Simply painting roofs white in warm climates could decrease air conditioning bills for those buildings by 20%. That's one reason why California has required all new buildings to have white roofs for the past few years.
This new study says that if the 100 biggest cities painted all their roofs white, and switched their road materials to lighter colors (concrete instead of asphalt) it would reflect enough light and heat back into space to entirely offset the warming of the last few decades.
It's not a true fix for the problem, obviously, for that, we need clean, sustainable energy. But it could buy us enough time to make the changes we truly need.