A new study published in the journal PNAS indicates that a section of the Greenland ice sheet has started to destabilize. The probability of crossing a point of no return and triggering a regional runaway of the cast iron is therefore more topical than ever. These results have major implications for sea level rise and slowing of ocean circulation in the North Atlantic.
Various theoretical assessments of ice cap stability indicate that the Greenlandic ice sheet is, in its current configuration, close to reaching a tipping point. In other words, it reached a level of warming from which the loss of mass of the cap accelerated sharply and irreversibly on the time scales that concern us.
When altitude variations lead the way
One of the main mechanisms of this runaway bears the name of melt-altitude feedback. It is structured as follows: when the temperature of the environment increases, the ice sheet melts and loses altitude, in particular on its margins. In doing so, the ice surface is deported to lower altitudes where the temperature is higher. The melting then accelerates accordingly, bringing the altitude of the ice sheet to an even lower level and exposing it to an even warmer environment, etc.
The process only stops when the ice sheet reaches a potentially very different configuration. in balance with new climatic conditions. The losses by melting and calving are then again balanced by the refreezing and the snow which precipitates on the cap. It goes without saying that with a much warmer climate, the equilibrium can be expressed in the total absence of an ice cap in Greenland. This is equivalent, we recall, to an elevation of around seven meters of sea level.
Greenland: evidence of the start of destabilization
However, data recently collected in the center-west of the ice sheet show that such a transition is currently taking place, at least on this part of the ice cap. A destabilization highlighted by the analysis of ice samples taken from the drainage basin of the Jakobshavn Isbræ glacier, one of the five largest in the ice sheet. With the help of numerical simulations, scientists were able to transcribe the rate of melting and regional altitude changes over the last 140 years. In other words, it dates back to 1880.
” We may be witnessing the start of a large-scale destabilization, but at the moment we cannot say, unfortunately. », Evokes Niklas Boers, main author of the paper. ” So far, the signals we are seeing are only regional, but this could simply be due to the paucity of precise and long-term data for other parts of the ice sheet. “.
Scientists explain that in the study area, the seesaw comes after a century of increasing melting. Indeed, the altitude of the ice is now so low thatit is no longer possible to stop the phenomenon, even by stabilizing the climate. The question now is to know to what extent these results are or are not representative of the stability of the rest of the ice sheet. ” We also need to keep a closer eye on other parts of the Greenland ice sheet, and we urgently need to better understand how different positive and negative feedbacks might balance out to get a better idea of how the ice sheet will evolve in the future. », Note N. Boers.