The sun won't die for 5 billion years, so why do humans have only 1 billion years left on Earth?

" With a 10% increase of brightness from our star, the Earth will no longer be within the habitable zone. This will mark the beginning of the evaporation of our oceans. By the time the sun stops burning hydrogen in its core, Mars will be in the habitable zone, and the Earth will be much too hot to maintain water on its surface."