If they didn't care about fallout, the Tsar Bomba would have had probably twice the yield, by substituting depleted uranium for the lead or whatever that was us

If they didn't care about fallout, the Tsar Bomba would have had probably twice the yield, by substituting depleted uranium for the lead or whatever that was used for the fusion tampers. What I've read is that, aside from bragging rights, and the occasional extremely hard target like Cheyenne Mountain Complex, somewhere slightly above 1 Mt you reach diminishing returns, because more and more of the energy released radiates out into space (note how "small" the normal size of nuclear warheads is nowadays, several hundred Kt times many and more accurately targeted warheads is generally the way to go). But there's fortunately a lot we don't know about would be planet-busters, so let's not find out any time soon.... As for melting lots of water, you'd probably be better off with the Antarctic ice pack, per Wikipedia it's a order of magnitude larger, or 58 meters of ocean rising vs. a much more manageable 7.2. Dumping soot on any of these would take a trick or three, since nuclear warheads are, if anything, I'm pretty sure way too energetic to directly do the chemistry, but I haven't really thought about it yet. You'd need to create soot upwind, which might be possible for Greenland, but wouldn't it be a trick for either pole? As for directly, if http://www.onlineconversion.com http://www.onlineconversion.com and my use of it is correct, 50 or even 100 Mt, perfectly applied to a cubic mile of ice, wouldn't even come close to melting it, you'd need more than 334 Mt. Mt -> joules and cubic mile -> cubic centimeters are astonishing close to equal, like within 0.4%, and 334 joules are required to convert a cubic centimeter at 0C to water at the same temperature, you got to love hydrogen bonding. Yeah, the Earth is big, and we're pretty puny. If only the bi-coastals who fly over fly-over country were inclined to do math when they looked down....