The Antarctic ice sheet is melting. And that's not good news…
In its sixth assessment report, the Intergovernmental Panel on Climate Change (IPCC) indicates that in Antarctica, the temperature will continue to increase and the mass of the ice sheet will continue to decrease .
Sometimes, as is the case this year, the ice on the Rideau Canal in Ottawa is too thin to allow the skating rink to open.
On a larger scale, thousands of kilometers further south, in Antarctica, sea ice is also struggling to form. Indeed, Antarctic sea ice extent reached a record low on February 13.
While there has been a sharp decrease in Antarctic sea ice extent since 2016, the mass of the Antarctic ice sheet, it has been shrinking for a long time.
Expert in meteorology and polar climatology, I propose to shed light on the effect of global warming on Antarctica.
Antarctic sea ice concentration on February 13. The orange line represents the median sea ice extent corresponding to the period 1981-2010. Image courtesy of the National Snow and Ice Data Center, University of Colorado, Boulder (NSIDC).
Antarctica, the white continent
Antarctica, an ice-covered continent surrounded by ocean, holds 90% of world ice. This ice cover, named “ice cap” (ice sheet), is a mass of ice of terrestrial origin that is the result of the accumulation and compaction of snow over thousands of years. The seaward extension of the ice cap forms a floating ice shelf (ice shelf).
The Antarctic ice cap is made up of the Antarctic ice cap East and West Antarctic Ice Sheet. Most of the latter is anchored 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 is not spared from global warming. On the contrary. In a context of global warming, the increase in temperature at high latitudes is greater compared to the increase in the global average temperature. This phenomenon is known as “polar amplification”.
Ice-albedo feedback is one of the processes that explains this phenomenon. Indeed, the increase in temperature near the surface contributes to the melting of the ice, which contributes to the increase in temperature. For what ? Because the albedo (i.e. the fraction of solar energy that is reflected from a surface) of the ocean and underlying ground is less than that of ice.
< p>Over the past four decades, global warming has caused the average sea ice extent to decrease in the Arctic, but not in the Antarctic. If we do not find in the recent past a significant trend of reduction in the extent of the Antarctic mean sea ice, it is because the regional trends, positive and negative, compensate each other, and that there is a strong internal variability.
Antarctica is not spared from global warming. On the contrary. (Shutterstock)
However, the extent of Antarctic sea ice has decreased sharply since 2016. The decrease in sea ice cover area contributes to the increase in temperature (ice-albedo feedback), but it does not contribute to the sea level rise. As for the Antarctic ice sheet, its mass has been declining since at least the year 1990, with the greatest rate of loss occurring in the last decade.
In its sixth assessment report, the Intergovernmental Panel on Climate Change (IPCC) indicates that in Antarctica, the temperature will continue to increase and the mass of the ice sheet will continue to decrease. Note that the growth of the ice sheet is much slower than its retreat, which implies that if it continues to melt during this century, this melting will not be reversible on the human time scale.
With regard to Antarctic sea ice, the degree of confidence in its climate projections is low. Why? Among other things, because simulations with climate models do not capture the observed evolution of it well enough. We cannot therefore draw any conclusions.
Ice Sheet Collapse: What Consequences?
Sustained ice melt in the West Antarctic Ice Sheet could indicate that an unstable (self-reinforcing) retreat of the West Antarctic Ice Sheet it 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 “marine ice sheet instability”. If the bedrock on which the marine ice sheet sits slopes inward, the position of the grounding line (area from which the ice, which sits on the bedrock, begins to float) is unstable . Indeed, the thinning of the ice shelf causes the grounding line to retreat, which leads to an increase in the flow of ice from the ice sheet to the sea, and, subsequently, to the thinning of the ice shelf. And so on.
Diagram showing the process of marine ice sheet instability (“Marine Ice Sheet Instability”, MSI). Blue arrows indicate grounding line retreat, and white arrows indicate ice flow. Source: Pattyn, F. The paradigm shift in Antarctic ice sheet modelling. Common Nat 9, 2728 (2018). CC BY 4.0 license.
The complete melting of the West Antarctic Ice Sheet would cause a 3.3m rise in global sea level. Currently, the world is heading for a warming of 2.8°C by the end of of the century. Sustained warming between 2°C and 3°C would be enough to nearly wipe out this ice cap. But this phenomenon would take millennia.
The bottom line is that the melting of the Antarctic ice cap is and will be contributing for a long time to sea level rise, which will test humanity's ability to adapt. .
The rise in sea level by 2100 will particularly affect countries located in the tropics.
Like what, “what happens in Antarctica does not don't stay in Antarctica”.
Marta Moreno Ibáñez, PhD candidate in Earth and atmospheric sciences, University of Quebec in Montreal (UQAM)
This article is republished from The Conversation under a Creative Commons license. Read the original article.