Somewhere nearby, at the headquarters of WeatherMod Inc, a group of technicians are busily checking data, confident that their efforts have worked. They have been in contact with two pilots who have just completed their spray sorties and are returning to land at Heathrow’s new third runway.
Thanks to the delivery of four kilograms of, in its pure form, a yellowish powder known as Silver Iodide (AgI) into clouds upwind of London, it is now raining over the Salisbury Plain, 100 miles away, and the rain predicted for later in SW19 is now 92% less likely.
But two questions need further investigation to consider the likelihood of the above scenario at Wimbledon: can we do it (that is, does it work) and should we do it? Neither, it turns out, are particularly easy to answer.
Changing the weather
In order to make rain several processes need to occur. First, small particles known as cloud condensation nuclei (CCN) are required onto which water can condense. Then these droplets need to grow to a size where they precipitate out of the cloud, finally falling where and when required.
In our hypothetical scenario we would therefore need to be able to either control or at least predict accurately the concentration of CCN, the rate at which droplets form, and the evaporation rates within the clouds. We’d also also need to have some handle on the rate and direction in which rain would fall.
One of the major drawbacks of cloud seeding is a lack of proof that it works: given weather forecasting remains imperfect, how would you know what would have happened without intervention? The second part of the question is arguably even harder to approach. What are the ethics of removing water from one part of the world, even on a small scale, and moving it somewhere else? Is this “messing with nature” or “playing God”? Water is, after all, the most precious commodity on Earth.
Deliberate and accidental effects from commercial activity also seem possible. That dreamy, rain-free wedding ordered up by an anxious billionaire could easily ruin a school sports day in a nearby town.
It’s certainly possible in theory to prevent rain in one place by using cloud seeding to induce it in another, upwind. But there are huge challenges and the jury is still out about whether such efforts really work.
There are some very good causes, such as inducing rainfall in Sub-Saharan Africa during drought, where I would sanction intervention. For something as frivolous as a sporting event I feel differently. Just last weekend I played cricket for four hours in unrelenting drizzle (thanks Skip). While not a massively enjoyable experience it was at least familiar, and is part of the essence of both cricket and tennis. There’s some comfort in that.