Why Sea Level Rise May Be Faster than Forecast

50% acceleration of global sea level rise since 1993 pic.twitter.com/0SSgSvbssN

— Prof. Jason Box (@climate_ice) July 22, 2024

Leiria Economica:

According to a new study of the Greenland ice sheet, the climate model E3SM v.2 may do just that.overestimation of whitenessa basic property of ice. Which affects the speed of its dissolution. and thus rising ocean levels

Scientists need to make predictions about the future climate of our planet. Numerical representations of the Earth systemIn other words, models that are able to Accurately determines the albedo of different surfaces on our planet. To predict its tendency to heat or reflect solar radiation.

One common simplification used in most future climate models is to assume that Mountain glaciers and ice caps are associated with high albedo value.and above all constantIn fact, these surfaces are white in color and therefore must reflect a large portion of the light energy they receive.

However, the simplifications used in the modeling do not necessarily represent reality. In reality, at the edge of these large areas, the ice is often gray because it is bare (without snow) but also filled with darker holes, lakes in general, or even stained with algae and dust. Therefore, these sectors are quite wide depending on the area. Its albedo is much lower than the surrounding snow-covered ice, and therefore it warms up more quickly.

Based on this principle, researchers from the laboratory of Professor Charlie Zender at the University of California, Berkeley, have been interested in a model called E3SM (Energy Exascale Earth System Model). According to their results, the second version (v.2) of this model I overestimated the whiteness of the snow by about 5%

By recalculating this parameter using satellite data collected over the Greenland ice sheet, the study authors found that the new version of the E3SM model had He underestimated the melting of ice in this region by about 6 billion tons per year.compared to the older version of the same model.

This lower estimate corresponds to an additional loss of ice of about 145 billion tonnes between 2000 and 2021, equivalent to a 0.4 mm increase in sea level rise. 

This number may seem small at first glance compared to the 20 cm increase observed over the past century, but it is important to consider that this is only the difference related to Greenland’s albedo, So to underestimate this is to underestimate it is to underestimate it on a planetary scale!

CBS News:

Scientists have long thought that the glaciers in North Greenland have been stable — a vital condition, as they contain enough ice to raise the sea level by nearly 7 feet. But a new study published on Tuesday found that ice shelves in the region have lost more than a third of their volume in the last half-century because of rising temperatures — and if it continues, scientists say there could be “dramatic consequences” for glaciers, and the planet. 

Using thousands of satellite images and climate modeling, the study, published in Nature Communications, found that North Greenland’s ice shelves “have lost more than 35% of their total volume” since 1978. 

Ice shelves are the part of ice sheets — a form of glacier — that float over water. Three of those shelves in North Greenland have “completely” collapsed, researchers said, and of the five main shelves that remain, they said they have seen a “widespread increase” in how much mass they have lost, mostly due to the warming of the ocean. 

One of the shelves, called Steenbsy, shrank to just 34% of its previous area between 2000 and 2013. Along with the loss of overall ice shelf volume, scientists said the area of floating ice decreased by more than a third of its original extent since 1978. 

This observation could pose a major problem, as the Greenland ice sheet is the second-largest contributor to sea level rise. From 2006 to 2018, scientists noted that the single sheet was responsible for more than 17% of sea level rise in that period. 

“The observed increase in melting coincides with a distinct rise in ocean potential temperature, suggesting a strong oceanic control on ice shelves changes,” the study authors said. “…We are able to identify a widespread ongoing phase of weakening for the last remaining ice shelves of this sector.” 

Basal melting — the melting of ice from underneath — could also “be playing a complex and crucial role in thinning the ice shelf from below,” study’s authors said. And when that ice becomes too thin, it makes the structure more “prone to enhanced fracturing.”

“This makes them extremely vulnerable to unstable retreat and ice shelf collapse if ocean thermal forcing continues to rise, which is likely to be the case in the coming century,” they wrote, adding that the resulting discharge “could have dramatic consequences in terms of sea level rise.”