Atmospheric particles can brighten cold clouds as well as warm ones

December 5, 2014
The paper is included in a special issue of Philosophical Transactions of the Royal Society A, compiled and edited by John Latham, NCAR; Philip J. Rasch, PNNL; and Brian Launder, University of Manchester. Cover image courtesy of the journal.

For the first time, modeling research led by Pacific Northwest National Laboratory found that atmospheric particles can brighten cold clouds in the Arctic. Using simulations, they showed that low clouds over the Arctic may be brightened by deliberately injecting small particles known as aerosols. It's already well known that injecting aerosols into low clouds over the warm ocean can, in some circumstances, reduce the amount of sunlight that reaches the surface. The concept, untested over the Arctic until now, is called marine cloud brightening, and it can also happen when ships send exhaust into the atmosphere.

The modeling simulations by PNNL and collaborators at the National Center for Atmospheric Research (NCAR) and the National Oceanic and Atmospheric Administration (NOAA) used computer modeling to show that Arctic cloud brightening could have considerable local , but likely would not substantially alter the global energy balance.

Propositions to shoot sea salt or other tiny particles into low clouds over the ocean have been tested in computer models over temperate regions. Brighter clouds reflect more of the sun's energy back into space, shading and cooling the surface. The concept would amp up a process that happens naturally when sea spray is lofted into the atmosphere from ocean waves. The research team wanted to know, would the same concept work over the Arctic? The answer could matter for the climate, if geoengineering techniques—proposed by some as a temporary way of reducing the climate effects of greenhouse gases while mitigation is in progress—are ever put into practice.

PNNL researchers and their collaborators used the Weather Research and Forecasting Model (WRF), a leading community atmospheric model that can resolve clouds and represent many of the complex microphysical interactions between clouds and aerosols. They ran eight cases, in clean to polluted atmospheres, and simulated injection of into the atmosphere. Their simulations showed the particle impacts in a wide variety of background conditions.

In this study, the researchers looked at idealized cases. For example, they did not allow for initial wind, which would blow clouds and particles around, although wind was allowed to develop over the course of the simulation. But the Arctic is windy, so how did that choice affect the results? What happens if the wind blows the particles across the entire simulation area and doesn't keep them in a straight line? The next few studies will look at the impacts of these and other research assumptions.

"This work is also relevant if Arctic sea ice melts and more ships pass through the Arctic," said Dr. Ben Kravitz, atmospheric scientist at PNNL and lead author. "Because ship plumes—instigated by particles from diesel engine exhaust—can also generate trails of bright clouds."

Explore further: Brightening clouds: Atmospheric scientists evaluate a technique for reflecting more sunlight back to space

More information: Kravitz B, H Wang, PJ Rasch, H Morrison, and AB Solomon. 2014. "Process-Model Simulations of Cloud Albedo Enhancement by Aerosols in the Arctic." Philosophical Transactions of the Royal Society A 372(2031). DOI: 10.1098/rsta.2014.0052

Related Stories

Tagging tiny particles in turbulent clouds

May 30, 2014

(Phys.org) —Hitching tiny atmospheric particles to cloud formation enables climate models to represent the particles' effects on convective storm systems. Scientists at Pacific Northwest National Laboratory and collaborators ...

Recommended for you

Scientists warn that saline lakes in dire situation worldwide

October 23, 2017

Saline lakes around the world are shrinking in size at alarming rates. But what—or who—is to blame? Lakes like Utah's Great Salt Lake, Asia's Aral Sea, the Dead Sea in Jordan and Israel, China's huge Lop Nur and Bolivia's ...

Mountain glaciers shrinking across the West

October 22, 2017

Until recently, glaciers in the United States have been measured in two ways: placing stakes in the snow, as federal scientists have done each year since 1957 at South Cascade Glacier in Washington state; or tracking glacier ...

Carbon coating gives biochar its garden-greening power

October 20, 2017

For more than 100 years, biochar, a carbon-rich, charcoal-like substance made from oxygen-deprived plant or other organic matter, has both delighted and puzzled scientists. As a soil additive, biochar can store carbon and ...

Cool roofs have water saving benefits too

October 20, 2017

The energy and climate benefits of cool roofs have been well established: By reflecting rather than absorbing the sun's energy, light-colored roofs keep buildings, cities, and even the entire planet cooler. Now a new study ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

alchemist from bristol
5 / 5 (1) Dec 05, 2014
Switching to renewable energy will stimulate the economy, create jobs, save money and clean up the environment. "Carbon dioxide has increased about 40 percent in the atmosphere since the 1750s, due to pollution from dirty energy like coal, oil, and gas. The result is a warming climate." http://clmtr.lt/c/QAu0cd0cMJ

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.