text: When the melted area reveals surfaces with lower albedo, such as grass, soil, or ocean, the effect is reversed: the darkening surface lowers albedo, increasing local temperatures, which induces more melting and thus reducing the albedo further, resulting in still more heating.Snow Snow albedo is highly variable, ranging from as high as 0.9 for freshly fallen snow, to about 0.4 for melting snow, and as low as 0.2 for dirty snow.Over Antarctica snow albedo averages a little more than 0.8.If a marginally snow-covered area warms, snow tends to melt, lowering the albedo, and hence leading to more snowmelt because more radiation is being absorbed by the snowpack (the ice–albedo positive feedback).Just as fresh snow has a higher albedo than does dirty snow, the albedo of snow-covered sea ice is far higher than that of sea water.Sea water absorbs more solar radiation than would the same surface covered with reflective snow.When sea ice melts, either due to a rise in sea temperature or in response to increased solar radiation from above, the snow-covered surface is reduced, and more surface of sea water is exposed, so the rate of energy absorption increases.The extra absorbed energy heats the sea water, which in turn increases the rate at which sea ice melts.As with the preceding example of snowmelt, the process of melting of sea ice is thus another example of a positive feedback.Both positive feedback loops have long been recognized as important for global warming.Cryoconite, powdery windblown dust containing soot, sometimes reduces albedo on glaciers and ice sheets.The dynamical nature of albedo in response to positive feedback, together with the effects of small errors in the measurement of albedo, can lead to large errors in energy estimates.