Cloud seeding. Does it work?

[lionking]

On a flight back from Adelaide, South Australia, tonight I sat next to a person I had never met before who is a physicist and mathematician who also happens to be one of the few cloud seeders in Australia, and possibly the world. He told me about his job of flying into large clouds in Tasmania in a light plane, seeding them with silver oxide and measuring and examining the results. We also spoke about his visits to CERN, the Smithsonian and other very interesting topics (he was by far the most interesting person I have sat next to on a flight).

But the point of this thread is that he contends that the work he does has resulted in a conservative 5% increase in rainfall in that state. I should add that the main interest in increasing rainfall is not for drinking water or irrigation (there is more than enough for that) but hydroelectricity.

I have looked up wikipedia about this, and it was ambivalent about the effectiveness of cloud seeding. Does anyone have an opinion on this topic?

 

[Cainkane1]

Tell him he needs to fly to Georgia USA. We are suffering a 20 year rain deficite.

 

[Wildy]

No, he's needed in South Australia.

 

[Cuddles]

I have looked up wikipedia about this, and it was ambivalent about the effectiveness of cloud seeding. Does anyone have an opinion on this topic?

From what I've read, it's far from certain but it does seem to work at least a bit. Theoretically, there's nothing wrong with it at all. Rain forms around nucleation centres, usually dust and similar, so putting more of them in a cloud causes more rain to form.

As far as I can tell, the main problem is simply that it is extremely hard to test. Since we can't predict the weather all that reliably, and are even worse at predicting short term climate variation, it is almost impossible to tell if you actually get more rain than you would have otherwise. While a lot of the research looks promising, an awful lot of it also looks like simply afirming the consequent, forgetting the misses and regression to the mean - essentially a placebo effect. For example, if you have a drought then try cloud seeding and get rain, does that mean that the cloud seeding caused the rain, or simply that the drought would have ended anyway? There are plenty of examples where cloud seeding appears to have worked, but there are also many where it didn't. It seems very possible that there are a lot more times it didn't work that we simply don't hear about, and that what appears to be a correlation is in fact no such thing.

I wouldn't be at all surprised if cloud seeding really does work. After all, it is based on some fairly simple known physics. However, I don't think the evidence supports its use yet. There are consequences from spraying large amounts of silver into the atmosphere, and there just don't seem to be adequate risk assessments or evidence of a benefit to justify doing so on the scale that currently occurs, let alone on a larger scale.

 

[Skwinty]

Back in the 80's when I was working in the aviation industry, I had the opportunity to spend a few hours in a Lear jet seeding cumulous clouds with I think magnesium oxide. This was done on behalf of the tobacco farmers to prevent hail. Hail was a common occurence which caused huge damage to the crop.

It was quite successfull and hugely expensive. Every few months the Lear had to have all leading edges and cockpit windscreen replaced due to hail damage.

There was lots of opposition from the non tobacco farmers who felt the maize crops were being polluted.

 

[dudalb]

It's not woo in that it has a solid scientific basis, but it is not very reliable. It "works" at times, but not enough to make it something you really want to depend on to get your crops watered.

 

[lionking]

From what I've read, it's far from certain but it does seem to work at least a bit. Theoretically, there's nothing wrong with it at all. Rain forms around nucleation centres, usually dust and similar, so putting more of them in a cloud causes more rain to form.

As far as I can tell, the main problem is simply that it is extremely hard to test. Since we can't predict the weather all that reliably, and are even worse at predicting short term climate variation, it is almost impossible to tell if you actually get more rain than you would have otherwise. While a lot of the research looks promising, an awful lot of it also looks like simply afirming the consequent, forgetting the misses and regression to the mean - essentially a placebo effect. For example, if you have a drought then try cloud seeding and get rain, does that mean that the cloud seeding caused the rain, or simply that the drought would have ended anyway? There are plenty of examples where cloud seeding appears to have worked, but there are also many where it didn't. It seems very possible that there are a lot more times it didn't work that we simply don't hear about, and that what appears to be a correlation is in fact no such thing.

I wouldn't be at all surprised if cloud seeding really does work. After all, it is based on some fairly simple known physics. However, I don't think the evidence supports its use yet. There are consequences from spraying large amounts of silver into the atmosphere, and there just don't seem to be adequate risk assessments or evidence of a benefit to justify doing so on the scale that currently occurs, let alone on a larger scale.

On the silver in the atmosphere issue (and it is silver iodine, not oxide) the scientist I sat next to told me that they use a total of about 1 kilogram per year and that it would be measured, if at all, in the parts per trillion. In any case, he said, a person can in fact ingest a large amount of silver with no ill effects.

 

[gnome]

I could see a potential problem even if it worked really well... is precipitation a zero-sum game?