The Unintended Consequences of Geoengineering: A Focus on ENSO Disruption
Recent research from UC Santa Barbara has illuminated potential, and significant, risks associated with geoengineering strategies designed to combat climate change. While aiming to cool the planet, interventions like marine cloud brightening (MCB) and stratospheric aerosol injection (SAI) could trigger unforeseen consequences, particularly concerning crucial climate patterns like the El Niño-Southern Oscillation (ENSO).
The study modeled the effects of both MCB and SAI, revealing a stark contrast in their potential impacts. Surprisingly, SAI – dispersing aerosols high in the stratosphere to reflect sunlight – showed virtually no effect on ENSO. However, MCB, which involves spraying seawater into low-lying marine clouds to make them more reflective, demonstrated a dramatic and concerning outcome.
Deploying MCB in the subtropical eastern pacific Ocean resulted in a projected 61% reduction in ENSO’s amplitude. Researchers were taken aback by the magnitude of this effect, noting that such a rapid and ample change is unprecedented, even under projected climate change scenarios.
The mechanism behind this disruption lies in a cascade of effects. MCB creates clouds with smaller water droplets, increasing reflectivity and cooling the surface. This cooling, though, reduces evaporation and atmospheric convection, leading to drier conditions. As this cooler, drier air moves westward across the Pacific, it strengthens equatorial winds, further suppressing rainfall and lowering sea surface temperatures. This ultimately destabilizes the conditions that drive ENSO, effectively “crashing” the cycle.
Researchers caution against implementing MCB in this specific region of the eastern Pacific due to the potential for these “super strong chain reactions.” While the study doesn’t condemn all MCB strategies, it emphasizes the importance of location. MCB deployed elsewhere might achieve global cooling, but would likely require a larger-scale intervention to yield comparable results.
Beyond ENSO disruption, the study also highlights broader ecological concerns. Blocking sunlight through geoengineering could reduce photosynthetic activity, impacting crop yields, forest health, and, critically, marine algae. These algae are foundational to the ocean food web and responsible for approximately 70% of atmospheric oxygen production. The research team is now investigating the potential impacts of these geoengineering proposals on marine ecosystems.
The findings underscore a critical point: geoengineering solutions are not neutral. even interventions aiming for the same global warming target can have drastically different regional climate impacts. As Associate Professor Samantha stevenson emphasizes, the crucial question is whether all potential consequences are being thoroughly considered before implementing such large-scale interventions. The study serves as a powerful reminder that addressing climate change requires a nuanced understanding of complex Earth systems and a careful evaluation of the tradeoffs inherent in any proposed solution.
