If they didn&#x27;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.<p>What I&#x27;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 &quot;small&quot; 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&#x27;s fortunately a lot we <i>don&#x27;t</i> know about would be planet-busters, so let&#x27;s not find out any time soon....<p>As for melting lots of water, you&#x27;d probably be better off with the Antarctic ice pack, per Wikipedia it&#x27;s a order of magnitude larger, or 58 meters of ocean rising vs. a much more manageable 7.2.<p>Dumping soot on any of these would take a trick or three, since nuclear warheads are, if anything, I&#x27;m pretty sure way too energetic to directly do the chemistry, but I haven&#x27;t really thought about it yet.  You&#x27;d need to create soot upwind, which might be possible for Greenland, but wouldn&#x27;t it be a trick for either pole?<p>As for directly, if <a href="http:&#x2F;&#x2F;www.onlineconversion.com" rel="nofollow">http:&#x2F;&#x2F;www.onlineconversion.com</a> and my use of it is correct, 50 or even 100 Mt, perfectly applied to a cubic mile of ice, wouldn&#x27;t even come close to melting it, you&#x27;d need more than 334 Mt.  Mt -&gt; joules and cubic mile -&gt; 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.<p>Yeah, the Earth is big, and we&#x27;re pretty puny.  If only the bi-coastals who fly over fly-over country were inclined to do math when they looked down....