We’ve been cloud seeding for decades, but now we finally know it works
On a cold winter day in Idaho in 2017, a light dusting of snow fell from the sky. For the first time, scientists are able to say with certainty that it fell because humans made it happen.
“We were really, really excited,” atmospheric scientist Katja Friedrich told Quirks & Quarks host Bob McDonald. “We got really hooked on this idea of, OK, we can do it one day, we can do it the next day.”
The team of researchers were testing cloud seeding, a technology designed in 1946 by chemist Vincent Schaefer, which involves infusing clouds with particles to turn lightweight water droplets into heavy droplets of rain or snow. Cloud seeding is used as a part of weather modification programs in countries around the world to attempt to do things like steering precipitation to drought-prone areas, or to enhance snowpack on ski hills. In Canada, it’s often used to try to lessen the impact of hailstorms.
But the problem is that until now, scientists hadn’t come up with a way to prove that cloud seeding actually worked outside of the lab.
“We had difficulties distinguishing what is generated naturally and what is generated by humans,” said Friedrich, an associate professor in the Department of Atmospheric and Oceanic Sciences at the University of Colorado Boulder.
This is the first time that scientists have definitively been able to accurately measure the amount of snow produced through cloud seeding. The researchers published their findings in the journal PNAS.
‘Nature usually does not produce zigzag lines’
Over three days in January 2017, the team of researchers tracked three separate cloud seeding events from start to finish. They used the “Doppler on Wheels” ground-based radar system, as well as the University of Wyoming’s King Air research plane, which is outfitted with radar and LIDAR systems to peer into atmospheric formations.
The research plane mapped the natural clouds first. Then, another plane flew through those clouds, using a series of flares to inject particles of silver iodide inside.
Immediately the researchers saw something strange in the clouds forming in the sky behind the seeding airplane.
“We suddenly saw these zigzag lines, and we were very puzzled because nature usually does not produce zigzag lines. So in this case we thought, OK these need to be seeding lines,” said Friedrich.
Seeing the same developments the second day confirmed their suspicions.
“The second day, we saw these same seeding lines, and on that day we could even see individual flares … and then we were totally hooked,” she said.
The team was able to watch as the liquid water inside the clouds turned into ice, and the snow started to fall. It wasn’t much — about a tenth of a millimetre of snow — but covering an area of 80 by 80 kilometres, that ended up being the water equivalent of 282 Olympic-sized swimming pools.
“At the beginning, we were not quite sure whether that is us and whether this is really from cloud seeding. But then once we could reproduce those results several times, then we actually got more confident,” she said.
“So if we hadn’t seeded the cloud there would not have been any precipitation on the ground.”
Cloud seeding is still a controversial technology for some.
“There are some potential downsides that we don’t think about too much,” Robert Jackson, Stanford University’s Earth Sciences Chair said in a 2017 interview on The Current. “One issue is where the rain would have fallen if you hadn’t cloud seeded. Does a cloud seeding event in Alberta keep a farmer in Saskatchewan from getting rain that he or she might have received?”
“So you’re extracting moisture from the atmosphere. That’s absolutely correct. However, these clouds would not precipitate in the area,” said Friedrich. “They can evaporate and maybe they fall down as precipitation over the ocean.”
“On the other hand, the snowpack in the mountains is really important, and millions of people and industries depend on this snowpack.”
She adds that in drought-stricken areas, every drop of water helps, even if that drop is human-made.
“I always say it depends on the cost of water. So if you’re in an area that’s very arid and dry and you’re under drought conditions, then every drop counts. So then why not do cloud seeding?”