MALAYSIA – Ever year during the dry season in Southeast Asia, Malaysia is covered with smog. The smoky haze is so irritating residents are forced to wear face masks. The smog blows in from Indonesia, where fires are used to clear land for palm oil and paper plantations.
This year, the fires are particularly bad, to the point where the Malaysian government is prepared to generate rain by seeding clouds. Gary Theseira, the special functions officer in the environment ministry, said “the moment the cloud situation is right, the chemicals will be loaded and the aircraft will take off and proceed with the seeding.”
Here’s how cloud formation normally works: water condenses around microscopic aerosol particles, and a cloud is born. Aerosols are airborne minuscule liquid droplets or tiny solid particles. Without these particles, extremely cold temperatures and high relative humidity is required. Clouds would be much rarer.
However, only certain aerosols are good for cloud formation. These aerosols, called ice-nucleating particles, allow ice to form at higher temperatures, which then creates clouds. Certain ice-nucleating particles can help seed rain.
Natural sources of aerosols include sea spray, wind-blown dust and microbes. Humans also produce aerosols from smoke and other pollution. Both natural and anthropogenic aerosols can serve as ice-nucleating particles, with varying effectiveness.
Seeding clouds artificially generates rain by providing suitable particles for ice nucleation. Silver iodide, potassium iodide or dry ice is sprayed from a plane. The particles disperse and can produce rain.
This technique has been used for decades for various purposes, from creating more snow for ski resorts and hydroelectric power stations to reducing fog around airports and shrinking the size of hail. However, there is no scientific consensus on the efficacy of seeding clouds.
Not much is known about ice-nucleating particles and their global distribution, nor the impact human activities will have on cloud formation in the future. Scientists are moving towards more controlled experiments to tease apart the effects and to move forward in our understanding of ice-nucleating particles and other atmospheric aerosols.