Atmosphere And Weather

How the Reflective Index of Snow and Ice changes Global Temperatures



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On  planet earth, ice and snow, solid forms of water, exist as sea ice, lake and river ice, snow cover, glaciers, ice caps and frozen ground. Snow and ice have a major effect on global climate because they have a high reflective index. The reflective index of a medium is the ratio of the speed of light in vacuum relative to that in the considered medium. In simple words it gives an idea about the speed of light in that particular medium. So, the higher the refractive error, the lower the speed of light in that medium. When the reflective index is higher, a greater fraction of light is reflected back.

As mentioned earlier, snow and ice have a higher reflective index, which makes most of the sunlight which hits them reflect back in to space. If this did not happen, all the light rays that come from the sun would be absorbed in to the earth. These light rays do not contain only ‘light’. They also contain energy in the form of heat. Therefore, the rise in temperature is higher when more light is absorbed. Therefore, the increase in temperature of the surface of the earth is directly proportionate to the amount of ice and snow that is present.  

The reflective index of ice and snow can vary according to the surface roughness. Hong, Sungwook, Inchul Shin, 2010, have done a study named ‘Global Trends of Sea Ice: Small-Scale Roughness and Refractive Index’. The objective of the study was to analyze spatial and temporal characteristics of the average sea ice extent, surface roughness, and refractive index. They have used Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) for their study. According to them surface roughness is a major factor which affects microwave emission of the sea ice/snow surface. They have found out that the refractive error is increased in the summer, mainly due to melting of the ice. Therefore, during summer more light is reflected away into space. This phenomenon helps in keeping the Polar Regions cool and thereby helps in regulating the global climate.

According to the available data, there is a steady decline in Arctic sea ice due to increased air temperature, which is a result of air pollution. This has reduced the ability of the Polar Regions to regulate the world’s climate. Ultimately, all these series of events have resulted in a feed back loop which results in greater loss of sea ice.  


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