Ice - albedo feedback is the interaction between the cryosphere ( snow and ice-covered surface) and global climate. According to the terms of control theory, it is a "positive feedback ", which further enhances the efficient cause. Water and soil absorb about 90 % of the incident energy and heat up, leading to further melting of snow and ice. Conversely, cooling to an extent of snow and ice, thus to an increased reflection and further cooling.
Snow and ice have a high albedo ( reflectivity of sunlight ), only a small portion of the incident solar energy is absorbed. Snow-covered ice has an albedo of 0.9, the highest reflectivity. In contrast, the albedo of water is only about 0.06, that is, 94 % of the incident solar energy is absorbed, only 6% is reflected.
James Croll was the first scientist who recognized the importance of the ice - albedo feedback for the explanation of the origin of the ice ages.
The strength of the ice - albedo feedback can be seen, for example, the fact that in polar latitudes prevail low temperatures even in summer, although this time over 24 hours amount of energy received is greater than at the equator. In addition to the enthalpy of melting of the ice, this is the snow and ice due primarily to the strong albedo.
The phenomenon also has relevance in global warming: there amplifies the effect of greenhouse gases and is the main factor of the so-called polar amplification. First model calculations go to the Russian climatologist Mikhail Budyko in the 1960s back; already there, researchers had believed that a sea-ice decline in the Arctic would lead to a decrease in albedo.
As a result of global warming in the Arctic is an increasing glacier melt and the disappearance of Arctic ice is visible: are the basis of satellite measurements in the Arctic now (2014) data from 35 years ago; they show that the sea ice cover has declined there during the summer months by 40 percent.
In climate models, the influence of ice - albedo feedback is taken into account. A published study in 2011, however, indicates that all the models used for the published in 2007 IPCC report underestimated the effect; although the readings are certainly subject to error due to the relatively short observation period of only a normal period, the difference to the assumed in the climate models feedback is yet to be pronounced to be entirely attributed to measurement errors. According to the study, the average, additional radiative forcing, which was created in the last 30 years by reducing the ice - albedo feedback, at about 0.45 W / m² or 30% of the emitted since industrialization by man-made CO2 radiative forcing and This value is twice as high as in current climate models is assumed. The causes are unclear and not necessarily to be found in the global warming. This could be confirmed in another study, which was published in early 2014; based on satellite measurements, it was found that the Arctic ice - albedo has decreased strongly by a factor of two to three, can be expected to have than previous studies; distributed to the additionally recorded for this data energy evenly across the globe, they would correspond to 25 percent of the directly attributable to the increase of carbon dioxide in the atmosphere warming. This finding is not yet in the current climate development models.