What effects has climate change had on the Antarctic Ocean?
Antarctica and its ice, ocean, and ecosystems play a critical role in regulating the global climate. Together, they help slow global warming, drive important ocean currents, and contribute to the drawdown of millions of tons of carbon dioxide from the atmosphere. The climate crisis is disrupting these delicate systems. They are changing rapidly, with effects that will be felt around the world.
Over the past 50 years, the west coast of the Antarctic Peninsula has been one of the most rapidly warming parts of the planet. This warming is not only restricted to the land but can also be noted in the Southern Ocean. Upper ocean temperatures to the west of the Antarctic Peninsula have increased by over 1°C since 1955. It has now been established that the Antarctic Circumpolar Current is warming more rapidly than the global ocean as a whole. Studying climate change in Antarctica is important because it enables scientists to predict more accurately future climate change and provide information to politicians and policymakers.
The warming of the Antarctic Peninsula is causing changes to the physical and living environment of Antarctica. The distribution of penguin colonies has changed as sea ice conditions alter. The melting of perennial snow and ice covers has resulted in increased plant colonization. A long-term decline in the abundance of Antarctic krill in the SW Atlantic sector of the Southern Ocean may be associated with reduced sea ice cover. Large changes have occurred in the ice cover of the peninsula. Many glaciers have retreated, and ice shelves that formerly fringed the Peninsula have been observed to retreat in recent years, and some have collapsed completely.
Floating ice shelves are melting rapidly, raising concerns about sudden, uncontrollable sea level rise. The Antarctic Peninsula, a popular tourist destination, is one of the most rapidly warming places in the Southern Hemisphere, with average summer temperatures increasing by over 5°F (3°C) between 1970 and 2020. Since the 1970s, the Southern Ocean has absorbed as much as 75 percent of the excess heat created by humans and 40 percent of the carbon dioxide. Warmer, more acidic oceans are already impacting Antarctic ecosystems, with many penguin colonies shrinking and, in some cases, disappearing altogether.
Between 1971 and 2018, over 90% of thermal energy from global heating entered the oceans. The Southern Ocean absorbs the most heat by far—after 2005, it accounted for between 67% and 98% of all heat entering the oceans. The temperature in the upper layer of the ocean in West Antarctica has warmed 1°C (1.8°F) since 1955, and the Antarctic Circumpolar Current (ACC) is also warming faster than average. It is also a highly important carbon sink. These properties are connected to the Southern Ocean overturning circulation, which accounts for one-half of the global thermohaline circulation. It is so important that estimates on when global warming will reach 2°C (3.6°F) (inevitable in all scenarios where greenhouse gas emissions have not been strongly lowered) depend on the strength of the circulation more than any factor other than the overall emissions.
By 2100, net ice loss from Antarctica alone is expected to add about 11 cm (5 in) to global sea level rise. However, processes such as marine ice sheet instability, which describes the potential for warm water currents to enter between the seafloor and the base of the ice sheet once it is no longer heavy enough to displace such flows, and marine ice cliff instability, when ice cliffs with heights greater than 100 m (330 ft) may collapse under their own weight once they are no longer buttressed by ice shelves (which has never been observed and only occurs in some of the modeling), may cause West Antarctica to have a much larger contribution. Such processes may increase sea level rise caused by Antarctica to 41 cm (16 in) by 2100 under the low-emission scenario and 57 cm (22 in) under the high-emission scenario.
Some scientists have even larger estimates, but all agree it would have a greater impact and become much more likely to occur under higher warming scenarios, where it may double the overall 21st-century sea level rise to 2 meters or more. One study suggested that if the Paris Agreement is followed and global warming is limited to 2 °C (3.6 °F), the loss of ice in Antarctica will continue at the 2020 rate for the rest of the century. However, if a trajectory leading to 3°C (5.4°F) is followed, Antarctic ice loss will accelerate after 2060 and start adding 0.5 cm to global sea levels per year by 2100.
These effects highlight the interconnectedness of climate systems and the importance of the Antarctic region in global climate dynamics. Ongoing research and monitoring are essential to understanding the full extent of these changes and to developing strategies to mitigate their impacts.
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