The Arctic acts as a thermostat for the global climate.
We can expect to see Arctic change have global environmental and socioeconomic consequences. ( Don Perovich, Dartmouth University expert on sea ice 2012)
The science is covered in some detail by earth. Arctic sea ice fluctuations pose significant impact on local climates. Changes in sea ice cover alter surface heat and radiation fluxes, surface and atmospheric temperatures, precipitation characteristics, storm tracks, cyclonic activity, as well as local and synoptic scale atmospheric circulation. These modifications are known today to propagate to the lower latitudes with potentially significant consequences for global climates.
There are in fact several contributions to the sea ice melt positive feedback, that results in more warming,
- Loss of snow and sea ice reflectivity of solar energy (ice albedo feedback)
- both thinning and loss of extent reduces sea ice albedo.
- Thin sea ice also lets more solar energy through the ice warming it from inside
- Heat energy absorption by exposed dark open water and land surface
- Loss if sea ice insulation of water.
- Latent heat of ice
The feedback increases the Arctic regional warming, Northern hemisphere warming and lastly to some degree global warming.
The whole feedback process is also self accelerating, because more local Arctic warming directly melts more ice and snow.
Latent heat of ice
This is a big factor though it is still not taken on board by many environmental scientists. The point about summer conditions is that as long as there is SOME ice present on the sea surface, however thin the layer, then the ocean temperature below it is held to 0 degrees C because the absorbed solar radiation melts the bottom of the ice rather than warming the water. Also the atmospheric temperature is held to close to 0C because warmer air melts the surface snow layer on top of the ice and is thereby cooled. The sea ice, even when thinned, continues to act with 100% efficiency as an air conditioning system for ocean and atmosphere alike. BUT, as soon as the sea ice layer goes, this process ceases and the sea can warm up rapidly (to typically 7C by the end of summer - which is not much colder than the North Sea), as can the atmosphere (which speeds up Greenland ice sheet melt when that warmed air passes over Greenland). Latent heat is an enormously powerful buffer - the amount of heat that you have to pump in to melt 1Kg of ice will subsequently heat that same amount of melted water to 80C.
So once the ice goes away entirely there is a big jump in temperatures in the upper ocean and atmosphere (with dire consequences for permafrost), and it is very difficult to see how one can ever go back to an ice-covered summer ocean once this has happened. (Prof Peter Wadhams personal communication).