Is Antarctica melting or not?

CLAIM

Antarctica isn’t melting but gaining ice. 

FACT

Antarctic sea ice extent shows no clear long-term trend since 1979 but land ice of Antarctica is melting away at an increasing rate which is a major contributor to rising sea levels. East Antarctica seemed to be stable but recent reports point to the fact that glaciers are not only rapidly melting in West Antarctica but East Antarctica too is witnessing rapid changes. The melting of glaciers in the Antarctic region is contributing to the elevation of global sea levels. 

WHAT THEY SAY

They claim that Antarctica isn’t melting. They point to the fact that the amount of sea ice around Antarctica has slightly increased to claim that ‘global warming’ is not happening. 

WHAT WE FOUND

The slight increase of sea ice around Antarctica in the last few decades (by about 1 percent per decade from 1979 to 2014) is a famous ‘rebuttal point’ often used in the climate change denialism narrative. They use this fact as proof to claim that Antarctica is not melting and that ‘global warming is not happening. 

To clear this confusion, one must understand the difference between sea ice and land ice. While the former plays almost no role in the rise of sea levels when it melts, the latter plays a crucial role in the elevation of sea levels by contributing huge amounts of extra water into the oceans by melting. 

ANTARCTIC SEA ICE

Antarctic sea ice is formed during the winter season-extending across the Southern Ocean in the winter and retreats to almost the coastline every summer. This phenomenon does not really contribute to the rising sea levels as the volume of water they displace as ice is about the same as the volume of water they add to the ocean when they melt. 

Figure 1: Coverage of sea ice in both the Arctic (Top) and Antarctica (Bottom) for both summer minimums and winter maximums. Source: National Snow and Ice Data Center

On the other hand, diminishing ice cover over the ocean also contributes to rising global temperatures. ‘White’ sea ice helps in reflecting the heat energy from the Sun back into space and helps in reducing global warming but unfrozen ‘black’ sea cannot do the same and instead absorbs heat leading to warmer seas. This results in a vicious cycle of ‘melting of more sea ice and production of more heat’. The warming of the seas contributes to sea-level rise because of the increase in the volume of water through thermal expansion. 

A slight increase in sea ice (by about 1 percent per decade from 1979 to 2014) around Antarctica was recorded by satellites in the last few decades. But recently there has been a sharp decline. Antarctic sea ice shrank to below 2 million square kilometers in 2022. It is the lowest recorded minimum extent since satellite recordings began 43 years ago.

ANTARCTIC LAND MASS/ICE

Antarctica is the fifth-largest continent in the world and makes up most of the Antarctic region, a cold and remote area in the Southern Hemisphere. It is a landmass covered on all sides by oceans. Antarctica consists of two main parts- East Antarctica (two-thirds of Antarctica) and West Antarctica. 

EAST ANTARCTICA – NO LONGER STABLE?

East Antarctica is a kind of cold desert at a considerable height with the ice sheet reaching an average thickness of over 2 km. If all of the ice in East Antarctica gets melted, it would lead to the sea level rising by about 60 meters. According to earlier studies, not much is happening in this part in terms of surface warming yet. But a recent report about an ice shelf collapse in East Antarctica, supposed to be the first in that region in human history, has got scientists worried. This also has raised questions about the previous assumptions about the stability of East Antarctica. Multiple recent studies have suggested that East Antarctica too is losing mass at an accelerated rate and is quite vulnerable to melting like West Antarctica.

WEST ANTARCTICA – DISAPPEARING FAST?

West Antarctica on the other hand is not a single continent but a series of islands covered by ice. They are not sitting on dry land but on the floor of the Southern Ocean and parts of it are more than a mile below sea level and the edges flow in floating ice shelves. The ice in this region, if it gets melted completely, would lead to the sea level rising by 5 to 7 metres. 

THE RETREAT OF WEST ANTARCTICA’S GLACIERS

The Amundsen Sea sector of West Antarctica with three glaciers in particular: Pine Island Glacier, Thwaites Glacier, and Smith Glacier is losing ice mass at an accelerating and alarming rate. Glacial discharge from the West Antarctic Ice Sheet in the Amundsen Sea sector is considered the primary contributor to the recent global sea-level rise. 

The two reasons for this glacial melt are:

1. Ocean-driven melting: When relatively warm water from the ocean interacts with the colder continental shelf

According to a study published in the science journal, Nature Geoscience, ice-ocean interactions are accelerating melting in West Antarctica. The analysis of Antarctica’s Smith, Pope, and Kohler glaciers in the study has revealed that the rapid pattern of glacial retreat has a connection with the high melt rates of ice floating in the Amundsen Sea sector.

The study reveals that the grounding line, which is defined as the line ‘where the ice moves off the land and begins to float’, of “Pope Glacier retreated 3.5 kilometers in 3.6 months for an average of nearly 12 kilometers per year in 2017. Between 2016 and 2018, the western portion of Smith Glacier retreated at 2 kilometers per year and Kohler Glacier at 1.3 kilometers per year.” The study found that “the main culprit in the rapid glacier retreat is the interaction of floating ice and seawater, particularly in newly formed cavities at the ice-ocean boundary.”

2. Atmospheric-driven melting: When the atmosphere drives surface melting of glaciers along the Antarctic coast

Near-surface air temperature at the northern tip of the Antarctic Peninsula reached 18.3 °C on 6 February 2020. This is the highest temperature ever recorded on the entire Antarctic continent. Such relatively higher air temperatures around the Antarctic Peninsula have led to a significant rise in meltwater ponding on the surface. This in turn is leading to ice shelf collapse as meltwater ponding on the surface leads to the thinned ice shelf getting propagated downwards initiating iceberg calving by hydrofracture.

CRUMBLING OF THE ICE SHELF 

Ice Shelves are actually part of a glacier that extends towards the ocean beyond the ‘grounding line’. They are said to be the most vulnerable in terms of the ‘warming’ seas. The ice shelves of West Antarctica’s glaciers collapsing rapidly is one of the primary reasons for their rapid retreat over the last few decades. On the other hand, a massive ice shelf about the size of New York City has recently broken off from East Antarctica. This is apparently the first ice shelf to break off East Antarctica in four decades of satellite observations.

Once the ice shelf collapses the glaciers that were protected by the ice shelves get exposed to the ‘warming’ sea and soon start disintegrating away into the ocean contributing to sea-level rise. Research has shown that after a rapid ice shelf retreat, the glacier behind it may accelerate as much as five times. 

LAND ICE AND SEA-LEVEL RISE

Figure 2: Total Antarctic land ice changes and approximate sea level contributions using a combination of different measurement techniques (IMBIE, 2017). Shaded areas represent measurement uncertainty. Source: https://skepticalscience.com/

The estimates of a recent change in the land ice of Antarctica show that land ice in the Antarctic region has increasingly melted over the last few decades thus contributing immensely to rising sea levels. The Antarctic Ice Sheets overall lost 2,720 giga-tonnes (GT) between 1992 and 2017 into the oceans, at an average rate of 108 Gt per year (Gt/yr). An annual average global sea-level rise of 1 mm is achieved by a reduction in land ice mass of 360 Gt/year. So an estimated average loss of 108 Gt per year (Gt/yr) will equate to a rise in average global sea levels by 0.3mm/yr. 

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