I have not had much success finding out what the effects of bombarding a planet with comets or asteroids could have on the temperature of that planet.
I expect it would add some heat, and I understand it would be temporary. I understand that if it was a very large asteroid or a moon or something it could heat up the planet so much as to make it unlivable for millions of years. I guess I am more interested in the kinds of bombardments that could be done on a planet that already has inhabitants, at least living in enclosed habitats. I am sure there could be all sorts of effects depending on the composition of the object bombarding the planet, and the angle and location of bombardment. Maybe it could even kick up a bunch of dust or cause volcanic activity that would temporarily cool the planet?
I am mostly interested in the possibilities of adding heat to a planet via bombardment and I am wondering how much heat could be added compared to how devastating the impact would be and how long the heat would last. (Aside from the effects of whatever was in the comet being added to the atmosphere.)