Greenland ice sheet

The Greenland ice sheet, often called the GIS or GrIS, is the second-largest body of ice on Earth.

It covers approximately 80% of the island of Greenland. This massive structure is incredibly thick, reaching its maximum thickness at its center. The ice sheet is also very wide near its northern edge at a latitude of 77°N. This ice sheet is a vital part of the Earth's climate system. It acts as a massive reservoir of freshwater on our planet. Understanding its movement and stability is essential for predicting future sea levels.

Ice sheets form through a process called glaciation. This happens when a local climate is cold enough for snow to accumulate every year. As new snow layers pile up, their immense weight compresses the layers underneath. Over hundreds of years, this pressure turns the snow into firn, which then becomes solid glacier ice.

The sheer weight of this ice causes it to flow slowly like a very thick liquid. This movement continues unless the ice hits a large obstacle, such as a mountain. In Greenland, many mountains near the coast prevent the ice from flowing freely into the Arctic Ocean. However, the ice can reach the sea through gaps in the mountains called outlet glaciers. These glaciers regularly release ice into the ocean through a process known as ice calving.

Greenland's icy history is very long and complex. While large glaciers have existed there for at least 18 million years, they were likely much smaller in the past. A single, massive ice sheet first covered most of the island about 2.6 million years ago. Since that time, the ice sheet has grown and contracted many times. There have been 11 distinct periods where the ice sheet grew large enough to flow over high mountains.

The oldest known ice on the sheet is roughly 1 million years old. This history shows that the ice sheet is a dynamic system that responds to changing global temperatures.

Geological changes helped create the current ice sheet. About 10 million years ago, during the middle Miocene, the land in West and East Greenland began to rise. This uplift created high surfaces between 2,000 and 3,000 meters above sea level. Later, during the Pliocene, another uplift created surfaces between 500 and 1,000 meters. These changes increased orographic precipitation, which is rain or snow caused by air moving over mountains. This extra moisture, combined with cooler temperatures, allowed the ice to accumulate and stay. Eventually, as atmospheric carbon dioxide levels dropped to between 280 and 320 ppm, the separate ice caps connected into one giant sheet.

Scientists use ice cores to study these ancient changes. An ice core is a long cylinder of ice drilled from deep within the sheet.

These cores contain tiny air bubbles that act as a snapshot of the ancient atmosphere. By analyzing these bubbles, researchers can see the gas composition of the air from thousands of years ago. They can also study oxygen isotopes to learn about past water cycles and precipitation patterns. These records even show evidence of ancient volcanic eruptions and changes in vegetation. Even human history is recorded here, such as lead production from the Roman Empire.

Today, the ice sheet is experiencing rapid changes due to anthropogenic greenhouse gas emissions. The ice sheet is currently the warmest it has been in at least 1,000 years. It is also losing ice at the fastest rate in at least 12,000 years.

Since 1996, annual snowfall has not been enough to replace the melting ice. Between 2010 and 2018, the ice sheet lost an average of 286 gigatonnes of mass every year. This mass loss has been accelerating, with half of the net loss observed between 1992 and 2018 occurring in just eight years. As of 2022, the ice sheet had been losing mass for 26 consecutive years.

The melting of the Greenland ice sheet has serious consequences for the entire world. As the ice turns to water and flows into the ocean, it contributes to global sea level rise. If the Paris Agreement goals are met, melting alone could add significant centimeters to sea levels by the end of this century. If emissions are not reduced, the contribution could be much higher. In a worst-case scenario, the melting could add even more to the rise by 2100. If the entire ice sheet were to melt, global sea levels would rise by about 7 meters. If global temperatures continue to rise, the ice sheet could disappear entirely within 1,000 to 10,000 years.