If Earth ever suffers a runaway greenhouse effect (like what has happened on Venus), then our atmosphere would trap excess amounts of solar energy, the air temperature would rise, and the oceans would swiftly evaporate into the atmosphere as they sustained a rolling boil. This would be bad.
I want to create the airplane that flies in the rarified atmosphere of Mars. This is what galvanizes a generation to want to become scientists and engineers in the first place, not we need a scientist to develop a plane that's 20 percent more fuel-efficient than the one your parents flew.