Third Grade
Worksheets
Seeding the Clouds
People depend on rain. We need water to drink. We need water to grow our food. We use water to make some of our electric power. We use it for boats to move supplies from place to place. We bathe in it. We swim in it. For thousands of years, people have depended on the weather. Now people are looking for ways to control weather.
Since the late 1940s, scientists have been using cloud seeding. Storm clouds must already be in the air for cloud seeding to work. Then chemicals such as silver iodide crystals are sprayed into the clouds. Sometimes propane or dry ice is used. The chemicals cool the cloud. This causes the water vapor to condense. Rain falls. Seeding the clouds causes more rain to fall than would have fallen without using the chemicals.
Cloud seeding can be done from the ground. Canisters of chemicals can be shot out of anti-aircraft guns. Chemicals can be sprayed from machines on the ground. Airplanes and sometimes rockets are also used to spray the chemicals into clouds from the air.
