I don't have proof, but consider this:
From space (say a geo-stationary satellite) you could see the curvature of the earth, right?
Now at the same location but on the surface of the earth you assume it is completely impossible to view the curvature of the earth. This implies that if you would travel from your location on earth to the satellite, at some point a change occurs that allows you to suddenly see the curvature.
Can you describe at what altitude this would be? I contend that at diminishing altitudes (not considering obstacles) the curvature is less obvious, but will never actually reach zero. Therefore, given good eyesight it should be possible to see the curvature of the earth.
I like thought experiments such as this, I'm not always good at describing my thoughts though, so if I'm rambling please say so
