It may be a silly question but why does the Arctic warm so fast despite being so white ("albedo" is the word, I believe)? Isn't all that whiteness supposed to deflect all those pesky sun rays back into space (or wherever)? I heard on BBC that they use white paint in India to paint rooftops so that it's not so scorching hot inside
The answers so far focus on feedback effects. But to my mind, those do not explain the phenomenon on their own, because there needs to be some warming signal to feed back, if you see what I mean.
I think there are a few first-order contributors, including:
- Ice is not a perfect reflector, so the sun warms the ice up a bit. Almost all reflectors absorb net radiation like this.
- The atmosphere is not perfectly transparent, so some of the reflected light is scattered and trapped in the atmosphere.
- The Arctic's climate is not a closed system, so for example it is subject to atmospheric conditions across the northern hemisphere and eventually the globe.
- The Arctic ice-cap floats entirely on the Arctic ocean, which is not a closed system either, so it is affected by the temperature of the world ocean. (And water has a large specific heat capacity, so it's a very effective carrier of heat. This is also why rain in Greenland is such a big issue.)
And for the reasons given by other respondents, all this is made much worse by the various positive feedback effects (which include more than just surface albedo; methane trapped in permafrost is a substantial problem).
So how is climate change and associated global heating driving Arctic amplification? This amplification is primarily caused by melting ice — a process that is increasing in the Arctic at a rate of 13% per decade.
Ice is more reflective and less absorbent of sunlight than land or the surface of an ocean. When ice melts, it typically reveals darker areas of land or sea, and this results in increased sunlight absorption and associated warming.
Polar amplification is much stronger in the Arctic than in Antarctica. This difference is because the Arctic is an ocean covered by sea ice, while Antarctica is an elevated continent covered in more permanent ice and snow.
The process is a positive feedback: Global warming, as a result of the anthropogenic enhancement of the atmospheric greenhouse effect, leads to loss of ice on planetary surfaces which decreases the planetary albedo (Earth becomes "less white"). This results in less solar radiation reflected back to space, and this further enhances global warming, thus accelerating ice melting, and so on.
While the Arctic may be 'whiter', it is also immensely sensitive.
Some context: during winter, there is an extended snow and ice cover; further, there is less incoming solar radiation during winter due to the axial tilt of the Earth.
During summer, snow melt, as well as young ice due to solar radiation increase (it is summer, right). Surfaces become brown, dark, in the tundra and rocky deserts.
Ice caps and glaciers are very thick, may loose mass and surface if their mass balance is negative which is usually the case presently. Also older ice (as in perennial or multi-year ice) is more compact and resistant to thawing than young ice, and thus count a lot for the albedo balance in the Arctic.
Then what happen is that climate changes are making perennial ice surface-area shrink: so once it is gone, it is gone. For example, the breakout of the Ward Hunt Ice Shelf (this is 83 degrees N):
An ice island about 1.5 kilometers long, 250 meters wide, and 30 meters thick moves into the Arctic ocean after the fracturing of the Ward Hunt Ice Shelf in August 2002.
And it is gone.
Of course the year after during winter a 1-2 m thick ice cover will form, and in July, will be thawed. So during August, September, the dark, black water of the sea will accumulate heat, warming since the albedo changed from whitish to dark, preventing an eventual restoration of the shelf in the short-to-medium term.
See this video (NASA) where the 1979-2020 shrink-expand cycle of the sea ice in the Arctic. Old ice is going away, and new ice is not living to the year after. More waves, stronger, during a longer interval since there is less cover means more energy and thus worse conditions for ice to reform.
Mid-latitudes to low-latitudes are also warming, but there is no loss of albedo equivalent to polar regions, explaining why the polar regions are sensible in comparison.