Human activity has driven retreat of Antarctica's fastest melting glacier

Human activity has driven retreat of Antarctica's fastest melting glacier

Human-driven climate change significantly intensified the retreat of the Pine Island Glacier during the twentieth century, according to new research. The glacier, which drains a large portion of the West Antarctic Ice Sheet into the Amundsen Sea, stands as one of the single biggest contributors to global sea level rise.

The study, published in The Cryosphere, is the first to directly attribute changes in a major Antarctic outlet glacier to human activities. Research led by scientists at King’s College London and the British Antarctic Survey indicates that greenhouse gas emissions increased the retreat of the glacier by around 18-20% since the 1940s, adding several kilometres to its landward withdrawal.

Lead author Dr Alex Bradley of the Department of Geography stated that the scale of retreat observed over the industrial era is very unlikely to have occurred without human influence.

"Our results show that climate change made the retreat of the Pine Island Glacier substantially worse,"

Dr Bradley, study lead author, via kcl.ac.uk

He added that without sustained warming of the surrounding ocean since the mid twentieth century, the glacier would not have retreated as far as it has.

While attribution studies have commonly linked heatwaves, floods, and mountain glaciers to human-driven warming, applying these techniques to Antarctic glaciers has been more challenging. Dr Bradley noted that the novelty of this work is the quantitative demonstration of how human influence altered the course of a major Antarctic glacier.

Geological records suggest the Pine Island Glacier began retreating rapidly in the 1940s, likely due to stronger intrusions of warm ocean water beneath its ice shelf. This study found that human-driven ocean warming, thought to have begun in the 1960s, enhanced that retreat. Using a model that simulates glacier behaviour via observed changes in ice thickness and retreat, researchers compared scenarios with and without human-driven global warming.

Simulations that excluded human influence showed around 4 km less grounding-line retreat by 2015. This difference represents just under one-fifth of the observed retreat.

Irreversible Tipping Points

Separate research published in Nature Climate Change reveals that the Pine Island Glacier passed a tipping point within the last 80 years, undergoing an irreversible retreat. Researchers from Northumbria University and Bangor University combined numerical model simulations with real-world satellite observations to confirm this unstable retreat occurred between the 1940s and 1970s.

During this period, the glacier detached from a seabed ridge and was 40km more advanced than its present-day position. It retreated rapidly until it temporarily stabilized on a shallow part of the seabed in the late 1980s. By the early 1970s, the glacier had retreated to a point where it could not recover its original mass and position, even during colder conditions.

Professor Mattias Green of Bangor University said the trigger for this historical retreat was possibly an episode of warm ocean water entering the area. Hilmar Gudmundsson, Professor of Glaciology at Northumbria University, warned that the stabilization of the retreat after a few decades of ice loss was potentially a case of luck due to the bedrock topography under the Amundsen Sea.

Professor Gudmundsson cautioned that ice loss in this region should not be viewed as a gradual response to global warming, but as something that loses ice on its own accord at an accelerated rate when pushed too far.

Global Implications and Future Outlook

The Pine Island Glacier and its neighbor, the Thwaites Glacier, are referred to as the underbelly of the West Antarctic ice sheet. Mira Adhikari, an Ice Sheet Modeller at the British Antarctic Survey, stated that these results add to evidence that human-driven climate change affects even the most remote regions of the planet.

Models suggest the Pine Island Glacier may briefly stabilize later this century upon encountering a ridge in the bedrock. However, researchers warn this pause will likely be temporary if warming continues. Human influence is expected to become the dominant driver of retreat again in the twenty-second century.

Dr Brad Reed, a Research Fellow in Ice-Ocean Modelling at Northumbria University, stated that his model predicts further irreversible and fast periods of mass loss in the future unless global warming is halted.

Dr Bradley emphasized that because ice sheets respond slowly, the impacts of current emissions will continue to shape Antarctic ice loss for centuries.

Ongoing efforts to understand these risks include the £4 million TiPACCs (Tipping Points in the Antarctic Climate System) project, led by Northumbria University, which investigates the probability of sudden, large changes in sea-level contributions from the Antarctic Ice Sheet.