Australoid

Crisis! An asteroid 600m wide has been detected that's heading directly toward a major world population centre and is set to kill tens of millions. Your reaction? To yell "Bonza" and crack open a tin of the amber fluid. The governments of the world are ready to open their wallets to anyone who can save humanity, which means your decades of quixotic planning can finally turn into action in the capable hands of Aussie science.

After several years flat out like a lizard drinking, the Australian Space Agency finally gets the thermonuclear device into space and carefully positions it against the asteroid. The detonation minutely adjusts its course to send it from the east to hit the western end of the Great Australian Bight at an acute angle. The impact digs out a sub-sea-level crater 100 kilometres across and throws up a mountain range 1.5 km high, resulting in immediate hydration of the region and setting it up for continuing orographic precipitation. Ripper.

The rest of the world is relieved that disaster was averted but frankly they carry on like a bunch of Pommies about the years of atmospheric ash to follow.

There have been other ideas about an Australian Inland Sea, and ideas about saving the earth from rogue asteroids, but has there ever been a single idea that combines both into one and tosses in a mountain range for good measure? Beaut if I do say so myself.