I just read an
article estimating when the oceans will evaporate and no more free liquid water will be able to exist on the surface of the earth merely from the sun increasing luminosity over time (solar warming as opposed to global warming).
By astronomical observation the natural evolution of stars, like out own, indicates a slow increase in light output. Supposedly a little over a billion years from now our sun will be supplying 375 W/m^2 from the current 341 W/M^2 and that will produce enough evaporation to start uncontrolled global warming (the water itself becomes a greenhouse gas).