Why do the poles warm faster than the rest of the planet? [Alan]
For reasons related to the angle of incident solar radiation reaching their surface, the poles are colder than the rest of the planet (see Figure). The same shaft of light intensity is spread over a much wider range at the poles and thus is more diffuse – turning to heat and causing less cooling per m2. As a result, the poles support large masses of ice.
1) Considering the Arctic, because ice has high albedo (reflectance) much of the incoming solar radiation reflects back out into space. This means it does not reach an absorbent surface where it is transformed into heat. However, as warming occurs (whether due to atmospheric warming from above or, more likely, ocean warming from below), some of the ice melts. When it melts open water is exposed which does not reflect incoming radiation as effectively. Thus, a proportion of the radiation indeed turns into heat, warming the oceans further, and stimulating further ice-melt. The warming ocean, in turn, warms the atmosphere. Because the oceans become more and more exposed as ice reduces further, more and more heat is generated – causing regional warming.
Because the Antarctic is largely a land-based ice sheet there is no warm water below to cause melting – except under the ice shelves which are abundant and melting in west Antarctica.
2) Because the poles start colder, when air is warmed in tropical and temperature zones, and blown around – tending to equilibrate throughout the globe, those areas starting colder tend to warm up more.