Positive and negative feedbacks in glacial periods

This low precipitation allows high-latitude snowfalls to melt during the summer. An ice-free Arctic Oceanand more southerly latitudes, reducing the temperatures over land by increased albedo as noted above. Furthermore, under this hypothesis the lack of oceanic pack ice allows increased exchange of waters between the Arctic and the North Atlantic Oceans, warming the Arctic and cooling the North Atlantic. (Current projected consequences of include a largely ice-free Arctic Ocean within 5–20 years, see Additional fresh water flowing into the North Atlantic during a warming cycle may also reduce the (see Such a reduction (by reducing the effects of the would have a cooling effect on northern Europe, which in turn would lead to increased low-latitude snow retention during the summer absorbs solar radiation during the long summer days, and evaporates more water into the Arctic atmosphere. With higher precipitation, portions of this snow may not melt during the summer and so glacial ice can form at lower altitudes

Ice and snow increase the Earth's i.e. they make it reflect more of the sun's energy and absorb less. Hence, when the air temperature decreases, ice and snow fields grow, and this continues until competition with a negative feedback mechanism forces the system to an equilibrium. Also, the reduction in caused by the ice's expansion increases albedo.