Glaciers & Sea Level
Understand and project the mass balance of glaciers, ice caps, and the Greenland Ice Sheet, and their consequences for sea level rise
Global mean sea level is estimated to have risen by 1.2 to 1.9 mm per year over the 20th century and that rate rose to 3.0 ± 0.7 mm per year between 1993 and 2010 (Hay et al. 2015). For the period 2003- 2009, roughly 25 percent of the observed sea level rise appears to be due to surface mass imbalance of glaciers, excluding those of coastal Greenland and Antarctica (Gardner et al. 2013). This is similar to the contribution from ice sheets, of which roughly two-thirds is derived from Greenland Ice Sheet mass loss (Shepherd et al. 2012).
The increase in the net rate of ice loss from the Greenland Ice Sheet and other Arctic glaciers and ice caps (land ice) stems from warmer air temperatures that escalate melting on ice surfaces, and warmer ocean temperatures that increase calving of icebergs from marine-terminating glaciers. These forcings also modulate the dynamics of the ice, whose motion is governed by gravity and the constraints of surrounding topography. Although significant progress has been made in describing the current state of land ice, key questions remain about the specific processes that add and remove ice in the Arctic System, particularly regarding the interactions of the ice with the atmosphere and ocean. Given the rapidity with which the Arctic is seen to be warming, much may be learned about the future state of Arctic land ice by studying ongoing processes active in subarctic glacier systems.
As land ice and associated icebergs melt, the resultant effects include: contributions of freshwater and nutrients to the coastal zone with direct effects on marine ecosystems (Wadham et al. 2016) and coastal currents (Marsh et al. 2010); increasing storm-induced flooding associated with the rising sea levels (Tebaldi et al. 2012); reduced deep water formation in the ocean with consequences for climate (Weijer et al. 2012); and altered wind fields on various scales.
These effects, particularly those involving sea level rise and altered coastal currents, have regional and global implications. Regionally, the altered coastal currents will impact transport processes, such as spill response and search and rescue operations. Globally, coastal infrastructure, such as municipal gravity-fed sewage systems, subways, ports, military installations, roads, buildings, and property can be damaged by storm surge.
Present estimates of land ice loss rates and sea level rise rates involve large error bars, indicating the need for expanded observation and improved process understanding to allow enhanced modeling and projection over a variety of spatial and temporal scales. These processes are strongly influenced by the atmosphere above, the adjacent or underlying ocean, and the solid earth below the ice. Consequently, it is necessary to take a systems approach that accounts for atmospheric, oceanographic, and solid earth conditions and processes and that examines the interactions and feedbacks among these components.
The Land Ice and Sea Level Goal focuses on land ice conditions and processes and their consequences. Progress in the implementation of this Goal will also contribute to and benefit from research linkages to other aspects of this Plan. This Goal also addresses the call for policy-driven research that meets fundamental regional and national needs. For example, the changes that are occurring in the Arctic land ice cover affect the well-being of Arctic residents, the functioning of the marine environment, regional and national security, and impact and depend upon processes occurring far beyond the Arctic.
The work focuses on the following objectives