What do the outfit you wear when walking in the desert have in common with the snowy “coat” worn by ice? The answer: whiteness. The amount of solar radiation reflected from a surface depends on its physical properties, especially its color. Whether you are a Bedouin… or from a very hot planet, it is better to wear white.
However, to make predictions about the future climate of our planet, scientists need numerical representations of the Earth system. In other words, models. The simplification is that frozen surfaces, especially mountain glaciers and ice caps, are associated with a high and constant albedo value. After all, aren’t they white?
In fact, at the edges of these areas, the ice is often grey because it is bare, that is, devoid of snow. But it is also dotted with darker “holes” that correspond to lakes. Even stained with algae and dust. These dark frozen areas reflect less solar radiation: they are less albedo, and heat up more.
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Six billion tons of additional cast iron per year
Chloe Clarke, a researcher in Professor Charlie Zender's lab atUniversity of California, Irvinewas interested in a model called the E3SM (Earth System Exascale Energy Model). According to his team's findings published in the journal Journal of Geophysical Research: Atmospheres (April 2024) The second version (version 2) of the model overestimated the snow albedo by about 5%.
By recalculating this parameter using satellite data collected over the Greenland ice sheet, the researchers found that ice melt in this region was occurring at a rate of about six billion additional tons (6 gigatons) per year, compared to what was estimated in the old version of the model.
Between 2000 and 2021, this coincided with an additional 145 billion tons of ice loss, equivalent to an increase in sea level rise of 0.4 mm.
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This is not much, of course, compared to the average rise in ocean levels measured over the past century of more than 20 centimeters (our-environment.gouv.fr). But that's just the difference in Greenland's albedo. The US team plans to study other frozen surfaces on the planet, such as glaciers in the Andes and Alaska, for a global assessment.
Vicious circle and virtuous circle
Beyond the numbers, the study above all highlights the fact that small-scale physical features can have dramatic consequences for the global climate.
“I think our work will help models better understand climate feedbacks,” (Positive or negative loop effects, editor's note) related to snow and ice“In fact, climate change leads to a vicious cycle: when ice melts, the surface albedo decreases, temperatures increase, more ice melts, and so on,” the lead author hopes (press release).
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Last month, a study by Aarhus University in Denmark confirmed that giant viruses discovered in the Greenland ice sheet could limit melting by regulating the blooming of algae that deform the snow in spring. It’s a virtuous circle this time around, one that doesn’t exempt humanity from drastically cutting greenhouse gas emissions.
