It is apparent that the Arctic is warming more than two times faster than the global average. This phenomenon – known as “Arctic amplification” – is causing drastic changes in the Arctic and has also been linked to extreme weather events in the mid-latitudes of the northern hemisphere.
The main cause of this is the changing “albedo” of the Arctic’s surface where the loss of snow and sea ice means less incoming sunlight is reflected back out to space.
The surface albedo feedback may account for 30% to 60% of the total Arctic warming. However, other processes trigger the surface albedo feedback role which are water vapor and confine Arctic warming to the surface by the absence of convection.
Convection happens when air close to the ground is heated by the warm surface of the Earth. The warmer air is lighter than the cold air above and so starts to rise. In the tropics, the ground – and the air directly above it – is always heated by the sun so there is a lot of convection and the atmosphere is “well mixed” with so much rising air.
At high latitudes, the angle between sunlight and the surface means the incoming sunlight is less concentrated at the surface. Because of this, the atmosphere is mostly heated by warm moist air coming from the tropics, which means there is much less vertical mixing.
The additional warming from the CO2 and other greenhouse gases that humans have emitted generally heats the atmosphere most near the Earth’s surface. In the presence of convection, this warming mixes vertically. However, at high latitudes – such as the Arctic – the absence of convection causes the warming from greenhouse gases to be larger close to the surface.
Another key reason for increased warming in the Arctic is the increase in transport of water vapour from the equator to the poles.
The warm moist air from the tropics gets transported to the poles by the circulation of the atmosphere, and keeps the difference in temperature between the poles and the equator relatively small.
As a warmer atmosphere can hold more moisture, it is expected that there will be more water vapour in the tropical atmosphere as global temperatures rise. This additional moisture is transported to the poles, where it condenses and releases heat.
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