While the Greenlandic INLANDESIS has warmed almost 3 ° C since 1982, its Albédo has decreased continuously. Thus, ice reflects less effectively solar radiation, which increases the speed of its decline all the more. Recent works combine this damage to an apparently anecdotal property: the shape of the snowflakes placed on the cap.
L’albédo From a surface designates the ratio between the quantity of light that arrives on this surface and the thoughtful fraction. The higher it is (close to 1), the greater the thoughtful radiation. On the contrary, an albedo close to 0 indicates that energy is essentially absorbed by the surface. For these reasons, we are also talking about
powerful power.
At the origin of a decline albedo
Composed of ice and snow, the Greenland ice cap naturally has a very high albedo. In fact, an important fraction of incidental solar energy is returned to space, perpetuating the cold conditions that maintain the INLANDSIS in place. However, with climate change, we observe a generalized darkening of the ice surface.
Although still high, the Albédo declines, testifying togreater absorption of solar radiation in summer. Result: the cast iron accelerates, which makes the surface still a little darker and decreases the albedo of the cap all the more. It is a real vicious circle. However, if satellite observations have demonstrated the existence of darkening, the question of its precise engine has so far been unresolved.
In a new study, researchers discovered that some parts of Greenland had become
Less exposed to snowfall. However, as fresh snow has an extremely high reflective power, this means that these areas darken. “” As snow ages, even in a few hours to a few days, you get this reduction in reflectivity, which is why fresh snow is so important », Note Erich Osterberg, paper co -author.
Trend in the Albédo (A), the size of the snow grains (B), the temperature (C) and the incident solar radiation (d) between 1996 and 2017. Only summer months (JJA) come into account. Finally, the black brands locate the course on which the samples have been taken and the measures made. Credits: Gabriel
Lewis et coll. 2021.
The granulometry of snow, a detail with the main consequences
Scientists note that the reduction in precipitation is explained by an increase in anticyclonic blockages in the region since the mid -1990s. The disturbed rail then circulates too much to the north or too much to the south to really concern Greenland. In addition, these high pressure bubbles are accompanied by a clear sky, therefore of high sunshine and an abnormally soft air mass at altitude.
« It’s like a triple pain », avance Erich Osterberg. « All this contributes to an increasingly rapid melting of Greenland ». And it is not necessary to modify the Albédo many so that the repercussions are significant. Indeed, A decrease of only 1 % would be enough to destock 25 billion additional tonnes of ice over three years. But why does white gold recently fallen has a reflective power so different from that dated just a few days?
« Fresh snow looks like what you would draw in a kindergarten class or cut into a piece of paper. She has all these really sharp points because it is extremely cold in the atmosphere when the snow falls “, Details Gabriel Lewis, principal author. “” Once it falls and rests on the surface of the ice cap in the sun, it changes shape and the grains of snow become larger over time ».
According to data on-sitethe decrease in the Greenlandic albedo would therefore be essentially due to A change in the texture of the snow. We are talking about increased grain size, the flakes becoming larger and rounded. Finally, observations also show that a possible increase in dust in the ice cannot be questioned. “” In our field of research, impurities do not seem to be sufficient to explain the change of Albédo that other research teams have reported “Reports the co -author.
The change in shape of snowflakes, caused by hot and sunny conditions, also plays a key role in the drop in the Albédo du Greenland. Indeed, when the flakes fall, their structure is complex and has many lively edges, which allow an effective reflection of solar radiation. However, once on the ground, these flakes undergo a rapid transformation under the effect of the sun and the temperature, their grains become more rounded and grow, thus reducing their reflective capacity. This process, called metamorphosis of snow, contributes significantly to the decline of the albedo of the glacial cap and therefore to the acceleration of the cast iron.
