First, the obvious. Earth's climate will continue to change, as it always has, with or without mankind. What influences climate on Earth? It begins with the sun and its cyclical fluctuations, waxing and waning in strength over time. Our star is heating up with age, becoming 10% hotter every billion years. So we actually have roughly 250 million years left of planet habitability. Our orbit is elliptical and its course varies over time, altering the amount of solar heating we get. Our own magnetic field is weakening, having lost 6% in strength over the last 100 years. This allows more heating effect reaching Earth's surface. Also our axil tilt wobbles in cycles, allowing for changes in planetary heat distribution.