This year, the ice Rideau Canalin Ottawa (Canada), is too fine enough to allow the opening of the ice skating rink.
Thousands of kilometers further south, in Antarctica, sea ice is also having a hard time forming. The extent of Antarctic sea ice beat a minimum record last February 13.
Although a sharp decline in Antarctic sea ice extent has been observed since 2016, the mass of the ice sheet has been declining for a long time.
the white continent
The Antarctica, an ice-covered continent surrounded by ocean, holds 90% of the world’s ice. This coverage, called “ice sheet” (ice sheets), is a mass of ice of terrestrial origin formed as a result of the accumulation and compaction of snow over thousands of years. The extension over the sea of the mantle constitutes a floating ice shelf (ice shelf).
The Antarctic Ice Sheet is made up of the East Antarctic Ice Sheet and the West Antarctic Ice Sheet. Most of the latter is supported on a rocky substratum located below sea level. Around Antarctica, the extent of sea ice, which forms from ocean water, increases in winter and decreases in summer.
Antarctica is warming faster
Antarctica has not been spared from climate change. Quite the contrary. In a context of global warming, the increase in temperature at high latitudes is stronger than the increase in global mean temperature. This phenomenon is known as “polar amplification”.
Ice-albedo feedback is one of the processes that explains this phenomenon. The increase in temperature near the surface contributes to the melting of ice, which contributes to the increase in temperature. Because? Because the albedo – that is, the fraction of solar energy that is reflected by a surface – of the ocean and the underlying soil is less than that of ice.
Over the past four decades, global warming has caused the decrease in mean extent of sea ice in the Arctic, but not in the Antarctic. The reason why we did not find a significant decreasing trend in the mean extent of Antarctic sea ice in the recent past is because the regional trends, positive and negative, cancel each other out, and because there is great internal variability.
However, the extension of the Antarctic sea ice has declined sharply since 2016. This reduction contributes to the increase in temperature (ice-albedo feedback), but not to the rise in sea level. As for the Antarctic ice sheetits mass has been declining since at least 1990, with the largest rate of loss occurring over the past decade.
In its sixth assessment reportthe Intergovernmental Panel on Climate Change (IPCC) indicates that the temperature will continue to rise in Antarctica and the mass of the ice sheet will continue to decrease.
It should be noted that the growth of the ice sheet is much slower than its retreat, which implies that if it continues to melt during this century, its disappearance will not be reversible on the human time scale.
As far as Antarctic sea ice is concerned, the degree of confidence in climate projections is low. Because? Among other reasons, because the simulations with climate models do not capture the observed evolution well enough. Therefore, we cannot draw conclusions.
Consequences of the collapse of the ice sheet
He continued melting of the West Antarctic ice sheet could indicate that an unstable (self-reinforcing) retracement has started or is imminent. But there is a lot of uncertainty about this phenomenon.
The mechanism that would explain this unstable retreat is known as “sea ice sheet instability”. If the rocky substratum on which the sea ice sheet rests is tilted inland, the position of the land line –the area from which the ice, which rests on the rocky substratum, begins to float– is unstable. The thinning of the floating ice shelf causes the retreat of the land line, which leads to an increase in the flow of ice from the ice sheet towards the sea and, consequently, to the thinning of the floating ice shelf. And so on.
He complete melting of the West Antarctic ice sheet would cause a 3.3m rise in global sea level. Currently, the world is heading towards a 2.8°C warming at the end of the century. A warming of between 2 °C and 3 °C would be enough to make this layer of ice disappear almost completely. But this phenomenon would take millennia.
What we must take away from all this is that the melting of the Antarctic ice sheet is contributing and will contribute for a long time to the rise in sea level, which is going to test humanity’s ability to adapt.
The rise in sea level between now and 2100 will particularly affect the countries located in the tropicswhich shows that “what happens in Antarctica does not stay in Antarctica”.
Marta Moreno IbanezPhD candidate in Earth and atmospheric sciences, University of Québec in Montreal (UQAM)
This article was originally published on The Conversation. read the original.
