Examining Glacial Mass Balance
by Daniel Bailey
(Michigan, United States)
Glacial Length Changes
Let's examine the question of glacial mass balance, shall we?
Firstly, the majority of reference glaciers the world over are thinning and retreating.
Over time, more and more of the glaciers the world over have gone into retreat and decline. As one gets nearer the present time, this effect becomes more pronounced and more uniformly evident the world over.
In fact, when viewed as a group whole, the sum of glaciers everywhere tells a story of decline, retreat and loss of mass balance (few "healthy" glaciers remain the world over). And the trend has become increasingly negative over time.
Glacier National Park Will Be Without Glaciers
Based on current trends, glacier recession models predict that by 2030, Glacier National Park will be without glaciers.
In 2012—for the 23rd consecutive year—mountain glaciers worldwide lost more mass through melting than they gained through new snow accumulation. Considering all glaciers for which we have at least some records, mountain glaciers and ice caps have lost an amount of ice equivalent to slicing a 54-foot-thick slab (16.5 meters) off the top of an average glacier, and the rate of loss has accelerated in each of the past three decades.
In fact, nearly 70% of world glacier melt since 1991 is due to human activity.
"the anthropogenic signal is detectable with high confidence in glacier mass balance observations during 1991 to 2010, and the anthropogenic fraction of global glacier mass loss during that period has increased to 69 ± 24%"
Marzieon et al 2014 - Attribution of global glacier mass loss to anthropogenic and natural causes
"The cumulative glaciers and ice caps (GIC) surface mass balance (SMB) was negative for all regions. The SMB contribution to sea level rise was largest from Alaska and smallest from the Caucasus. On average, the contribution to sea level rise was 0.51 ± 0.16 mm sea level equivalent (SLE) yr−1 for 1979–2009 and ~40% higher (0.71 ± 0.15 mm SLE yr−1) for the last decade, 1999–2009."
Mernild et al 2014 - Northern Hemisphere Glacier and Ice Cap Surface Mass Balance and Contribution to Sea Level Rise
Sea Level Rise
Just over a third of sea level rise is due to steric/thermal expansion. Just over half is from ice sheet mass losses. The rest is other stuff.
|Component Linear trend and uncertainty*||(mm/year)|
|Total observed global sea level rise|| 2.10 ± 0.16|
|Thermal expansion|| 0.80 ± 0.15|
|Land ice loss|| 1.09 ± 0.26|
|Groundwater depletion|| 0.26 ± 0.07|
|Other terrestrial water storage factors|| -0.37 ± 0.25|
|Total of known contributions|| 1.78 ± 0.36|
|Residual|| 0.32 ± 0.39|
*Error estimates are one standard deviation
Table 2: Contributions to sea level rise; Adapted from Church et al. 2011