On September 7, 1991, the costliest hailstorm (花暴) in Canadian history hit Calgary's southern suburbs. As a result, since 1996 a group of insurance companies have spent about $2million per year on the Alberta Hail Suppression Project. Airplanes seed threatening storm cells with a chemical to make small ice crystals fall as rain before they can grow into dangerous hailstones. But farmers in east-central Alberta — downwind of the hail project flights — worry that precious moisture (水分) is being stolen from their thirsty land by the cloud seeding.

Norman Stienwand, who farms in that area, has been addressing public meetings on this issue for years "Basically, the provincial government is letting the insurance companies protect the Calgary-Edmonton urban area from hail, " Mr. Stienwan d says, "but they're increasing drought risk as far east as Saskatchewan. "

The Alberta hail project is managed by Terry Krauss, a cloud physicist who works for Weather Modification Inc. of Fargo, North Dakota. "We affect only a very small percentage of the total moisture in the air, so we cannot be cousing drought. " Dr. Krauss says. "In fact, we may be helping increase the moisture downwind by creating wetter ground. "

One doubter about the safety of cloud seeding is Chuck Doswell, a research scientist who just retired from the University of Oklahoma. "In 1999, I personally saw significant tornadoes (龙卷风) form from a seeded storm cell in Kansas, " Dr. Doswell says. "Does cloud seeding create killer storms or reduce moisture downwind? No one really knows, of course, but the seeding goes on. "

Given the degree of doubt, Mr. Stienwand suggests, "it would be wise to stop cloud seeding. " In practice, doubt has had the opposite effect. Due to the lack of scientific proof concerning their impacts, no one has succeeded in winning a lawsuit against cloud-seeding companies. Hence, private climate engineering can proceed in relative legal safety.