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CLOUD

COMMUNICATIONPollution may harm our clouds

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CLOUD

COMMUNICATIONPollution may harm our clouds

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CLOUD

COMMUNICATION

Pollution may harm our clouds

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© Paul Lubianker 2015 All Rights Reserved

In dedication to Ilan Koren, planetary scientist at the Weizmann Institute of Science in Israel and lead author of the study, reached while en route to a Rolling Stones concert.

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INTRODUCTION BY ALINA BRADFORD

Pollution is the process of making land, water, air or other parts of the environment dirty and unsafe or unsuitable to use. This can be done through the introduction of a contami-nant into a natural environment, but the contaminant doesn’t need to be tangible. Things as simple as light, sound and temperature can be considered pollutants when introduced artificially into an environment.

Toxic pollution affects more than 200 million people worldwide, according to Pure Earth, a non-profit environmen-tal organization. In some of the world’s worst polluted places, babies are born with birth defects, children have lost 30 to 40 IQ points, and life expectancy may be as low as 45 years because of cancers and other diseases. Read on to find out more about specific types of pollution.

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TABLE OF CONTENTS

01 HOW DOES AIR POLLUTION AFFECT CLOUDS?

Aerosols are key in whipping up a cloud, a process that begins with the sun.

02 AEROSOLS Small particles suspended in the Earth’s atmosphere (aerosols) include fine aerosols such as pollution and smoke.

03 AIR POLLUTION CAN PREVENT RAINFALL

Urban and industrial air pollution can stifle rain and snowfall,

04 HERE COMES THE SUN: HOW THE WEATHER AFFECTS OUR MOOD

Weather will only influence us if we expose ourselves to it.

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HOW DOES AIR POLLUTION AFFECT CLOUDS?AEROSOLS ARE KEY IN WHIPPING UP A CLOUD, A

PROCESS THAT BEGINS WITH THE SUN.

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Deadening calm fills the Horse Latitudes, where there’s ocean, sky and little else. A satellite peers down, capturing wisps of cloud, counting particles suspended in the air, measuring rain-fall and monitoring weather. There is little wind. These latitudes, between 30 and 35 degrees away from the equator, are so calm that Spanish sailors in the 17th cen-tury could not move their heavily laden ships, or so the legend goes. So, the sailors dumped their cargo—horses—into the subtropical ocean and heaved on. But they left the place with a name: Horse Latitudes. These windless tracts have yielded a new hypothesis relevant to cli-mate science: Few clouds may have populated our skies before the Industrial Revolution, and pollutants spewed by factories since then may have vastly increased the cloudiness of our at-mosphere. The results were published yester-day in the journal Science.

The finding cuts to the heart of uncertainty con-tained in climate models today. Most scientists agree that humans are releasing massive quan-tities of carbon dioxide into the atmosphere and causing global temperatures to rise. But they disagree on the rate of warming. A doubling of CO2 concentrations could warm the planet by between 2 and 4.5 degrees Cel-sius, according to the Intergovernmental Panel on Climate Change (IPCC). Part of the uncer-tainty is due to clouds. They come in various shapes and types, as most people know—puffy popcorns (cumulus); loose brush strokes of mostly ice (cirrus); towering, dark monsters of thunderstorms (cumulonimbus) and many oth-ers. Clouds can either reflect the sun’s incom-ing rays back into space, cooling the Earth. Or they can act as a sheath and trap heat close to the Earth’s surface, warming the planet. Often, they do a little of both. And they do it incredibly well. Clouds have the ability to heat the planet much more than CO2, depending on the type of cloud, its geography and its altitude. And to make things more complicated, cloud particles can have various sizes, shapes and various traits. Translating these into predictions about the overall effect of clouds on the climate can be quite difficult.

THE ANSWER COULD HELP CLARIFY

HOW WARM CLIMATE CHANGE MIGHT GET

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AEROSOLSSMALL PARTICLES SUSPENDED IN THE EARTH’S ATMO-

SPHERE (AEROSOLS) INCLUDE FINE AEROSOLS SUCH AS POL-

LUTION AND SMOKE.

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Worldwide, most atmospheric aerosol particles are produced by ‘natural’ processes such as grinding and erosion of land surfaces resulting in dust, salt-spray formation in oceanic breaking waves, biological decay, forest fires, chemical reactions of atmospheric gases, and volcanic injection. Some par-ticles, on the other hand, have human origins—industry, agriculture, trans-port (including aviation), and construction. The composition of atmospheric aerosol particles varies widely depending on their source—they may contain salts (predominantly sulfates), minerals (such as silicon), organic materials, and, in most cases, water. The particles grow by absorbing water vapor and other gases. If the relative humidity is sufficiently high (usually about 80 percent or more), tiny water drops can form on some of the particles. A subset of these, called ‘cloud condensation nuclei,’ then grow into cloud drops, which eventually fall to the surface as rain or snow, depositing the particles on land or in the ocean. At higher altitudes, cloud ice particles form on some insoluble particles, such as dust. Although dust plumes from the Sahara and Gobi deserts can be seen circling most of the globe in satel-lite pictures, aerosol particles in the lower troposphere (the lowest layer of the atmosphere where weather occurs) are usually removed from the atmo-sphere by settling and precipitation within several days to weeks after they were produced. Their impacts, then, are fairly localized. In the stratosphere (the atmosphere layer above the troposphere), chemical reactions of gases from volcanoes produce sulfate particles that can remain for one or more years, spreading over much of the globe.

AEROSOL PARTICLES

AND CLIMATE

ALTHOUGH WE ARE FAMILIAR WITH LOCAL PARTICULATE ‘AIR POLLUTION’ DUE TO HUMAN ACTIVITIES, THE FACT THAT AT-MOSPHERIC PARTICLES OF BOTH NATURAL AND HUMAN ORI-GIN HAVE SUBSTANTIAL INFLUENCE ON OUR CLIMATE IS LESS WIDELY UNDERSTOOD.

AEROSOL SOURCES, COMPOSITION,

AND REMOVAL PROCESSES

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HOW IS HUMAN-CAUSED AIR POLLUTION

CHANGING OUR CLIMATE?

Human-caused particulate air pollution has a relatively minor—and likely decreasing—impact on our climate. Since aerosol particles of human origin both reflect and absorb solar energy as the solar beam travels down through the atmosphere, these particles can diminish the energy that arrives at the Earth’s surface as heat. Scientists estimate that particles produced by human activities have led to a net loss of solar energy (heat) at the ground (by as much as 8 percent in densely populated areas)[5] over the past few decades. This effect, sometimes referred to as ‘solar dimming,’ may have masked some of the late 20th century global warming due to heat-trapping gases.

SMALL PARTICLES SUSPENDED IN THE EARTH’S ATMOSPHERE (AEROSOLS) INCLUDE

FINE AEROSOLS SUCH AS POLLUTION AND SMOKE (RED) AND COARSE AEROSOLS

SUCH AS DUST AND SEA-SALT (GREEN). IMAGE SHOWS AEROSOL LEVELS ON APRIL

13, 2001 AS SEEN BY A NASA SATELLITE.

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AIR POLLUTION CAN PREVENT RAINFALLURBAN AND INDUSTRIAL AIR POLLUTION CAN STI-

FLE RAIN AND SNOWFALL,

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The new study, by Daniel Rosenfeld, of the Hebrew University of Je-rusalem, presents satellite images and measurements of “pollution tracks” downstream from major urban ar-eas and air pollution sources such as power plants, lead smelters, and oil refineries. The tracks consist of pol-luted clouds that have shut off virtually all precipitation because they contain abnormally small water droplets.

The droplets’ small size is caused by pollution particles that act as “seeding” sites around which cloud moisture condens-es. Approximately one million small droplets must col-lide and coalesce in order to make a precipitation-sized drop-that is, one large enough to fall below the cloud base and reach the ground before evaporating. In pol-luted clouds, there are too many small droplets and not enough larger ones. These small droplets float in the air with low probability of bumping into each other and merging into raindrops. The smaller droplets are also slower to freeze into ice crystals, resulting in less sleet and snowfall.

Because urban and industrial air pollution is a significant problem in many regions of the world, Rosenfeld’s findings suggest that human activity may be affecting rainfall patterns on a global scale. These data are the first direct evidence of how urban and industrial pollution affects rainfall levels, a question scientists have debated for several decades. In fact, some previous studies have concluded that air pollution might increase rainfall, but the debate has con-tinued due to a lack of convincing data.

URBAN AND INDUSTRIAL AIR POLLUTION CAN STIFLE RAIN AND

SNOWFALL, A NEW STUDY SHOWS,

BECAUSE THE POLLUTION PARTICLES PREVENT CLOUD WATER FROM CONDENSING INTO RAINDROPS

AND SNOWFLAKES.

HOT SMOKE

COLD SMOKE

WARM SMOKE

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WEATHER AND CLIMATE MODELS DON’T RECONSTRUCT THE

LIVES OF CLOUDS VERY WELL--ESPECIALLY STORM CLOUDS.

HOW POLLUTION IMPACTS STORM CLOUDS IN A BIG WAY

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As climate change continues, we may be in

for some heavier rain. Heavy rainfall events

have been increasing strikingly in the past 30

years and now, scientists have taken a closer

look at what might cause these events.

POLLUTION CAN AFFECT OUR CLIMATE IN MULTIPLE WAYS

BUT NOW, SCIENTISTS HAVE FOUND OUT THAT IT CAN ALSO

AFFECT THUNDERSTORMS.

IT TURNS OUT THAT POLLUTION CAUSES THUNDERSTORMS TO LEAVE BEHIND LARGER,

DEEPER, LONGER LASTING CLOUDS, WHICH MAY PLAY INTO CLIMATE WARMING.

Weather and climate models don’t reconstruct the lives of clouds very well--especially storm clouds. Usually, these models replace storm clouds with simple equations that fail to capture the whole picture. Because of these poor reconstructions, researchers have been unable to determine exactly why pollution causes anvil-shaped storm clouds to linger longer than they would in clean skies. More and smaller droplets can actually change things for the clouds. Scientists have long thought that smaller droplets start a chain reaction that leads to bigger, longer-lasting clouds. Instead of raining down, though, the lighter droplets carry their wa-ter higher, where they freeze. This freezing squeezes out the heat that the droplets car-ry with them and causes the thunder cloud to become draftier. The stronger convection then lifts more water droplets and builds up the cloud. Yet researchers don’t always see stronger convection in a polluted envi-ronment. In order to solve this mystery, the scientists compared real-life summer storm clouds to a computer model that zoomed deep into simulated clouds. The model in-cluded physical properties of the cloud particles as well as the ability to see convection. So what did they find? It turns out that in all cases, pollution increased the size, thickness and duration of anvil-shaped clouds. However, only two locations--the tropics and China--showed stronger convection. The opposite occurred in Oklahoma; pollution created weaker convec-tion. So what’s responsible? The researchers discovered that pollution resulted in smaller droplets and ice crystals, regardless of location. They also found that in clean skies, the heavier ice particles fall faster out of the anvil-shaped clouds, which causes the clouds to dissipate. However, the ice crystals in polluted skies were smaller and too light to fall out of the clouds, which made them last longer. In addition, it turns out that polluted clouds cooled the day and warmed the night, which decreased the daily temperature range.

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SUMMER TIME

WINTER TIME

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BIBLIOGRAPHYHOW DOES AIR POLLUTION AFFECT CLOUDS?

By Gayathri Vaidyanathan and ClimateWire

DOES AIR POLLUTION—SPECIFICALLY PARTICULATE MATTER

(AEROSOLS)—AFFECT GLOBAL WARMING?

Union of Concerned Science for a healty planet

AIR POLLUTION CAN PREVENT RAINFALL

American Association For The Advancement Of Science

HERE COMES THE SUN: HOW THE WEATHER AFFECTS OUR MOOD

The Conversation US PILOT