When you talk about destructive power so casually,You are not even considering the most destructive of them all Nuclear fallout.a Castle Bravo surface burst of a 15 Mt thermonuclear device at Bikini Atoll had a fallout area extending over 500 km downwind.Majority of this fallout region was severely contaminated,some Japenese fishermen happen pass through these area got exposed, and one of them died causing an international furore.The Castle Bravo fallout spread traces of radioactive material as far as Australia, India and Japan, and even the United States and parts of Europe. Though organized as a secret test, Castle Bravo quickly became an international incident, prompting calls for a ban on the atmospheric testing of thermonuclear devices.Now there is no way I can predict the fallout area of a 1 GT bomb,but it will be pretty bad.
I mean even Soviets got scared of building a 100 MT bomb, and they were reportedly terrified after the Tsar Bomba test.It has been estimated that detonating the original 100 Mt design would have released fallout amounting to about 25 percent of all fallout emitted since the invention of nuclear weapons.Hence, the Tsar Bomba was an impractically powerful weapon.