Ice–albedo feedback

Ice–albedo feedback is a climate change feedback, where a change in the area of ice caps, glaciers, and sea ice alters the albedo and surface temperature of a planet. Because ice is very reflective, it reflects far more solar energy back to space than open water or any other land cover. It occurs on Earth, and can also occur on exoplanets.

Since higher latitudes have the coolest temperatures, they are the most likely to have perennial snow cover, widespread glaciers and ice caps - up to and including the potential to form ice sheets. However, if the warming occurs, then higher temperatures would decrease ice-covered area, and expose more open water or land. The albedo decreases, and so more solar energy absorbed, leading to more warming and greater loss of the reflective parts of the cryosphere. Inversely, cooler temperatures increase ice cover, which increases albedo and results in greater cooling, which makes further ice formation more likely.

Thus, ice–albedo feedback plays a powerful role in global climate change. It was important both for the beginning of Snowball Earth conditions nearly 720 million years ago and for their end about 630 mya: the deglaciation had likely involved gradual darkening of albedo due to build-up of dust. In more geologically recent past, this feedback was a core factor in ice sheet advances and retreats during the Pleistocene period (~2.6 Ma to ~10 ka ago). More recently, human-caused increases in greenhouse gas emissions have had many impacts across the globe, and Arctic sea ice decline had been one of the most visible. As the sea ice cover shrinks and reflects less sunlight, the Arctic warms up to four times faster than the global average. Globally, the decades-long ice loss in the Arctic and the more recent decline of sea ice in Antarctica have had the same warming impact between 1992 and 2018 as 10% of all the greenhouse gases emitted over the same period.

Ice–albedo feedback has been present in some of the earliest climate models, so they have been simulating these observed impacts for decades. Consequently, their projections of future warming also include future losses of sea ice alongside the other drivers of climate change. It is estimated that persistent loss during the Arctic summer, when the Sun shines most intensely and lack of reflective surface has the greatest impacts, would produce global warming of around 0.19 °C (0.34 °F). There are also model estimates of warming impact from the loss of both mountain glaciers and the ice sheets in Greenland and Antarctica. However, warming from their loss is generally smaller than from the declining sea ice, and it would also take a very long time to be seen in full.