On a global scale, average temperatures of 2005 to 2009 were higher by about 0:54 C, compared tothe average of 1954 to 19801.
However, Arctic temperatures increased by 2 C to 4 C over the sametime period. In a recent paper Johannessen et al. (2016) showed that the strongest increase of up to3 C occurred during winter time in the recent years compared the temperature of the Northern Hemisphere(NH) with now significant amplification during summer time compared to the NH. Severalgeophysical aspects, which are unique to the high latitudes, cause this effect, called the Polar or ArcticAmplification.
Arctic amplification can be seen as one of the main triggers of changing the MIZ,so understanding this process is crucial to grasp why the MIZ is so unpredictable and fast-changingzone.To understand Arctic amplification, we need to start with the realization that the incoming solarradiation is either absorbed or reflected by different terrestrial or marine bodies, such as sea ice. Theability of a body to reflect incoming solar radiation (light) is called albedo. Hence, the “whiter” anobject is and/or the smaller the angle of the object to the light source (sun) is, the higher is the albedoor the objects reflectiveness.
Due to the Earth’s spherical shape, the Polar Regions have a much higheralbedo and a larger area per incoming radiation, compared to the lower latitudes. These factors are theessential precondition for the permanent formation, and accumulation, of ice and snow in these areas.Compared to “blue” oceans and “green” land, ice and snow have a much higher albedo, meaning thatthe cryosphere is absorbing much less energy than the other systems. Increased solar intensity (e.
g.by more atmospheric CO2) may result in increased melting of ice and snow. If, for example, the seaice is melting, the area of energy-absorbing water is increasing, while the albedo is decreasing, a socalled a positive (self-enhancing) feedback; less sea ice resulting in increased melting.
This processwas coined Polar amplification, as temperature changes in the high Polar regions are amplified duringfall, winter and spring (Johannessen et al., 2016) due to this positive feedback.In addition, sea ice is acting as a lid, insulating the atmosphere from higher oceanic temperatures.This lid is effectively reducing the heat flow between the ocean and the atmosphere by about twoorders of magnitude. This effect is of great importance for the latent and perceptible exchange ofwarmth between the ocean and the atmosphere, which controls the high variability of the MIZ to alarge extend.1meereispor
