From Inside Climate News (Bob Berwyn):

New research supports seeding efforts to bolster water supplies in drying regions, but some scientists question its effectiveness in addressing climate change.

Winter bonfires paying homage to snow gods have long been a tradition in cold weather regions around the world.

But in the last 70 years or so, communities in the western United States have gone beyond rituals and added a technological twist. Across hundreds of mountaintops, from the Sierra Nevada to the Sawtooths, Wasatch and Colorado Front Range, cloud seeding experts are now often burning small amounts of silver iodide with the aim of bolstering dwindling water supplies.

The vaporized metal particles are ideal kernels for new ice crystals. When moist, super-cooled air rises over mountain ranges under predictable winds, it sets up perfect conditions for the crystalline alchemy that creates snow, the white gold craved by ski resorts, ranchers and farmers and even distant cities that need mountain water to survive.

The scramble for water has intensified as global warming has battered much of the West during the last 20 years with heat waves, droughts and wildfires. With projections for declining snowpack and river flows, cloud seeding is becoming a regional climate adaptation measure costing several million dollars each year. In other regions, including parts of the central United States, seeding has also been used to try and enhance summer rains and to reduce the risk of severe hail storms.

Still Controversial

But even as governments and businesses increase the practice, questions remain about how effective it is, and some leading climate scientists say it should not be seen as a meaningful response to climate change. Though cloud seeding has expanded to cover tens of thousands of square miles across the West, there are no recent comprehensive studies assessing the effects in both targeted and non-targeted areas. Cloud-seeding permits are issued under a patchwork of state and federal rules, which sometimes cuts the public out of the process.

Several panels at a recent conference on weather modification addressed some of those issues, and included presentations on how efforts to cooperate on regional cloud seeding projects could serve as a model for governance of even larger scale climate-mitigating geoengineering projects.

Some elected officials and water experts say the money is well spent because it produces millions of gallons of water that can be stored and used during drier and hotter summers, when stream flows dwindle. Scientific studies in the last few years show that cloud seeding works during suitable weather patterns that are already conducive to snowfall.

In the winter of 2018-2019, water managers in Colorado said their central mountains cloud seeding program produced between 80,000 and 90,000 acre feet of water at a cost of $2.70 per acre foot—a bargain in a region where prices per acre foot can reach $30,000. An acre foot of water is 325,851 gallons, enough for two average Colorado families for a year…

Research in the last two decades proves that the physical process works, but it’s still not clear how much water it produces. At best, the latest studies “hold promise for narrowing the uncertainty” that has accompanied such research over its long history, the paper concluded.

Altering clouds with plumes of metallic smoke might work on a localized basis, but it isn’t the right solution for large-scale and long-term regional drying and warming, said atmospheric scientist Kevin Trenberth, with the National Center for Atmospheric Research and the University of Auckland, in New Zealand.