... by relying on the greenhouse effect from carbon dioxide. And you wouldn't want to do that, anyway, since it would result in a carbon dioxide concentration

... by relying on the greenhouse effect from carbon dioxide. And you wouldn't want to do that, anyway, since it would result in a carbon dioxide concentration too high for an eventually breathable atmosphere. What you really want there is water vapor and perfluorocarbons. But cranking those out takes time. Mars might be warm in 1000 years. Still, shorter than the trip to another star.