Cloud Falls on China's Claim to Stop Rain
Live Science ^ | 04/22/08 | Andrea Thompson
Andrea Thompson
LiveScience Staff Writer
LiveScience.com
Jeremiah 10:12-14 He hath made the earth by his power,
he hath established the world by his wisdom, and hath stretched out the heavens
by his discretion. When he uttereth his voice, there
is a multitude of waters in the heavens, and he causeth
the vapours to ascend from the ends of the earth; he maketh lightnings with rain, and bringeth forth the wind out of his treasures. Every man is
brutish in his knowledge: every founder is confounded by the graven image: for
his molten image is falsehood, and there is no breath in them.
China's plans to force Mother Nature's hand with
"cloud seeding" and keep rains at bay during the start of the Olympic
Games this August may be all wet, one scientist said today.
"I'm very skeptical about what they claim
they can do," said Roelof Bruintjes,
the lead researcher for U.S. National Center for Atmospheric Research in
Chinese officials will reportedly try to force the
rain out of the clouds before the opening ceremony through a process called
cloud seeding to clear the smog-filled skies and keep the rain from drenching
the athletes and spectators.
More than 40 countries are currently conducting
over 150 projects, with more than 60 projects being run in
Growing crystals
Cloud seeding is done by artificially enhancing
the processes that form water droplets and ice crystals in clouds. Droplets and
crystals needs a surface to form on, which is usually provided by tiny aerosol
particles (whether naturally-formed or from pollution) in the atmosphere.
"Every droplet, every ice crystal forms on a
particle," Bruintjes said.
To seed a cloud, scientists inject particles into
an existing cloud for the water to coalesce on or ice crystals to grow on. One
of the methods most commonly used is the injection of silver iodide into the
cloud - these crystals have the same structure as ice crystals and so can
readily grow them on their surfaces.
But a cloud must already exist before scientists
can seed the atmosphere.
"We can not make clouds, we cannot chase away
clouds," Bruintjes said.
Bruintjes is skeptical of
"There is no evaluation, there is no
scientific literature available that can substantiate their claims," he
said.
The studies that have shown the most success in
cloud seeding have been done in winter clouds to increase snow pack in mountain
regions, said Arlen Huggins of the Nevada State Weather Modification Program.
One such studied showed that seeding can increase ice crystal formation and get
an annual increase of approximately 10 percent in snowfall under the right
conditions, he said.
Inadvertent seeding
Measuring the effect of cloud seeding can prove
difficult because seeding not only affects the physical processes within the
cloud, but also the cloud's lifetime, specifically, "how long the cloud
will be raining," Bruintjes said.
Cloud seeding may also work differently in
different regions and under different atmospheric conditions - what may work in
an unpolluted region may not in a highly polluted one.
"What we know now is that cloud seeding may
not work the same on a day-to-day basis, a season-to-season basis," Bruintjes added.
Another matter complicating cloud seeding is that
pollution artificially seeds clouds everyday. If you drove your car to work
today, "you have in effect been cloud seeding," Bruintjes
said.
In fact, pollution has been blamed for the loss of
snow pack in regions that depend on clouds that form over mountains.
"Pollution over the last few decades has
caused a systematic decrease in snow pack in those regions over the past few
decades," said Joe Golden, with the National Oceanic and Atmospheric
Administration
But recent studies have shown that strategic
seeding can reverse that trend and increase the snow pack where it's needed, he
noted.
Golden also said it is time to re-open federal
programs that look into weather modification because new technologies have come
along that better enable researchers to look at the
effects of cloud seeding in the clouds themselves.
Bruintjes said that while