The Last Glacial Maximum (LGM), occurring around 21,000 years ago, marked the peak of the last ice age when massive glaciers covered significant portions of the Earth. These ice sheets, including the Laurentide in North America, the Fennoscandian in Europe, and others in Antarctica and Greenland, locked away immense volumes of water, drastically lowering global sea levels.
At the LGM, global sea levels were approximately 120–130 meters (394–427 feet) lower than present-day levels. This drop was a direct consequence of water being sequestered in ice sheets, estimated to cover about 25 million square kilometers (nearly 10 million square miles) of land. Coastal areas that are now submerged were dry land, connecting continents and creating migration pathways, such as the Bering Land Bridge between Asia and North America.
As the ice sheets began melting during the deglaciation period, approximately 19,000 years ago, the water they released into the oceans caused sea levels to rise. This process, termed post-glacial rebound or glacial isostatic adjustment (GIA), also affected Earth's crust. Regions previously compressed by ice began to rebound, while adjacent areas subsided, causing local variations in relative sea levels.
The melting continued over thousands of years, culminating around 8,000 years ago when sea levels stabilized near their current levels. However, the rebound effects and residual melting continue to influence sea level changes today.
The study of LGM glaciers and their impact on sea levels informs modern climate and geodetic science. Models like Ice-6G integrate LGM data to reconstruct past sea levels, providing a baseline for understanding current trends. By comparing ancient and modern sea levels, scientists gain insights into the rate and extent of ice-sheet melting and its implications for today’s rising seas.