Antarctica’s ice loss is locked in, and extra snowfall won’t save it – that’s bad news for low-lying coastal areas elsewhere

Antarctica holds enough ice to raise global sea levels by about 190 feet (58 meters) if it all melted, though this would take centuries. Today, about 1 billion people live in coastal areas, with roughly 100 million living within 1 meter (3.3 feet) of sea level, making them highly vulnerable to flooding. Over the long term, Antarctica’s ice loss is the biggest unknown in predicting future sea-level rise, as scientists have debated whether the continent will gain or lose ice this century. The frozen continent’s fate depends on a chain of events linked to global warming, including ocean and air temperatures around Antarctica, the melting of ice shelves, and the speed at which glaciers slide into the sea. Ice shelves are floating extensions of the ice sheet that act as barriers, slowing the flow of glaciers behind them. When these shelves thin or collapse, glaciers can accelerate their movement toward the ocean. This process is already being observed in some parts of Antarctica.

Warmer air holds more moisture, which means Antarctica could receive more snowfall as global temperatures rise. In some climate models, this extra snowfall could theoretically offset ice loss from melting, leading to a net gain in the ice sheet’s mass. However, the article highlights that this scenario is unlikely. The study found that Antarctica will lose more ice than it gains this century, even if global warming is limited to 1.5 degrees Celsius (2.7 degrees Fahrenheit), the most ambitious goal of the 2015 Paris climate agreement. This conclusion is based on analyzing hundreds of thousands of possible future scenarios, using a machine learning model trained on simulations from the Ice Sheet Model Intercomparison Project (ISMIP6). The model helped researchers test combinations of assumptions about ice behavior and climate change that would otherwise be too computationally expensive to simulate individually.

The study emphasizes that reducing greenhouse gas emissions can slow Antarctica’s ice loss and the resulting sea-level rise. Every ton of greenhouse gas avoided today will reduce the amount of ice Antarctica loses this century, with benefits lasting for hundreds of years. In scenarios with very high emissions, the study projects that Antarctica alone could contribute up to 10 inches (25 centimeters) of sea-level rise by 2100. This amount is enough to permanently flood the homes of more than 10 million people living in low-lying coastal areas. The projections are based on data from satellites like NASA’s Grace, which measure changes in Earth’s gravity to track ice mass loss over time. The study also identifies three key physical processes that most influence future sea-level rise: how ice shelves respond to warming oceans, how ice slides over bedrock, and how quickly the ocean and air around Antarctica warm.

While the study provides a clearer forecast for Antarctica’s ice loss, it acknowledges that some processes are still missing from current simulations. For example, the study does not account for how ice cracks and breaks or how rivers and lakes beneath the ice sheet change over time. These factors could significantly alter the speed at which Antarctica’s ice reaches the sea and affect projections for coastal communities. The researchers used a machine learning model to speed up the testing of different assumptions, but the model cannot learn about processes not included in the original simulations. Despite these gaps, the study offers a faster way to test combinations of assumptions, providing a clearer basis for decisions that coastal communities must make now to adapt to rising sea levels.