At the end of summer 2021, it had rained for the first time on the glaciers in central Greenland. The event was then blamed for having caused a record retreat of snow and ice… But the data from the Sentinel-3A (Copernicus) satellite show that the thaw was already advanced because of the temperatures.
All these events remain complex to decipher.
Snow and… rain
The high altitude sites of the Greenlandic ice cap had so far been spared, only snow fell there. But, on August 14, 2021, the readings panicked, and scientists measured rain there for the first time, in quantity.
The following days, the melting is major, and many media make the link between this rain and the significant, almost fascinating, retreat of snow and ice on the white territory. 9 days later, the snow/ice limit has moved back, especially west of Greenland, by 50 kilometers! All that remains is the hard ice, the glacier, which is also melting rapidly. Near Kangerlussuaq, the cap had retreated almost 800 meters by the end of August. The link with heavy rain seems obvious at first glance. But that could be a misinterpretation.
The rain okay, but the heat, above all
Indeed, the study of data from the Sentinel-3A satellite, conducted by a team of Professor J. Box and published in the Geophysical Research Letters (international peer-reviewed journal), correlated with ground measurements, shows that the temperatures on the ice were very high in mid-August 2021. This was particularly the case over the western part of Greenland, while the ” normal seasonal at this time of year are generally more lenient.
The cycle was therefore already disturbed before the arrival of the rain, which had already generated pools of open water, torrents on the ice and a change in albedo (the “whiteness” of the ice cap) over the whole of the region as the fresh snow melted. The study concludes that even without the rain, still exceptional, the extreme heat for the month of August above the frozen continent would have generated massive melting.
And in the middle flows a river
More than the rain, we must therefore look for what led to these rains… However, it is a little more complicated than a simple heat wave. Scientists want to study a phenomenon that is currently poorly documented. These are the ” atmospheric rivers » (atmospheric rivers), capable of transporting water vapor hotter than the environment through which it passes, over very long distances. This may generate the type of melting observed last year.
Whatever the case, satellite measurements are, in this context, always more important for cross-referencing data with values at ground level or with atmospheric measurements. The European Union, which finances the Copernicus constellation program and its Sentinel satellites, has also planned to extend their capacities in the years to come.
Source :ESA
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