Tiny aerosols have a major influence on cloud formation

Recent research has revealed a fascinating detail about cloud formation that might significantly deepen our understanding of climate change. This collaborative study, which utilized global satellite data and direct observations off the California coast, shows that aerosol particles as small as 25-30 nanometers – considerably smaller than previously believed – are crucial for cloud development.

“Clouds in Earth’s atmosphere are of fundamental importance for the climate by regulating the reflection of sunlight into space and interacting with thermal radiation from Earth,” noted the study authors.

Focusing on the behavior of cloud condensation nuclei

Clouds, complex and pivotal components of Earth’s atmosphere, present the greatest challenge in accurately predicting climate changes. Their formation is influenced by large-scale weather systems that span hundreds of kilometers and by interactions at the molecular level.

“Clouds are an essential part of Earth’s climate system. At the same time, clouds constitute one of the largest uncertainties in our understanding of climate change,” noted the researchers.

The study, focusing on the behavior of cloud condensation nuclei within marine stratus clouds, reveals that the size threshold required for these nuclei to trigger cloud formation is much smaller than the established norm of 60 nanometers.

Cloud formation occurs under two primary conditions: the atmosphere must be supersaturated with water, and there must be a seed particle or nucleus around which water can condense.

Traditionally, it was believed that these nuclei had to be relatively large. However, researchers from The Technical University of Denmark, the University of Copenhagen, and the Hebrew University of Jerusalem have found that even smaller proto-seeds can serve as effective nuclei.

“Here, we show that the supersaturation in marine liquid clouds is significantly higher than in the conventional view. As a consequence, much smaller aerosols can serve as cloud condensation nuclei. This can make cloud formation more sensitive to changes in aerosol properties than previously thought,” wrote the researchers.

Surprising role of smaller aerosols in cloud formation

Henrik Svensmark, a senior researcher at DTU Space and lead author of the study, emphasized the sensitivity of cloud formation to these smaller aerosols, especially in regions dominated by marine stratus clouds.

“Since the proto seeds can be much smaller than previously thought, cloud formation is more sensitive to changes in aerosols than previously thought, especially in pristine areas,” said Svensmark.

This sensitivity arises because smaller aerosols can be activated into cloud droplets in conditions where water is highly supersaturated.

Essentially, the denser the water vapor, the smaller the necessary seed particle. This means that in areas with higher water supersaturation, even minuscule aerosol particles can catalyze cloud formation.

The research utilized measurements from marine stratus clouds gathered in 2014 by Nevada researchers, alongside global data from the MODIS satellite instrument.

These combined observations revealed a consistent pattern of higher-than-expected supersaturation across the globe, which in turn adjusts the scale of critical seed size downwards.

Future implications for climate modeling

“About half of all cloud condensation nuclei are formed by tens of thousands of molecules clumping together one by one, forming an aerosol particle. That takes time; the longer it takes, the larger the risk of getting lost,” explained Svensmark.

“Current models show that due to the growth time, most of the small aerosols are lost before they grow to the critical size, and thus, cloud formation is rather insensitive to changes in the production of small aerosols. Our results change this understanding as aerosols must grow much less, which is important for modeling clouds and climate predictions.”

In simple terms, the discovery that smaller aerosols can effectively contribute to cloud formation suggests that climate models need to be recalibrated to account for these dynamics. This could potentially improve our predictions of future climate scenarios and provide a clearer picture of how atmospheric changes are influencing our environment.

Furthermore, the study not only challenges established paradigms in climatology but also opens the door for further investigations into the delicate interplays at the heart of our planet’s climate system.

The study is published in the journal Geophysical Research Letters.

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