At night the temperature drops not due to a lack of CO2, but due to a lack of sunlight. If we were to be able to partially block the sun, or reflect significantly more sunlight back into space, we would indeed be able to lose heat more more quickly, but that would require engineering on a scale we've never done before.
So sure, paint the entire Earth white, but how? Or build a giant solar screen in space, but again: how? Besides, blocking sunlight will also have many negative repercussions.