Who'll start the rain? By Suzanne Bopp

Aug. 6, 2008 | This week, days before Friday's opening ceremony of the Beijing Olympics, cannons and rocket launchers by the thousands will be trained on the Chinese skies. In the cross hairs: the clouds.

This is latest of China's many efforts to control the weather. China is probably the world's largest practitioner of cloud seeding, spending about $90 million a year. Last April, it claimed a major weather victory after seeded clouds deposited a centimeter of snow on the Tibetan mountains. Now, eager to ensure rain comes before -- not during -- the Olympics, the Beijing Weather Modification Office plans to seed the clouds that float by beforehand, hoping to wash the pollution from the air and wring out any event-delaying precipitation.

But U.S. scientists are skeptical. "China is promising something they can't deliver," says Bruce Boe, director of meteorology for Weather Modification Inc., a Fargo, N.D.-based company. "To alter a cloud's aerosols in such a dramatic way that it won't rain -- the cost will be extreme, and I don't know how to do it confidently. Nature is so large and powerful it can always overwhelm you." China has no scientific evaluations to support its promises. And, he says, it's just not possible to exercise such precise control over the weather.

Whether or not it's possible to exercise any control at all over the weather remains subject to debate. While countries around the world -- including the United States -- continue to fund cloud seeding in drought-stricken regions desperate to refill reservoirs or water crops, the efforts have been beset with failures and few successes since the very first clouds were treated.

That was in the 1950s, near the New York labs of General Electric, following the discovery that dry-ice shavings could convert super-cooled (colder than freezing) water droplets to ice crystals. That mattered because clouds need ice crystals (or some kind of small particles ) to form precipitation. Cloud seeding tries to fill that need. Today silver iodide -- its structure mimics that of ice crystals -- is most commonly used in a method called glaciogenic cloud seeding.

Another method, hygroscopic cloud seeding (which some scientists say holds the most promise today), uses materials such as salt to provide a droplet-attracting nucleus; it can be used in warmer clouds. Both methods, whether dispersed through planes or rocket launchers, need to start with a cloud; they can't create clouds. Cloud seeding is more like cloud fertilizing: It tries to make a cloud a more efficient producer of rain or snow.

After the discovery at GE, the company hired a plane to release dry ice into clouds during the winter of 1946. On the final day of the experiment, Schenectady, N.Y., had its heaviest snowfall of the season, causing GE to worry about the legal liabilities of changing the weather.

The initial promise of the discovery was quickly swamped by disillusionment. "People had all kinds of immediate aspirations that they could control the weather," Boe says. "But there was a lot of overselling. If your town had a drought, people would show up and try to sell this, then get out of town fast if it didn't work. That did a lot of damage to cloud seeding's reputation. Worldwide, that still happens."

While dozens of foreign countries -- Mali, Burkina Faso, Saudi Arabia, Indonesia and Australia, to name a few -- continue to try to get the weather they want, the U.S. hangs back slightly. "In other countries, you don't have people sitting around saying, 'We're not sure this works,'" Boe says.

In America, that refrain is heard frequently, but cloud seeding continues on the order of 60-some projects in 10 Western states a year, funded mainly by local and county governments, agricultural interests and, occasionally, ski resorts. Although the American Meteorological Society says some studies have shown a 10 percent increase in rain volume, the National Academy of Sciences has said there is no conclusive evidence that cloud seeding works.

It's not the initial cloud-seeding equation that is in doubt: Silver iodide does produce ice crystals in clouds. "You can see on a radar how it grows to larger particles," says Dan Breed, a project scientist with the National Center for Atmospheric Research. "But the chain of events between that and precipitation hitting the ground is much more complicated."

Some clouds, it turns out, are less complicated than others. Winter orographic clouds, which form over mountains in winter, are simpler to work with than convective clouds, which cause thunderstorms. Orographic clouds occur almost every day in the Western mountains, where shortages of winter snowpack (needed to fill lakes, rivers and reservoirs in the spring) mean extra precipitation is most often needed.

Glaciogenic seeding is also used for hail suppression; by providing many ice particles for hail to form around, it prevents very large hail from developing. But hailstorms are extremely complicated, Breed says, and experiments with hailstorms are risky. "You do a project or experiment and you can end up with insurance claims or crop damage," he says.
In Calgary and Red Deer, Alberta, insurance companies are the ones that have funded a hail suppression project for more than a decade, in an effort to reduce their damage claims. The fact that they are spending a couple million dollars a year on this program should be taken as proof that cloud seeding works, says Don Griffith, president of North American Weather Consultants, a Sandy, Utah-based weather modification company.

For insurance companies, and many other funders of cloud seeding, the chance of success is worth the money. That's what drove the $8.8 million cloud-seeding project in Wyoming, initiated in part by dry local irrigation districts. Scientists found funding to piggyback research on the project, but the whole thing has hit early stumbling blocks, thanks to its proximity to designated wilderness areas.

To environmentalists, wilderness areas should be protected from such intrusions. "The most defining concept in the Wilderness Act is 'untrammeled by man.' The idea behind cloud seeding is anathema to that," says George Nickas, executive director of Wilderness Watch. "It's hard to envision something more offensive to the idea of wilderness." In fact, the Forest Service's own regulations command, "Do not permit long-term weather modification programs that produce, during any part of successive years, a repeated or prolonged change in the weather directly affecting wilderness areas."

Nevertheless, the project has proceeded, with minor modifications: The silver-iodide-releasing generators are to be placed outside, not inside, the wilderness areas. That's not a satisfying solution for the protesters -- it will still introduce more pollution.

"Under that same logic, if I wanted to dispose of toxic waste, I could do so to my heart's content on Forest Service lands as long as I dumped the stuff out of an airplane instead of packing it in on horseback," Jonathan Ratner, Wyoming director of the Western Watersheds Project, wrote in a statement. Part of his concern is what would come with increased rainfall over the forest -- increased pollution. Rampant gas and oil development in Wyoming has raised emissions several-fold; rain could bring that out of the sky into the water and cause nitrification.

Neither protests nor the deep discomfort about changing the weather has translated to a glut of weather-modification-related lawsuits. No doubt that's partly due to the fact that a plaintiff seeking damages would have to prove the cloud seeders were responsible for the harmful weather, and causation is as difficult to prove for attorneys as for scientists. It's not uncommon to hear the complaints that someone's cloud seeding stole someone else's rain. But scientists point out that that's also impossible to prove.

A bigger worry is that cloud seeding might be having the wrong effect. "Right now there's no guarantee, but we might be spending time and money and reducing precipitation," says Colorado State University atmospheric science professor William Cotton.

U.S. funding for research to answer such questions remains paltry. Down from a high in the late 1970s of $20 million, today less than $500,000 goes to cloud-seeding studies. Because studies are lengthy -- it takes about 10 years to look at weather trends -- even those that get funding often run out before the study is complete. Bills currently moving though Congress seek to establish a national weather-modification program, but such bills have been introduced, and disappeared, before.

This time around, there may be renewed interest, courtesy of climate change, which presents some of the same fundamental questions as weather modification. Scientists are more interested than ever in learning how we're already changing our weather, perhaps to learn how to change it back.

It seems certain we've altered precipitation patterns in measurable ways. "We're finding aerosol pollution reduces precipitation in orographic clouds," Cotton says. "It introduces very small particles, and they all compete for the same amount of water. Pollution means huge numbers of particles, so it's hard to go in and seed clouds that are polluted."

Over the past few decades, pollution seems to have decreased precipitation considerably, especially in the West, where clean ocean air passes over polluted urban areas before moving inland. In the Sierra Nevada mountains, the loss is estimated at 3.2 million acre feet (an acre foot covers an acre of land in water 1 foot deep) each year.

Can we learn to seed polluted clouds so we can get that precipitation back? What about the effects of changing temperature? We know low clouds tend to have a cooling effect on earth, and high clouds create warmth by absorbing more long-wave radiation. Could we use some of these effects to alter not just the weather but the climate itself?

Such climate engineering could be the next hot topic among atmospheric scientists. "We may have no choice," Cotton says. "Twenty years down the road, if the warming trend has increased enormously and half of Florida is underwater, politicians will say, 'Do climate engineering.' Doing something is better than sitting on your hands. If, at that point, we don't have the scientific knowledge, and we introduce the technology, we could find ourselves in the middle of an ice age. We won't be able to figure this out that fast."

Attempting such a strategy would raise all of cloud seeding's questions -- of control, unintended consequences, environmental effects -- to a new order of magnitude. But we need to start looking at it now, Cotton says. "If politics take control, and we don't have a science basis, who knows what could happen?"

http://www.salon.com/env/feature/2008/08/06/cloud_seeding/index.html