden ocean cooling may induce ocean circulation changes which could even accelerate deep ocean acidification and broaden the affected areas, potentially acidifying almost the entire ocean. Dr Kelsey Roberts, an expert in marine conservation, stated that “if you lower the temperature globally, but you don’t do anything about the existing CO2 in the atmosphere, you could end up with a cooler but more acidic ocean, which will create a whole new set of problems”.  

Roberts emphasises that SAI should only be considered if coupled with industrial-scale Carbon Dioxide Removal (CDR) strategies, which suck and capture CO2 from the atmosphere. This combination is crucial for tackling both the symptoms (rising temperatures) and the root cause (CO2 emissions) of climate change. Without addressing the latter, SAI alone could prove to be far more detrimental than traditional emissions reductions. 

Fisheries at a crossroads: The uncertain future of SRM 

Marine ecosystems are delicate and complex and the research into ecological consequences of SRM have barely begun to be investigated. Critically, before any decision can be made about SRM deployment, further research must be done to determine the variety and magnitude of ecosystem impacts that it would cause. Whilst it offers quick fixes to ocean surface temperatures, can we ethically justify a solution that might benefit some regions while severely harming others?  

Whilst the need for action is indisputable, SAI’s failure in improving ocean acidification, its unequal global impacts, potential unforeseen consequences, and political and ethical complications all cast doubt on the suitability of SAI as a viable climate solution. Our best course of action may be to commit to significant emissions reductions and focus on adapting to the inevitable consequences of our alterations to the planet, as further manipulating our environment could potentially lead to more harm than good.  

FIN

Notes and Acknowledgements

As part of my new course at UCL, “The science, policy and ethics of climate intervention”, my students researched and wrote an accessible article in the style of The Conversation. Francesca’s was one of the best, but The Conversation only accepts submissions from Academics and PhD students, and so I’ve published it here.

As part of her research, Francesca interviewed Kelsey Roberts who also helped review Francesca’s work for accuracy.

I’d like to thank Will De Freitas and Daisy Dunne for their guest lectures that helped the students learn how to write on scientific topics for a general audience.