ICE CLOUD FEEDBACK PROCESS
Because of the impact of clouds on the surface radiation flux and thus the state of the sea-ice surface, cloud radiation feedback processes in the Arctic are inextricably linked with albedo feedback processes. A perturbation in the surface radiation balance of the snow or ice, which could be produced by input of greenhouse gases and aerosols, results in a change in snow or ice characteristics. These changes in surface characteristics, particularly the surface temperature and fraction of open water, will modify fluxes of radiation and surface sensible and latent heat, which will modify the atmospheric temperature, humidity, and dynamics. Modifications to the atmospheric thermodynamic and dynamic structure will modify cloud properties, which will in turn modify the radiative fluxes.
ICE ALBEDO FEEDBACK
Ice-albedo feedback (or snow-albedo feedback) is a positive feedback climate process where a change in the area of snow-covered land, ice caps, glaciers or sea ice alters the albedo. This change in albedo acts to reinforce the initial alteration in ice area. Cooling tends to increase ice cover and hence the albedo, reducing the amount of solar energy absorbed and leading to more cooling. Conversely, warming tends to decrease ice cover and hence the albedo, increasing the amount of solar energy absorbed, leading to more warming.
The effect also applies on the small scale to snow-covered surfaces. A small amount of snow melt exposes darker ground which absorbs more radiation, leading to more snowmelt.
The effect has mostly been discussed in terms of the recent trend of declining Arctic sea ice. Internal feedback processes may also potentially occur, as land ice melts and causes eustatic sea level rise, and also potentially induces earthquakes as a result of isostatic rebound, which further acts to disrupt glaciers, ice shelves, etc.
ICE INSULATING FEEDBACK
Sea-ice helps to keep the Artic cold.
During winter, the Arctic’s atmosphere is very cold. In comparison, the ocean is much warmer. The sea ice cover separates the two, preventing heat in the ocean from warming the overlying atmosphere. This insulating effect is another way that sea ice helps to keep the Arctic cold. But heat can escape rather efficiently from areas of thin ice and especially from leads and polynyas, small openings in the ice cover. Roughly half of the total exchange of heat between the Arctic Ocean and the atmosphere occurs through openings in the ice. With more leads and polynyas, or thinner ice, the sea ice cannot efficiently insulate the ocean from the atmosphere. The Arctic atmosphere then warms, which, in turn influences the global circulation of the atmosphere.
In summer the reflection of sunlight by sea ice prevents the ocean below the ice from absorbing solar energy, keeping the ocean cooler.
Its high reflectivity and low thermal conductivity, along with the high amounts of latent heat required to convert ice to liquid water make sea ice an important player in defining the unique local character of the Arctic climate. Sea ice effectively insulates the atmosphere from the underlying warm ocean water. In comparison to the open ocean, for instance, sea ice surfaces moderate surface heat and moisture fluxes, equilibrate relatively quickly, and especially during winter quickly cool and dry the overlying atmosphere. The most direct consequence of ice cover change, is the impact on surface energy fluxes that change the thermal regimes of the local atmosphere.
The change in ice cover changes the insulation : a positive feedback
MERIDIONAL OVERTURNING CIRCULATION AND SEA ICE SURFACE TEMPERATURE FEEDBACK
while the actual future path of the Atlantic meridional overturning circulation(MOC) is not known, it is possible that in the short term the ocean could act as a negative feedback to high-latitude warming. The role of deep ocean heat in the antarctic subpolar gyres (delivered by the MOC) plays a critical role in regulating the thickness of the insulating Antarctic sea-ice cover. Consequently, one may assue heat content and thus the sea-ice thickness. The latter will impact the length of the sea-ice season, insulating effectiveness, freshwater transport by sea-ice drift, and deep and intermediate water formation (feeding back into the MOC directly). It is difficult to predict the nature of the sign of the net feedback, since we need a better understanding of how changes in the MOC may impact the properties of the subpolar deepwaters.
The net change will depend upon the balance of a variety of detailed local air-sea-ice exchange processes, and this is difficult to estimate in typical low-resolution climate models.
