Another way to increase the temperature could be to direct small cosmic bodies (asteroids) onto the Martian surface; the impact energy would be released as heat and could vaporize Martian water ice to steam, which is also a greenhouse gas.
Another way to increase the temperature could be to direct small asteroids onto the Martian surface; the impact energy would be released as heat. This heat could sublimate or, if there is liquid water present at this stage of the terraforming proccess, could vaporize it to steam, which is also a greenhouse gas.