Ships crossing the Pacific Ocean emit particles into the clean air that create a seed for marine clouds. Image credit: NASAShips crossing the Pacific Ocean emit particles into the clean air that create a seed for marine clouds. Image credit: NASA

A new University of Washington study focuses on the idea of marine cloud brightening, which is being investigated by a UW group as a strategy to offset global warming. The strategy is to spray saltwater into the air to make marine clouds reflect more incoming solar rays. Small-scale tests of marine cloud brightening could help answer many scientific questions about clouds and aerosols. The goal for these geoengineering tests would follow the 2015 recommendations from the U.S. National Academies of Sciences that said any tests of geoengineering also yield scientific benefits.

"A major, unsolved question in climate science is: How much do aerosol particles cool the planet?," said lead author Rob Wood, a UW professor of atmospheric sciences. "A controlled test would measure the extent to which we are able to alter clouds, and test an important component of climate models."

The authors of this paper are part of a group that is proposing to spray salt water over oceans in order to cause a small increase in the brightness of marine clouds and boost the capacity to reflect sunlight. Doing this could be a short-term measure to offset global warming in a possible future emergency situation. It could further the understanding of our climate system.

The biggest problem in climate models is the clouds, which can reflect sunlight in unpredictable ways. Water droplets can only condense on airborne particles like smoke, salt or human pollution. When the air contains more particles, the same amount of moisture can form smaller droplets. This creates whiter, brighter and more reflective clouds. Climate scientists believe pollution since the Industrial Revolution has created brighter clouds that reflect more sunlight. This is offsetting the warming from greenhouse gases and traps long-wave radiation. They can’t pin down the size of the effect or predict how much it may change in the future.

"Testing out marine cloud brightening would actually have some major benefits for addressing both questions," Wood said. "Can we perturb the clouds in this way, and are the climate models correctly representing the relationship between clouds and aerosols?"

The proposal is waiting on funding to go further with this research. For years, UW researchers have been working with a group of engineers to develop a nozzle that will turn saltwater into tiny particles that could be sprayed high enough to reach the marine cloud layer. This is the first of many steps needed to implement the team’s three-year plan.

The researchers are proposing to produce a sprayer that can eject trillions of aerosol particles per second and conduct lab tests of the sprayer. They also want to do preliminary outdoor tests in a coastal area that is flat, free of air pollution and prone to marine clouds. Finally, they want to move small-scale offshore tests, if the original tests were successful. People may someday decide whether to use a scaled-up version to create a small increase in reflection of sunlight over the oceans.

Along with the paper on the scientific benefits of cloud brightening, the team of UW graduate students and professors has published a paper on what specific measures would need to be taken for successful cloud brightening test evaluation.

To learn more about this paper and research, click here.