Extreme weathering refers to weathering which are too extreme to be natural. A notable movie which tells of this is "The Day After Tommorow" in which due to man-kind's pollution, the weather becomes extreme and causes a new Ice Age.
This mainly refers to two different consequences - a new Ice Age or the Earth will become too hot for man-kind to survive in and thus causing evolution or total annihilation.
A New Ice Age?
There have been many significiant hints of which caused scientists to think that there night be a new Ice Age coming.
Heat waves are long periods of abnormal high temperatures, which can cause droughts. If the period of heat waves are long enough and the area of the affect is wide enough, it is possible to cause the extinction of many organisms on Earth.