The sun won't die for 5 billion years, so why do humans have only 1 billion years left on Earth?
Apparently, the sun will be hot enough in a billion years to boil off the Earth's oceans. (And a few billion after that, it becomes a red giant that will expand out to the orbit of Mars.)
This reminds me, I was reading somewhere recently about how you could start moving the Earth's orbit outwards. (You swing a lot of things past it, if I recall correctly.) Can't remember where that article was, now.
I don't think it was this article from New Scientist in 2008, but it covers similar territory.