Mine was to work tax policy to incentivize companies to make all their packaging shiny and white, incentivize people to litter, and disincentivize everybody from recycling.
My friend's was to use a giant rocket to push the earth farther away from the sun
Build a giant air conditioner in space and point it towards the Earth.
(Hey, it's just as plausible as expanding the orbit of the entire planet...)
Expanding the orbit of the Earth works under the known laws of physics but wouldn't be practically doable at all. A giant air conditioner wouldn't work for simple physics reasons.