Human Impacts: Manmade Aerosols Cause Clouds to be Taller and Larger

Human activity can actually affect clouds and even create them. Understanding exactly how these clouds affect the climate, though, is difficult to piece together. Yet now, scientists have taken a closer look at cloud formation and have found exactly how much human activities have impacted it.

Clouds form when tiny particles, called aerosols, rise in the atmosphere. These aerosols, which can include natural materials such as sea salt or manmade ones like soot, form nuclei around which cloud droplets condense. In a relatively clean environment, clouds can only grow as large as the amount of aerosols in the atmosphere allows.

What scientists wanted to know if is the current load of aerosols exceeds a certain limit in cloud formation. The scientists created a model of cloud formation and found that an increase in aerosols would result in taller, larger clouds. Yet actually testing this model was a bit more difficult.

The scientists decided to test their model near the horse latitudes, subtropical regions far out in the oceans. There are relatively low levels of aerosols in this region so if the model was correct, transitions from one type of cloud formation to another would be dramatic. The scientists compared daily satellite images of cloud cover over this region and measurements of the aerosol load to the predictions of the model. They eventually found that their model closely resembled satellite observations.

"We showed that convective clouds do not necessarily stop being aerosol-limited; under relatively polluted conditions the increase in aerosol loading will make the clouds taller, larger and their rain-rate stronger," said Ilan Koren, one of the researchers, in a news release. "As the area of this cloud cover grows, it reflects more of the shortwave radiation; but as the clouds get taller, their greenhouse effect becomes more significant, counteracting about half of their total cooling effect."

The findings reveal a little bit more about cloud formation and show how human activity can drastically impact cloud cover, which could impact climate.

The findings are published in the journal Science.