Glacier and Ice Cap Assessments

Aaron Letterly
6 March 2018

Although there was a slight increase in the overall glacial mass balance in 2017, it will be the 38th consecutive year of negative mass balances globally, according to official reports by the World Glacier Monitoring Service (WGMS). The cumulative mass balance of all reference glaciers is now more than 20,000 millimeters (mm) of liquid water equivalent below 1970 totals (Figure 1). This is equivalent to a reduction of over 20 vertical meters of water spread out over the entire reference glacier area. Glacial mass balance decreased worldwide, likely reinforced by the third-highest annual surface temperatures on record in 2017 (NOAA). The few reference glaciers in Scandinavia and the Alps that had positive mass balances - an increase in ice since the last annual measurement - were outweighed and outnumbered by glaciers with significant ice loss. The average mass balance change for reference glaciers in 2017 was -886 mm, the third lowest since 1957.

Figure 1: Glacial mass balance (in mm w.e.) for all reference glaciers, worldwide. The shaded region around the zero line is the cumulative mass balance for reference glaciers relative to 1970, while the blue bars represent the number of reporting reference glaciers for that year (axis on far right). The black line shows the average reference glacier mass balance mean for each year. Data is from the World Glacier Monitoring Service. (Click to enlarge)

Figure 2 shows glacial mass balances for the 2016 and 2017 hydrological years, averaged together when measurements were available for both years. Selected reference glaciers in the European Alps, Scandinavia, and the North American Pacific Coast Range are shown in the figure. In some cases, mass balances of glaciers near one another were combined for clarity in Figure 2.

Figure 2: Glacial mass balance (in mme w.e.) for selected reference glaciers in the Alps (top), Scandinavia (middle), and North American Pacific Coast Range (bottom). Data is from the World Glacier Monitoring Service. (Click to enlarge)

In Greenland, a large amount of the ice lost every year is discharged from coastal glaciers, which slowly detach from the Greenland Ice Sheet and slide into the ocean. As ice and meltwater drain out to sea, coastal glaciers recede further inland and interior glaciers decrease in ice thickness, resulting in a loss of mass in regions of enhanced melting. Figure 3 shows the mass concentration anomaly over Greenland for summer 2016-2017 compared to the mean 2004-2009 mass concentration. As of this time, many regions along Greenland's coast have lost mass equivalent to nearly 1000 cm of glacial thickness, relative to their 2004-2009 average.

Figure 3: Total change in mass of Greenland (relative to 2004-2009) in centimeters of water equivalent for June 2016-2017. Data is based on monthly gravity changes from the GRACE satellite. GRACE data are available at http://grace.jpl.nasa.gov, supported by the NASA MEaSUREs Program. (Click to enlarge)

References

D.N. Wiese. 2015. GRACE monthly global water mass grids NETCDF RELEASE 5.0. Ver. 5.0. PO.DAAC, CA, USA. http://dx.doi.org/10.5067/TEMSC-OCL05

NOAA National Centers for Environmental Information, State of the Climate: Global Climate Report for Annual 2017, published online January 2018, retrieved on March 5, 2018 from https://www.ncdc.noaa.gov/sotc/global/201713.

Watkins, M. M., D. N. Wiese, D.-N. Yuan, C. Boening, and F. W. Landerer (2015), Improved methods for observing Earth's time variable mass distribution with GRACE using spherical cap mascons, J. Geophys. Res. Solid Earth, 120, doi:10.1002/2014JB011547.

Wiese, D. N., F. W. Landerer, and M. M. Watkins (2016), Quantifying and reducing leakage errors in the JPL RL05M GRACE mascon solution, Water Resour. Res., 52, 7490-7502, doi:10.1002/2016WR019344.

WGMS (2008): Global Glacier Changes: facts and figures. UNEP/UNESCO/WMO, World Glacier Monitoring Service, Zurich: 73 pp.