Orbital forcing is the effect on climate of slow changes in the tilt of the Earth's axis and shape of the orbit (see Milankovitch cycles). These orbital changes change the total amount of sunlight reaching the Earth by up to 25% at mid-latitudes (from 400 to 500 Wm-2 at latitudes of 60 degrees). In this context, the term "forcing" signifies a physical process that affects the Earth's climate.