Antarctica and its threats
Long-term implications
Zones of Antarctica
There are two ice sheets in Antarctica, with very different characteristics. [Figure 1]. The larger, the East Antarctic Ice Sheet (EAIS), covers most of the continent. The bedrock on which it sits lies above sea level in most places, and so it is termed a terrestrial ice sheet. In contrast, the smaller West Antarctica Ice Sheet (WAIS) is a marine ice sheet, because it has a bed that is below sea level over most of its area. The difference in bedrock elevation may seem minor, but it is in fact crucial as it is thought to determine the relative stability of the two ice sheets when considering the effect of climate change.
In addition, there is the Antarctic Peninsula, the finger of the continent pointing towards South America. The Antarctic Peninsula is one of the most rapidly warming places in the world. Air temperatures here have increased by 3°C over the last 50 years. This warming has been associated with the strengthening of the winds that encircle Antarctica, which in turn drives changes in oceanic circulation and increased upwelling of circumpolar deep water within the Southern Ocean. These are relatively salty, warm (3.5C) currents, which are now flowing onto the continental shelf and underneath the floating ice shelves of the West Antarctic Ice Sheet and Antarctic Peninsula. These changes in atmospheric air and ocean temperatures and circulation patterns are leading to dramatic, rapid changes in the glaciers of Antarctica, and especially in the summer months.
Figure 1. Antarctica - ice sheets and shelves
East Antarctica - the EAIS
The EAIS is thought to be relatively stable. Scientists have shown that during a natural warm period 2 to 5 million years ago the EAIS did not reduce significantly in size. It is so cold in this part of Antarctica that there is virtually no surface melting of the ice. Even if the temperature increased by a few degrees, it is still far too cold for surface melting and so the ice sheet would not shrink. Only if the temperature went up by huge amounts (tens of degrees) would it be possible for major melting to begin.
The amount of snowfall on Antarctica also depends on temperature. The warmer the air, the more moisture and snow it can hold. This means that if temperatures rose from the current very cold averages, the amount of snowfall on this area of Antarctica would increase and the EAIS may even get bigger. However, if temperatures rose further this effect will eventually be outweighed by the onset of melting.
The outcome is that in the next few decades, and perhaps even centuries, the increased snowfall on the EAIS may extract water from the oceans, and therefore partly offset sea-level rise from other sources - for example, melting of small ice caps (such as in Alaska) and thermal expansion of the oceans. Most scientists working on the Antarctic ice sheets think that the EAIS will not collapse or cause a significant sea-level rise for many centuries to come.
West Antarctica - the WAIS
Marine ice sheets such as the WAIS are thought to be inherently unstable. The fact that much of the ice sits below sea level means that it is sensitive to small rises in sea level, which can cause it to thin. Moreover, the WAIS is drained by several ice streams – fast moving ‘rivers’ of ice very different from the slow-moving ice of the rest of the Antarctic ice sheets on the EAIS. Because they move so fast and drain so much of the ice in the WAIS, the ice streams have the potential to rapidly increase the amount of ice being lost from the ice sheet to the ocean.
As the WAIS alone has the potential to raise sea level by 5m, scientists have been trying for decades to understand the ice sheet. Firstly, they have discovered that in the past some ice streams have both speeded up and slowed down by large amounts. This is important because it shows that the speed of ice streams can vary to such an extent that the amount of ice being drained from WAIS may change. The speeding-up of large ice streams has been measured recently in an area called the Amundsen Sea Embayment. Here three ice streams have accelerated and are discharging greater amounts of ice to the ocean than before. The reasons for this acceleration are now the subject of research, as well as the extent to which it may penetrate inland.
For example, a recent study published in Communications Earth & Environment has warned that only a small amount more ocean warming could trigger the collapse of WAIS. A multi-national team of scientists created model simulations going back 800,000 years to understand how the WAIS has responded to past changes in Earth's climate, as it shifted between cold glacial and warmer interglacial periods. The study suggests that the WAIS is now in an overshoot state, which should lead to a retreat contributing up to 4m sea-level rise with little (<0.25 °C) or even no deep ocean warming. Even without additional carbon emissions, 0.25 °C is already likely to occur within the next 50 years, thus resulting in substantial ice loss. The main driver of ice sheet melt and collapse is the rising ocean temperatures around Antarctica. The authors of the study fear that once the ice sheet tips into a collapsed state, its retreat becomes self-sustaining and practically irreversible.
The Antarctic Peninsula
The Antarctic Peninsula has experienced rapid warming in recent decades. There have been several impacts of climate change, ranging from physical effects such as the collapse of ice shelves and the retreat of glaciers, to biological effects such as changes to vegetation and movements in penguin colonies.
Across the whole Antarctic Peninsula, some 87% of glaciers are receding. Glaciers are also thinning, mostly in their ablation zones. These glaciers are also flowing faster because thinning in their lower regions reduces the effective stress at the bed, allowing them to move faster. At altitudes above 400m, glaciers are not thinning and may even be thickening. This is because snowfall is increasing across the Antarctic Peninsula (because warmer air can hold more moisture). However, this increased snowfall is not enough to offset surface lowering in the ablation zone.
Temperature records show pronounced warming here in recent decades. Readings have been taken at several sites including Vernadsky station in the western part of the peninsula. This station is a Ukrainian research base, which was once a British base (Faraday base). Since 1947, records have been kept by both sets of scientists. The temperature record from this station shows a warming of 2C since the 1950s with the warming trend strongest for the winter months. In addition, temperature measurements in the troposphere above the surface of Antarctica also show a warming during the winter of 0.5 – 0.7C per decade over the last 30 years. This is the largest tropospheric warming anywhere on Earth. In the ocean to the west of the Antarctic Peninsula monitoring has detected a 1C warming since the 1950s.
Climatologists suggest that this warming is due to increased atmospheric circulation, caused by the effects of climate change, which has brought more warm, moist air from further north down towards the peninsula. In the western part of the peninsula there is a strong correlation between sea-ice extent and winter air temperatures - when sea ice is less extensive, the winters are much warmer, and vice versa. This is because the sea ice acts as a cold lid on the ocean. When there is less sea ice, more heat can escape from the ocean (which has a temperature just above 0C) to warm the atmosphere (to approximately -10oC). The sea warms the air, which in turn may cause a reduction in sea ice, and so on. This is an example of a positive feedback loop.
The most pronounced impact has been the collapse of some Antarctic Peninsula ice shelves. Warmth has caused extra melting on the surface of the ice shelves, and eventually this leads to break up. Recent research using aerial photographs and satellite imagery has shown that nearly 90% of the glaciers in the peninsula have retreated since they were first measured. Ice shelves in this region began disintegrating in 1995, with the loss of Larsen A Ice Shelf. Larsen B Ice Shelf followed in 2002. These ice shelves collapsed during warm summers, when excess meltwater ponded on their surfaces. Rapid downward melting caused hydro fracture (large-scale cracking) and rapid production of icebergs.
A report produced by the British Antarctic Survey (BAS) stated that the Larsen C ice shelf is thinning from both its surface and beneath. The survey team found that the Larsen C ice shelf lost an average of 4m of ice, and had lowered by an average of 1m at the surface. They stated that two different processes are causing Larsen C to thin and become less stable. Air is being lost from the top layer of snow (called the firn), which is becoming more compacted - probably because of increased melting by a warmer atmosphere. Larsen C is also losing ice from below, probably from warmer ocean currents or changing ice flow. The report concluded that the ice shelf could collapse within a century, or sooner. As ice shelves support the glaciers that flow into them, when they are lost these glaciers are destabilised. The glaciers accelerate, thin and recede. The effect of this is again that more ice is directly transported into the oceans, making a direct contribution to sea-level rise.
Impacts beyond the immediate area – impact on ANZ
A new study has provided an assessment of how meltwater from the Antarctic Ice Sheet (AIS) affects Aotearoa/New Zealand’s (ANZ) climate. In both historical (1992–2020) and future (up to 2100) scenarios, the study finds that Antarctic meltwater causes significant cooling of the sea surface southeast of New Zealand, particularly in winter and spring. This cooling shifts the Subtropical (Antarctic) Front (a major ocean current boundary) northward and intensifies westerly winds south of the country.
As warming intensifies, the AIS is expected to lose mass - releasing vast volumes of cold freshwater into the Southern Ocean. This influx of meltwater not only cools surface temperatures but disrupts ocean circulation and atmospheric patterns. This meltwater also influences nutrient distribution, ocean productivity, and even fisheries. By partially reversing this shift, the AIS meltwater could unexpectedly alter marine ecosystems and food webs critical to New Zealand’s economy and biodiversity.
Another impact is the projected strengthening of winter westerlies south of New Zealand. These intensified winds are driven by sharper temperature gradients between polar and subtropical waters, reinforcing a feedback loop – meltwater cools the sea temperatures. Stronger westerlies enhance ocean mixing and further influence ocean current dynamics and climate variability - especially in the Southern Hemisphere.
At the heart of the study lies the concept of freshwater forcing - how the injection of low-salinity water (from melting ice) alters ocean circulation. When cold freshwater enters the Southern Ocean, it changes the water’s density and reduces its ability to sink—a process that would typically drive deep-ocean currents critical to global heat and carbon transport. This, in turn, changes surface temperature distributions and affects atmospheric circulation.