The earth's axis does shifts. The earth's axis shifts toward and away from the sun as it revolves around the sun. This movement of the axis is why we have the seasons every year. The top of the earth's axis or north pole is shifted away from the sun during the winter season in the northern hemisphere and then in the summer months of the northern hemispere the top of the axis or north pole is shifted toward the sun. This why it is hotter in the summer for the northern hemisphere and colder in the southern hemisphere.