Ice–albedo feedback is a positive feedback climate process where a change in the area of ice caps, glaciers, and sea ice alters the albedo and surface temperature of a planet. Ice is very reflective, therefore some of the solar energy is reflected back to space. Ice–albedo feedback plays an important role in global climate change. For instance at higher latitudes, we see warmer temperatures melt the ice sheets. However, if warm temperatures decrease the ice cover and the area is replaced by water or land the albedo would decrease. This increases the amount of solar energy absorbed, leading to more warming. The effect has mostly been discussed in terms of the recent trend of declining Arctic sea ice. The change in albedo acts to reinforce the initial alteration in ice area leading to more warming. Warming tends to decrease ice cover and hence decrease the albedo, increasing the amount of solar energy absorbed and leading to more warming. In the geologically recent past, the ice-albedo positive feedback has played a major role in the advances and retreats of the Pleistocene ice sheets. Inversely, cooler temperatures increase ice, which increases albedo, leading to more cooling.
Evidence
Snow and ice-albedo feedback tend to amplify regional warming due to anthropogenic climate change. Due to this amplification the cryosphere is sometimes called the "natural thermometer" of Earth because changes in each of its components have long lasting effects on the systems of Earth. Internal feedback processes may also potentially occur. As land ice melts and causes eustatic sea level rise, it can also potentially induce earthquakes as a result of post-glacial rebound, which further disrupts glaciers and ice shelves. If sea-ice retreats in the Arctic, the albedo of the sea will be darker which means more warming. Similarly, if the Greenland or Antarctic land ice retreats, the darker underlying land is exposed and more solar radiation is absorbed.
The runaway ice-albedo feedback was also important for the Snowball Earth. Geological evidence show glaciers near the equator, and models have suggested the ice-albedo feedback played a role. As more ice formed, more of the incoming solar radiation was reflected back into space, causing temperatures on Earth to drop. Whether, the Earth was a complete solid snowball, or a slush ball with a thin equatorial band of water still remains debated, but the ice-albedo feedback mechanism remains important for both cases.
Ice-albedo feedback on exoplanets
On Earth, our climate is heavily influenced by interactions with solar radiation and feedback processes. One might expect exoplanets around other stars to also experience feedback processes caused by stellar radiation that affect the climate of the world. In modeling the climates of other planets, studies have shown that the ice-albedo feedback is much stronger on terrestrial planets that are orbiting stars that have a high near-ultraviolet radiation.
