We often think of the fight against air pollution as an unequivocal good—and for human health, it certainly is. But what if the cleaner air we breathe is also warming our planet in unexpected ways?
Since 2011, northwestern Pacific has been warming at an alarming rate of about 0.76 °C per decade—seven times faster than the global average ocean warming. This isn't just a statistic; it fuels more intense and frequent marine heatwaves, disrupts ecosystems, and can trigger climate disasters over densely populated East Asian coasts. However, the mechanisms underlying this abrupt warming remain inadequately understood. In our recent study published in Communications Earth & Environment, we uncovered a compelling climate story from the northwestern Pacific Ocean: a period of rapid warming that began after 2011 appears to be largely a direct consequence of successful air pollution control policies in East Asia.
A Potential Warming Effect
When scientific discussions turn to global ocean warming, greenhouse gases like CO₂ have long dominated the conversation. Decades of research have firmly established their leading role in driving large-scale oceanic temperature increases. Yet this established narrative may be overlooking another crucial human factor. Our energy budget analysis revealed a surprising lead actor: a significant increase in solar radiation (shortwave radiation) reaching the ocean surface. This enhanced heating explains about 72% of the sea surface temperature rise in the region. So, what was letting in all that extra sunlight?
The answer lies in aerosols. These tiny particles, released from industrial activities and other human sources, have a cooling effect on the climate. By reflecting shortwave radiation and serving as cloud condensation nuclei, they have offset a portion of the warming caused by greenhouse gases. However, in recent decades, and especially post-2011, East Asia has implemented stringent clean air policies. These successful actions have led to a dramatic reduction in aerosol emissions. While this dramatically improved air quality and public health, it also began to thin this man-made "shade". We began to suspect that the removal of this planetary coolant was unmasking a powerful warming effect.
Aerosols act as cloud condensation nuclei for cloud fraction. Fewer aerosols mean fewer cloud droplet number concentration, which can lead to the reduction in overall cloud cover, especially the low cloud cover, which are very effective at reflecting sunlight. From 2011 to 2022, low cloud cover over the northwestern Pacific decreased significantly. With fewer clouds, more shortwave radiation could reach the ocean surface, contributing to this dramatic warming. The potential warming effect of aerosols prompts us to reexamine the rationale behind current air cleaning policies.
The Nonlinear Relationship Between Aerosols and Clouds
Intriguingly, we have found that the ocean didn't start warming immediately as emissions fell. We observed a five-year lag between the start of significant emission reductions and the accelerated warming. This delay is governed by a "threshold-triggered" nonlinear effect in aerosol-cloud interactions. Our analysis shows that cloud cover only begins to decrease significantly once aerosol concentrations drop below a critical tipping point (AOD ~0.2). Before that threshold is crossed, the system is relatively unresponsive. This finding helps explain the timing of the abrupt warming shift.
Validating the Findings with Climate Models
To analyze the different effects of climate forcing, we turned to multiple climate models from the CMIP6 project. We used single-forcing experiments to isolate the effect of individual factors like aerosols, greenhouse gases and natural forcing.
The results were striking: anthropogenic aerosol reduction was the dominant driver, accounting for about 66% of the observed warming trend in the northwestern Pacific from 2011-2020—a contribution that surpassed that of GHGs during this specific period. The models corroborated our proposed mechanism, showing that aerosol forcing led to increased surface solar radiation through decreased cloud cover.
Implications for a Warming Future
Our research reveals a critical trade-off: while reducing aerosol pollution is essential for cleaning our air, it unexpectedly becomes a potent driver of regional ocean warming. This abrupt warming, in turn, triggers a cascade of impacts—intensifying extreme weather events, disrupting fragile marine ecosystems, and accelerating biodiversity loss.
These findings underscore an urgent need for interdisciplinary solutions to address the compound risks posed by this aerosol-mediated climate whiplash, where the well-intentioned termination of a cooling forcing paradoxically introduces new environmental challenges. The path forward requires policies that simultaneously secure the benefits of clean air and mitigate the unintended warming through aggressive, coordinated reductions in greenhouse gas emissions.
We sincerely thank the editors of Communications Earth & Environment and the anonymous reviewers for their insightful comments and suggestions, which greatly improved the manuscript. We also extend our heartfelt gratitude to the funding agencies, and to the climate modeling groups and data centers for making their simulations and datasets publicly available. This work would not have been possible without this collective support.