NASA Finds Polluted Clouds Hold Less Moisture & Cool Earth Less

Dec 23, 2004

A NASA study found some clouds that form on tiny haze particles are not cooling the Earth as much as previously thought. These findings have implications for the ability to predict changes in climate.
Andrew Ackerman, a scientist at NASA's Ames Research Center, Moffett Field, Calif., and his colleagues found, when the air over clouds is dry, polluted clouds hold less water and reflect less solar energy. Ackerman is the study's principal author.

Contrary to expectations, scientists observed polluted, low-lying clouds do not generally hold more water than cleaner clouds. Low clouds cool the planet by reflecting sunlight away from the Earth's surface, and more water makes a cloud more reflective.

Previously, scientific consensus was, since polluted clouds precipitate less, they should contain more water and reflect more sunlight back into space. Most predictions of global climate change assume less precipitation will result in clouds holding more water, reflecting more sunlight and counteracting greenhouse warming.

"The natural laboratory we used to look at the contrasts between clean and polluted clouds is a phenomenon called ship tracks, which are long lines of clouds with smaller cloud droplets that form on the exhaust particles from ships," Ackerman said.

"The results of this work should provide for more realistic treatment of polluted clouds in climate models, improving predictions of future climate," Ackerman said. "In the meantime, it's critical that we thoroughly test these new theoretical results. NASA's latest generation of Earth-observing satellites provides a powerful tool for doing just that, by observing how ship tracks are affected by the humidity of the air above them," he said.

Ship track measurements were taken off the west coast of the United States from polar-orbiting satellites and aircraft flying through the clouds. The Moderate Resolution Imaging Spectroradiometer (MODIS) Airborne Simulator instrument (comparable to the MODIS instruments on NASA's Terra and Aqua satellites), aboard a NASA ER-2 aircraft flying above the clouds, was also used to gather data. The measurements show cloud water decreases more often than it increases in polluted clouds.

To understand how cloud water changes in polluted clouds, the team of scientists created a 3-D computer model to simulate atmospheric motions and the formation of precipitation by clouds. They tested their model by comparing its predictions with measurements from field projects devoted to characterizing marine stratocumulus clouds.

After verifying the model reproduced the behavior of real clouds, the scientists asked their computer model how pollution affects clouds. In agreement with previous work, their computer simulations showed, when air over a cloud is humid, cloud water increases in polluted clouds. However, when air over a stratocumulus cloud deck is dry, surprisingly, water decreased in polluted clouds, consistent with the behavior observed in ship tracks.

Ackerman's co-investigators included Michael Kirkpatrick, University of Tasmania, Hobart, Australia; David Stevens, Lawrence Livermore National Laboratory, Livermore, Calif.; and O. Brian Toon, University of Colorado, Boulder. The researchers' findings appear in today's issue of the journal Nature.

Source: NASA

Explore further: Lockheed Martin successfully mates NOAA GOES-R satellite modules

add to favorites email to friend print save as pdf

Related Stories

Cool roofs in China can save energy and reduce emissions

Aug 28, 2014

(Phys.org) —Working with Chinese researchers, the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) has conducted the first comprehensive study of cool roofs in China and concluded ...

Pyrocumulonibus cloud rises up from Canadian wildfires

Aug 06, 2014

The Northern Territories in Canada is experiencing one of its worst fire seasons in history. As of this date, there have been 344 wildfires that have burned 2,830,907 hectares of land (close to 7 million ...

The volcano of a hundred thousand mouths

Jul 02, 2014

When the 1893 World's Fair opened in Chicago, fairgoers aboard the world's first Ferris wheel soared high enough to compare two cities: the White City—gleaming whitewashed architecture built for the massive ...

Safe water for the people in Tanzania

Jun 20, 2014

Hydraulic engineer Andrea Schäfer and photovoltaics expert Bryce Richards have developed a solar filtration system to produce high-quality drinking water from polluted brackish water and tested it successfully ...

Recommended for you

The Great Cold Spot in the cosmic microwave background

16 hours ago

The cosmic microwave background (CMB) is the thermal afterglow of the primordial fireball we call the big bang. One of the striking features of the CMB is how remarkably uniform it is. Still, there are some ...

Winter in the southern uplands of Mars

17 hours ago

Over billions of years, the southern uplands of Mars have been pockmarked by numerous impact features, which are often so closely packed that they overlap. One such feature is Hooke crater, shown in this ...

Five facts about NASA's ISS-RapidScat

17 hours ago

NASA's ISS-RapidScat mission will observe ocean wind speed and direction over most of the globe, bringing a new eye on tropical storms, hurricanes and typhoons. Here are five fast facts about the mission.

User comments : 0