Reduced air pollution is making clouds reflect less sunlight

Reduced air pollution is a move towards the pre-industrial atmosphere, when it was noticeably *cooler* than it is now. Little Ice Age cool, in fact. The authors mention a paradox, but that’s not it. They say air pollution is or was ‘masking’ human-caused warming. Standard alarmist fare with a slight twist. The recent Nikolov and Zeller paper (here) has told a different story.
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Winter is setting in across the Northern Hemisphere, and with it, cold and cloudy winter days. Clouds play a vital role in the environment, providing rain but also reflecting sunlight before it reaches Earth’s surface, says The Conversation (via Phys.org).

But between 2003 and 2022, clouds over the North Atlantic and Northeast Pacific became less reflective, allowing more sunlight to reach the ocean surface and causing sea surface temperatures to rise.

My colleagues and I recently conducted research that shows global efforts to improve air quality have unintentionally accelerated climate warming by modifying clouds.

While cleaner air has major health benefits, decreasing the amount of particulate pollution has also reduced the cooling effect of clouds, accelerating climate warming.

Dimming clouds and rising temperatures
Our study relied on two decades of satellite data to analyze the impacts of changes in particulate pollution and climate warming on the clouds. The data shows that low-level clouds in the Northern Hemisphere have dimmed rapidly since 2003.
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A cleaner atmosphere, a warmer planet
Ultimately, our study exposes a paradox: cleaner air benefits human health while also revealing the full force of greenhouse-gas warming, which has historically been “masked” by the cooling effect of particulate pollution.
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In our study, we separated the effects of particulate air-pollution cuts from cloud changes driven by general warming. The results showed that declining aerosols accounted for 69% of the cloud reflectivity loss, while warming explained 31%.

Our simulations indicate that changes in cloud lifetime in response to having larger droplets (the Albrecht effect) proved more influential in the change in cloud droplet size itself (the Twomey effect).

Reduced cloud brightness in these ocean regions added about 0.15 watts per square meter (W/m²) per decade to Earth’s global energy imbalance, even though the regions cover only 14% of the planet’s surface. Rising global CO₂ levels added roughly 0.31 W/m² per decade during the same time, meaning cleaner air produced nearly half as much additional warming as CO₂ itself in those areas. [Talkshop comment – making evidence-free CO₂ assertions as usual].

This finding creates a policy challenge: air-quality improvements that save lives also remove a cooling shield that has been masking a significant portion of greenhouse-gas warming. Because aerosol emissions are projected to keep falling through mid-century, this “unmasking” could continue to contribute to faster rates of warming for decades.
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Importance of continued observation
The satellites observing clouds and aerosols are nearing the end of their mission, with a phaseout expected in 2026. Long-term satellite monitoring proved essential for revealing the link between cleaner air, dimmer clouds and regional warming, and will continue to be essential for understanding future warming.

Our results suggest that many climate models may underestimate near-term regional warming as air particulate pollution declines. Improving the representation in models of how aerosols affect clouds and continuing global observations will be critical for more accurate projections.

Full article here.