This is part of a series on the effects of climate change.
How fast are glaciers and sea ice melting?
Although somewhat similar, glaciers and sea ice differ in several ways. Glaciers are formed on land when accumulated snow is compressed over many years, forming layers of ice that are constantly moving under their weight. From the Southern Andes to the Himalayas, glaciers are retreating around the world at increasing rates. Between 2000 and 2019, Alaska accounted for a quarter of glacial mass loss worldwide, losing almost 70 billion metric tons per year during the period. Meanwhile, the Greenland periphery lost over 35 billion metric tons of ice annually during the analyzed period, contributing the second-largest share of global glacier mass loss.By contrast, sea ice forms entirely in the ocean when seawater freezes and floats on the ocean surface. The average global sea ice extent has diminished over the past four decades, with Arctic sea ice disappearing at a far greater rate. In September 2020, the average sea ice extent in the Northern Hemisphere reached a low of four million square kilometers, down from almost eight million square kilometers in September 1980.
The effects of melting
Sea ice plays a crucial role in regulating the global climate as their large bright surfaces reflect sunlight back into space, helping to keep the planet cooler. When the surface area becomes smaller, less heat is reflected, and more heat is absorbed at the surface. This results in warmer temperatures that, in turn, aggravate melting, in a vicious feedback loop. Melting sea ice also represents a threat to the wildlife that depends on it, such as polar bears and walruses.In contrast, the melting of land ice (glaciers and ice sheets) critically impacts sea level. An increase in ocean mass – the weight of the ocean – contributed to an average sea level rise worldwide of 2.1 millimeters per year between 2002 and 2019. Scientists estimate that regardless of the emissions scenario, land ice will continue to contribute to sea level rise until the end of the century, adding as much as 30 centimeters in a high emissions scenario, impacting coastal regions across the globe.