USA vs Europe
I know that in the USA warning shots are not very popular to say the least. We had a thread here some months ago which got pretty hot...
aaanyway: We in Austria/Europe do shoot warning shots with quite some success. Austrian police ammo (Fiocchi/Hirtenberger FL, 9x19mm, Glock 17) doesn't ricochet at all if fired straight into the floor (Street, concrete etc) at angles below 15°.
Don't fire warning shots into the air, the bullets come down almost as fast as they went up and can easily kill somebody miles away. Just DONT.
Fire warning shots straight down as straight as you can and WATCH YOUR FEET! You could also choose a secure backstop such as a concrete wall more than 10yds away or sand etc. Warning shots are much better than having to shoot somebody. So if there's time for it and a secure backstop it's a very smart alternative to killing. The sobering effect of a warning shot can be immense. However, only fire a warning shot if you have enough time to fire COM in case the BG doesn't react to your warning shot.
This is not about being allowed to shoot at somebody or not. This is about achieving control of a dangerous situation without having to kill a human, dog or whatever. If you have an alternative - use it for your own sake. Even if you were right and defending innocent life, you'd still have to cope with having killed somebody. And that's not an easy thing anyway...
Si vis pacem - para bellum
If you want peace - prepare for war