Author: Vani Tripathi

Have you ever wondered if climate change could push humanity towards its collapse?

The signs are already around us - from the relentless heatwaves and devastating floods to rising food prices caused by damage to crop yields and increased acidification to our oceans.

Recently, in response, one of the most widely talked-about proposals to reduce global warming is called Stratospheric Aerosol Injection (SAI). This is a solar geoengineering technique that involves spraying tiny reflective particles known as aerosols into the stratosphere (upper atmosphere) in order to reflect sunlight and ultimately cool the planet. This concept takes inspiration from the natural phenomenon, called “Volcanic Cooling”. When volcanoes erupt explosively, they emit vast amounts of Sulphur Dioxide (SO₂) in the stratosphere. The Sulphur Dioxide released forms sulphate aerosols that reflect sunlight. This is known to cool the Earth temporarily - as seen after the 1991 Mount Pinatubo eruption, which reduced global temperatures by about 0.5°C for over a year. 

Inspired by this effect, SAI aims to replicate this process in a more controlled manner. However, while it may cause temporary reduction in global temperatures, there are significant environmental trade-offs. This includes frequent acid rain and potential disruption to ocean currents like the AMOC or North Atlantic Oscillations (NAO). 

Another critical concern is ocean acidification, which continues unabated because SAI does not reduce atmospheric carbon dioxide levels.

As oceans absorb over one-third of all human induced CO_2,, their pH drops which allows for leaching as carbonic acid is formed. In this process, as carbonic acid is a weak acid, hydrogen ions are dissociated which hinders calcification by restricting the growth of shells and protective layers of aquatic organisms. Ultimately, elevated carbon dioxide levels through burning fossil fuels or air pollution threaten coral reefs through bleaching and put marine ecosystems - vital for biodiversity and human food sources at serious risk!

These environmental threats, albeit different in origin, could collide in unexpected ways under certain geoengineering strategies like SAI.

One major concern posed by SAI is the potential to disrupt thermohaline circulation.

A core aspect of thermohaline circulation is to drive “The Global Conveyor Belt”. This circulation is driven by differences in the density of seawater, which are controlled by temperature (thermo) and salinity (haline). In the North Atlantic, colder, saltier water is denser and sinks deep into the ocean creating a downward flow that pulls in warmer surface water from other regions like the Tropics. This continuous movement helps distribute heat across the planet, stabilising weather patterns and preventing many parts of the world from experiencing extreme or lethal climate conditions. Without this density-driven circulation, the global climate could become far more erratic and hostile. 

Although SAI is proposed as a method to counteract global warming, it may actually result in the weakening of the temperature gradient between the tropics and the poles, reducing the flow of warm surface water northward and slowing down this crucial system.

As stated by Claudia Wieners at the Utrecht University in Netherlands, “Greenhouse gas mitigation helps less than stratospheric aerosol injection”. This statement reflects the controversial argument that SAI may be more effective at quickly reducing global temperatures - but temporarily. If implemented after decades of insufficient climate action, when the tipping points are approaching or already crossed - SAI could end up doing more harm than good. For example, it may increase the frequency of acid rains due to sulphur dioxide emissions. In particular, it may entirely weaken or lead to the collapse of the AMOC, which plays a key role in regulating parts of the world’s temperatures like the Indian Ocean where the nutrient-rich upwelling supports marine ecosystems - now at risk due to the increased intensity of the heatwaves. This means that global warming is more perceptible to accelerate, expanding more arid lands and rising sea levels, potentially causing temperatures to overshoot the Paris Climate Agreement’s of limiting global temperature rise to below 2°C. 

In conclusion, while Stratospheric Aerosol Injection presents an intriguing short-term solution to reduce global temperatures, its potential environmental consequences cannot be overlooked. Disruptions to oceanic systems such as the thermohaline circulation, increased acid rain, and unabated ocean acidification pose significant risks to ecosystems and future generations of mankind. Without addressing the root cause - greenhouse gas emissions - SAI could inadvertently accelerate climate instability and undermine international climate goals including PCA. Hence, it is crucial to approach geoengineering with caution, prioritising comprehensive and sustainable climate mitigation strategies alongside any experimental technologies where the pros outweigh the cons.

Citations: Wieners, C. (2024, June 14). Burning fossils like hell and cooling in 2080 – what could possibly go wrong? - News Scientist (2025, 19th July) Why the geoengineering debate has never been more urgent

Carrington, D. (2025, May 7). Real-world geoengineering experiments revealed by a UK agency. The Guardian.

Shepherd, J., & Lenton, T. (2012). Ocean acidification in a geoengineering context. 

Royal Society. (2009). Geoengineering the climate: science, governance and uncertainty.