One of the most worrying predictions about climate change may well be a reality

Two years ago, NASA's former climatologist, James Hansen and several colleagues, set a dramatic scenario in which gigantic waves of cold water from melting glaciers could increase the flow of the oceans, leading to a faster increase in the level of the oceans around the world, as well as the formation of very large storms.

You have to know that Hansen's scenario was based on a computer simulation and not on real world real data. As a result, his suggestion met with skepticism from a number of other scientists around the world. However, now, a new oceanographic study seems to confirm one aspect of this picture, at least in the beginning.

The new research, based on ocean measurements off the coast of East Antarctica, shows that the melting of Antarctic glaciers actually refreshes the surrounding ocean. Then this, in turn, blocks a process in which cold, salty water flows below the surface of the sea in winter, forming " the densest water on Earth ", in the words of the main author of the 'study, Alessandro Silvano, researcher at the University of Tasmania in Hobart.

Indeed, research shows that this Antarctic groundwater has ceased to form in two key areas of Antarctica: the west coast of Antarctica and the east coast around Totten Glacier. These are the two regions where ice melts fastest in Antarctica, and it is not surprising that cold surface water no longer flows in the depths, and only a layer of warmer water. the ocean can freely travel across the continental shelf and reach the bases of the glaciers, retaining its warmth (as the glaciers stay above).

This warmer water then melts glaciers and large floating ice platforms. In other words, the melting of the Antarctic glaciers seems to cause a sort of "loop" of melt, which can not be stopped. The ice initially melted in fresh water is trapped on the surface, while the warmer water stays below. Then, this bottom layer melts glaciers and creates more meltwater - not to mention the rising waters when glaciers lose mass. " What we discovered is not just from a modeling study, but it's something we've seen in the real ocean ," said Silvano, who led the research with colleagues several other institutions in Australia and Japan. " Our study shows for the first time concrete evidence of this mechanism. It demonstrates that these processes are already underway, "added Silvano.

Hansen said, " This study provides a fine, small-scale example of the processes we are discussing in our paper ." " As for the larger issue, it is still too early to say how these actions will unfold. If we stay on the usual emissions [greenhouse gases], and therefore global warming continues to increase, I expect the rate of freshwater injection to increase. This will be played out over the next few years and decades, "continued Hansen.

A photo of icebergs in Antarctica, in December 2016. Credits: Alessandro Silvano

According to Matthew Long, an oceanographer with the National Center for Atmospheric Research, the study is " consistent with much of the existing research that demonstrates the warming and cooling of the deep ocean in the southern hemisphere ." " The fact that we are seeing constant warming and cooling of the water because of the melted ice indicates that the processes are already under way. Indeed, this study is part of a growing body of evidence suggesting that the world's oceans are changing - and this pace of change is starting to accelerate, "said Long.

If the process of Antarctic groundwater formation is altered, at least in some areas, this would be a southern hemisphere analogue of a process that has already caused great concern and attracted much more attention: the potential slowdown in North Atlantic traffic caused by melting ice in Greenland.

" Of these two key areas of deep-sea formation, the North Atlantic has been considered more vulnerable globally to global warming ," said researcher Stefan Rahmstorf. Potsdam Institute for Climate Research. The latter also claims to have discovered changes in deep-water formation in the North Atlantic: "So it is a source of concern that we now see similar signs in the Antarctic, and that this region is already affected ". Rahmstorf pointed out other studies that suggest the same findings regarding changes in Antarctic groundwater.

However, one of the limitations of this research is that although scientists have found that deep water is not forming in two key Antarctic regions, they can not say when exactly the first change occurred in these areas. The researchers unfortunately do not have enough measurement data to determine it accurately, said Silvano, the author of the study. Thus, it is quite possible that the formation of deep water in these areas was stopped long ago, well before the modern period of intense global warming. This would make it more difficult to identify current events regarding human-caused climate change.

However, the mechanism detected by the study, in which glacier meltwater inhibits cold water on the surface, would probably continue to apply. Silvano said his main concern is, in addition to the melting ice, that Antarctica could begin to melt over its total surface if the climate continues to warm up further. He also said that if the formation of Antarctic groundwater slows down, the global consequences could be enormous: the process places heat and carbon dioxide deep beneath the surface of the ocean and without this phenomenon, heat and carbon dioxide could remain in the atmosphere.

In addition, there is the problem of sea-level rise, if the return between the ocean and the glaciers continues in this way: " The idea is that this mechanism of rapid melting and warming of the oceans has has already raised sea levels in the past, as for example during the last ice age, which saw a rapid rise in sea level of about five meters per century, "says Silvano. " We think this mechanism has been the cause of the rapid rise in water levels, " he added.

Source: https://trustmyscience.com/predictions-inquietantes-rechauffement-climatique/
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