At these time scales, major terraforming projects become viable, from building large sunshades in orbit to one near Earth-Sun L1 (balancing light pressure and gravity, it would be closer to the Sun than L1), to even raising Earth’s orbit through a fleet of gravity tugs. Venus would be an excellent case for a planet-sized sunshade, btw, as well as a solar wind magnetic lens to replace lost hydrogen and make liquid water as the planet cools. The latter could be useful for Mars.