JUN 19, 2014 12:00 AM PDT

How Do Humans Affect Clouds

WRITTEN BY: Ilene Schneider
Understanding how clouds affect the climate is a difficult proposition. What controls the makeup of the low clouds that cool the atmosphere or the high ones that trap heat underneath? How does human activity change patterns of cloud formation? The research of the Israel-based Weizmann Institute's Prof. Ilan Koren suggests that we may be nudging cloud formation in the direction of added area and height. He and his team have analyzed a unique type of cloud formation; their findings, which appeared recently in Science, indicate that in pre-industrial times, there was less cloud cover over areas of pristine ocean than is found there today.

In order to form clouds need tiny particles called aerosols that rise in the atmosphere. These aerosols - natural ones like sea salt or dust, or such human-made ones as soot - form nuclei around which the cloud droplets condense. In relatively clean environments, clouds can only grow as large as the amount of aerosols in the atmosphere allows. They are the limiting factor in cloud formation.

The question is: Does the current load of aerosols in the atmosphere already exceed that limit, in which case adding extra particles should not greatly affect cloud formation, or do they continue to be a limiting factor as pollution rises, so that added aerosols would continue to influence the clouds? A model developed by Koren and his team showed that an increase in aerosols, even in relatively polluted conditions, should result in taller, larger clouds that rain more aggressively. But proving the model was another story: Experimenting on clouds, or even finding ways to isolate the various factors that go into their formation in real time, is a highly difficult undertaking.

Koren, research student Guy Dagan and Dr. Orit Altaratz in the Earth and Planetary Sciences Department looked to an unlikely place to test their model: near the horse latitudes. These are subtropical regions far out in the oceans that were reviled in the past by sailors because the winds that carried their sails would die out there for weeks on end. Here was a lab for them to test the basic physics of their model: an atmospheric region controlled by well-defined meteorological conditions, which was sometimes pristine, sometimes containing low levels of aerosols. If the model was correct, transitions from one to the other should be dramatic. And they wanted to test their theory on the clouds that do form in this region - warm convective clouds that are fuelled by the ocean's moisture.

With other potential factors - wind, large temperature swings or land formations - out of the way, the team could concentrate on the aerosols, comparing daily satellite images of cloud cover and measurements of the aerosol load to the predictions of the model. Using many different types of analysis, they found that their model closely matched the satellite observations.

They then looked at another source of data: that of the Clouds' and the Earth's Radiant Energy System (CERES) satellite instruments which measure fluxes of reflected and emitted radiation from the Earth to space, to help scientists understand how the climate varies over time. When analyzed together with the aerosol loading over the same area at the same time, the outcome, says Koren, was a "textbook demonstration of the invigoration effect" of added aerosols on clouds. In other words, the radiation data fit the unique signature of clouds that were growing higher and larger. Such clouds show a strong increase in cooling due to the reflected short waves, but that effect is partly cancelled out by the enhanced, trapped, long-wave radiation coming from underneath.

At least over the oceans, the pre-industrial cloud conditions would have been considerably different from those of today; this implies that the aerosols we have been adding to the atmosphere may have had a significant effect on global patterns of cloud formation and rain.

According to Koren, "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. 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."

Prof. Ilan Koren's research is supported by the J & R Center for Scientific Research; and the estate of Raymond Lapon.
About the Author
  • Ilene Schneider is the owner of Schneider the Writer, a firm that provides communications for health care, high technology and service enterprises. Her specialties include public relations, media relations, advertising, journalistic writing, editing, grant writing and corporate creativity consulting services. Prior to starting her own business in 1985, Ilene was editor of the Cleveland edition of TV Guide, associate editor of School Product News (Penton Publishing) and senior public relations representative at Beckman Instruments, Inc. She was profiled in a book, How to Open and Operate a Home-Based Writing Business and listed in Who's Who of American Women, Who's Who in Advertising and Who's Who in Media and Communications. She was the recipient of the Women in Communications, Inc. Clarion Award in advertising. A graduate of the University of Pennsylvania, Ilene and her family have lived in Irvine, California, since 1978.
You May Also Like
SEP 01, 2020
Chemistry & Physics
No Child's Play - Advanced Bubble Manipulation Method can Transform Chemical Processing
SEP 01, 2020
No Child's Play - Advanced Bubble Manipulation Method can Transform Chemical Processing
Gas bubbles are fascinating, playful objects in children's eyes. In fact, they play an essential role in many indust ...
SEP 04, 2020
Microbiology
Researchers Discover a Way to Use Microbes to Help Make Plastic
SEP 04, 2020
Researchers Discover a Way to Use Microbes to Help Make Plastic
Researchers have discovered that some bacteria can make ethylene in a way we never knew about; microbes that metabolize ...
SEP 29, 2020
Earth & The Environment
Using native wild species to improve crop breeding and production
SEP 29, 2020
Using native wild species to improve crop breeding and production
New research from the University of Portsmouth and Royal Botanic Gardens, Kew, highlights the concern that global farmin ...
OCT 23, 2020
Chemistry & Physics
The Ever-Evolving Battle to Fight Corrosion in Nuclear Reactors
OCT 23, 2020
The Ever-Evolving Battle to Fight Corrosion in Nuclear Reactors
Since its birth in the early 20th century, atomic research has brought mostly positive impacts to our lives. This week i ...
OCT 28, 2020
Earth & The Environment
How detective geologists are tracing illegal sand
OCT 28, 2020
How detective geologists are tracing illegal sand
To most of us, sand is something that we likely only think about while at the beach. But for people who build things, es ...
NOV 13, 2020
Earth & The Environment
What the cylones of the past can tell us about the cyclones of the future
NOV 13, 2020
What the cylones of the past can tell us about the cyclones of the future
Research from the Woods Hole Oceanographic Institution (WHOI) has reconstructed the patterns of historical tropical cycl ...
Loading Comments...