Ice melting because of global warming: What is it? Where is she going ?
Acting as insulation between the ocean and atmosphere, changing the salinity and thus the underlying water density, the ice is an important part of ocean circulation and as a result of climate warming.
Formation of the ice
The inclination of 23 ° to the axis of the earth on the plane of its orbit prevents the sun from reaching the 2 poles simultaneously. The lack of sun on a pole plunges it into the night for months 6 On land falling snow turns to ice forming ice caps.
Meanwhile under the action of intense cold ocean surface temperature decreases slowly. As sea water contains salt - of 29 35 in grams per kilogram of water in polaires- regions, it will not freeze to 0 ° C such as fresh water but at a temperature between -1,7 ° -1,9 C and ° C. When approaching these temperatures ice crystals are formed and it was then that the ice appears.
The ice acts as an insulating layer between the ocean and atmosphere by reflecting about 70% of the solar energy that reaches the surface. Area covered by snow and ice therefore absorbs 30% of this energy while a free sea absorbs almost 95%. This process limits the cast and the maintenance of the ice for several months.
Roles in the climate balance
Training ice rejects the very salty waters, cold and dense, which in some ocean regions will plunge to the bottom of the ocean (especially around the Antarctic continent). On the surface, for compensation, warmer waters tributary. We call these combined oceanic transport of heat and salt: thermohaline circulation.
As a solid surface, the ice cut of the rainfall, which accumulate on the surface instead of joining directly the ocean. Furthermore, as the sea ice is much less saline than seawater, any creation or ice melt automatically leads to a change in the salinity of the ocean surface at this location.
Constantly moving, driven in particular by ocean currents and wind, the ice creates significant transport fresh water and salt, which in turn act on global ocean circulation and thus on the global climate.
The future of the sea ice
Météo-France has a coupled ocean-ice-atmosphere that allows, for example to assess the impact of an increase in the concentration of greenhouse gases and atmospheric aerosols on the climate of the planet and the ice.
Various simulations based on a doubling scenario of atmospheric carbon dioxide by 2100, translated the impact of this evolution:
· A totally disappearing Arctic sea ice in summer by the end of the XXI century. In winter, the ice would be much thinner than at present (a few tens of cm instead of 2m about), but almost as wide.
· An Antarctic ice a little less extensive than at present
It is estimated, according to the observations, the average thickness of Arctic sea ice fell from 3 1,80 m m 1980 to today. Is this change due to global warming due to human activities? Is it a natural phenomenon? It is currently too early to answer this question.
Today, coupled models are sophisticated enough to properly simulate the characteristics of the global climate system and produce reliable results. The latter, which go in the same direction as those of other research institutes, are refined continuously by model advances the Earth's climate system.
But already, a proper consideration of sea ice in the studies on climate change is needed.