Due to global warming, Earth has become uninhabitable. The rich left off to colonize 'New Earth' while everyone else is left behind.
For whatever reason, the people left behind have survived, but out of sheer hatred have decided to go out to 'New Earth' and plunge it into an even worse but similar demise as the original Earth.
Their plan? To create a massive ship, fill it up with the solid form of a green-house gas and crash the ship into New Earth.
'New Earth' is a little smaller than earth and the surface is 90% water.
To define a 'successful' attack would to heat up the oceans enough to produce a large amount of steam. With steam also being a green-house gas, the planet would assumably begin to heat itself up and literally cook everyone on it.
What is the absolute best compound to use as the green-house compound to fill the crash ship and,
assuming distance isnt a problem, how large would this ship have to be?