Storyboard: What is surface mass balance?

What is SMB and why is it important?

The surface mass balance (SMB) of Antarctica and Greenland represents the gain and loss of ice at the ice sheet surface due to snowfall, melt, runoff, erosion, and sublimation.

Understanding sea level rise is crucial, as meltwater runoff contributes to freshwater input into the oceans, leads to rising sea levels, and affects ocean circulation.

The surface mass balance is not the same as the total mass balance

The surface mass balance is only a part of the total mass balance of ice sheets. This total mass balance also accounts for melt at the bottom of ice shelves in warm seawater or the fracturing of floating ice shelves into icebergs.

Greenland’s future: more ice loss through melt

The surface mass balance of Greenland is dominated by snowfall, and the total surface balance has remained positive until now. However, the Greenland ice sheet is losing mass at an accelerating rate, contributing to global sea level rise.

The main cause of ice loss in Greenland is increased surface melting and meltwater runoff into the ocean due to the warming climate. In summer, the edges of the ice sheet reveal a darker, bare ice zone called the ablation zone, which absorbs more heat than the snow-covered ice sheet and accelerates melting.

Even though the surface mass balance is still positive, the total mass balance is negative: Greenland is losing 250–270 km³ of ice every year.

SMB in Antarctica: driven by very cold and dry conditions

In Antarctica, the surface mass balance is also dominated by snowfall. However, unlike in Greenland, the Antarctic ice sheet is losing mass mainly due to wind-driven erosion and sublimation in its cold, dry climate. Higher melt rates are observed in coastal regions on floating ice shelves, especially on the Antarctic Peninsula.

Even though the surface mass balance is positive, Antarctica is losing 110 km³ of ice every year, primarily due to basal melting.

In the future

In the future, our models predict a slight increase in precipitation over Greenland’s interior.

However, the significantly higher melt and runoff in the ablation zone will outweigh this, leading to a faster retreat of the ice sheet and further sea level rise. Greenland’s surface mass budget will become negative by the end of the century.

A "Greenlandification" of the Antarctic ice sheet is projected due to climate change, which will lead to more melt and increased runoff. Although an increase in snowfall might compensate for some of this, global climate models do not yet agree on future changes in snowfall and air temperature, introducing uncertainty into SMB estimates based on our regional climate models (in this case, RACMO).