What if Earth had no natural satellites but the Sun was half as massive as it is in reality?

Consider this:<br><br>• The Sun is half as massive as it is in reality, so it emits half as much light and heat as it does now. In order for Earth to have liquid water, the reduced solar energy it receives must be somehow retained by the atmosphere.<br><br>• Earth has no natural satellites.<br><br>• The rest of the celestial mechanics of our solar system are the same as they are in reality.<br><br>What would be the effects on climate and the habitability of a planet like that?