Guest Commentary by Mauri Pelto (Nichols College)

Preliminary data reported from the reference glaciers of the World Glacier Monitoring Service (WGMS) in 2018 from Argentina, Austria, China, France, Italy, Kazakhstan, Kyrgyzstan, Nepal, Norway, Russia, Sweden, Switzerland and United States indicate that 2018 will be the 30th consecutive year of significant negative annual balance (> -200mm); with a mean balance of -1247 mm for the 25 reporting reference glaciers, with only one glacier reporting a positive mass balance (WGMS, 2018).

A view of how alpine glaciers in the Pacific Northwest fit into the broader ecosystem (Megan Pelto, Jill Pelto).

I have spent 35 consecutive summers measuring mass balance on alpine glaciers, and more than 750 nights in a tent to record their response to climate change. A decade ago I described what was happening to alpine glaciers here at RC, but the continued signal of mass loss is inescapable and has been getting worse. The decadal mean annual mass balance of WGMS reference alpine glaciers was -171 mm in the 1980’s, -460 mm in the 1990’s, -500 mm for 2000’s and – 850 mm for 2010-2018.

Figure 1. Global Alpine glacier annual mass balance record of reference glaciers submitted to the World Glacier Monitoring Service, with a minimum of 30 reporting glaciers. Global values are calculated using only one single value (averaged) for each of 19 mountain regions in order to avoid a bias to well observed regions.

Just as people need to consume as many calories as the expend or they will lose mass, glaciers need to accumulate as much snow and ice as is lost to melt and calving icebergs in order to survive. After 30 consecutive years of alpine glacier mass loss it is clear that the “diet/lifestyle” of alpine glaciers is not healthy and as the climate they live in changes, alpine glaciers will continue a downward health spiral.

Alpine glaciers are recognized as one of most sensitive indicators of climate change. WGMS record of mass balance and terminus behavior (WGMS, 2017) providing a global index for alpine glacier behavior. This record illustrates a consistent signal from alpine glaciers around the world of significant mass loss and consequent retreat. Glacier mass balance is the difference between accumulation and ablation, reported here in mm of water equivalence (mm). Mean annual glacier mass balance in 2017 was -921 mm for the 42 long term reference glaciers and -951 mm for all 142 monitored glaciers. Figure 1 and 2 are graphs of global glacier mass change showing the annual balance for a set of global reference glaciers with more than 30 continued observation years for the time-period 1950-2018.

Figure 2. Decadal average mass balance of WGMS reference glaciers.

Glacier retreat reflects sustained negative mass balances over the last 30 years (Zemp et al., 2015). The increasing rate of glacier mass loss during a period of retreat indicates alpine glaciers are not approaching equilibrium and retreat will continue to be the dominant terminus response (Pelto, 2018). Ongoing global glacier retreat is currently affecting human society by increasing the rate of sea-level rise, changing seasonal discharge in glacier fed rivers, and increasing geo-hazard potential (Huss et al, 2017) (pdf). The recent mass losses 1991-2010 are due to anthropogenic forcing (Marzeion et al. 2014).

The cumulative mass balance from 1980-2018 is -21.7 m, the equivalent of cutting a 24 m thick slice off the top of the average glacier (Figure 1). The trend is remarkably consistent across regions (WGMS, 2017). WGMS mass balance from 42 reference glaciers, which have a minimum 30 years of record, is not appreciably different from that of all monitored glaciers at -21.5 m.

The number of reference glaciers is small compared to the total number of alpine glaciers (~200,000) in the world, but has proved to be a good approximation of global alpine glacier change. Marzeion et al (2017) compared WGMS direct observations of mass balance on a few glaciers to both remote sensing mass balance calculations based all alpine glaciers over the shorter period of available satellite data and climate driven mass balance model calculations and found that each method yields reconcilable estimates relative to each other and fall within their respective uncertainty margins. The WGMS record appears to have a slight negative bias compared to modeling and remote sensing approaches, but this bias has been much reduced with the regionalized approach now used by WGMS.

In 2018 exceptional glacier melt was noted across the European Alps, leading to high snowlines and contributing to large negative mass balance of glaciers. In the European Alps, annual mass balance has been reported from 17 glaciers in Austria, France, Italy and Switzerland. All 17 had negative annual balances, with 15 exceeding -1000 mm with a mean of -1640 mm. This continues the pattern of substantial negative balances in the Alps, which will equate to further terminus retreat. Of 81 observed glaciers in 2017 in Switzerland, 80 retreated, and only 1 was stable (Huss et al, 2018, [Fr]). In 2017, 83 glaciers were observed in Austria,; 82 retreated, and again only one was stable. Mean terminus retreat was 25 m, the highest observed since 1960 when mean length change reporting began (Lieb and Kellerer-Pirklbauer, 2018).

In Norway and Sweden, mass balance surveys with completed results are available for eight glaciers; all had negative mass balances with an average loss of -1420 mm w.e. All 25 glaciers with terminus observations during the 2007-2017 period have retreated (Kjøllmoen et al, 2018).

Figure 3. Taku Glacier transient snowline in Landsat 8 images from July 21, 2018 and September 16, 2018. The July 21 snowline is at 975 m and the September 16 snowline is at 1400 m. The average end of summer snowline from is m with the 2018 snowline being the highest observed since observations began in 1946.

In western North America data has been submitted from 11 glaciers in Alaska and Washington in the United States. All eleven glaciers reported negative mass balances with a mean loss of -870 mm. The longest mass balance record in North America is from Taku Glacier in Alaska. In 2018 the glacier had its most negative mass balance since the beginning of the record in 1946 and the highest end of summer snowline elevation at 1400 m. The North Cascade Range, Washington from 2014-2018 had the most negative five-year period for the region of the 1980-2018 WGMS record.

In the High Mountains of Asia (HMA) data was reported from ten glaciers including from China, Kazakhstan, Kyrgyzstan and Nepal. Nine of the ten had negative balances with a mean of -710 mm. This is a continuation of regional mass loss that has driven thinning and a slowdown in glacier movement in 9 of 11 regions in HMA from 2000-2017 (Dehecq et al. 2018).

Time series of glacier mass balance and temperature (as rendered by J. Pelto).

The key take away is the same for alpine glaciers around the globe, warming temperatures lead to mass balance losses, which leads to velocity slow down. Mass balance is the key driver in glacier response, and a sustained negative mass balance leads to thinning and retreat, which leads to a glacier velocity decline, whether the glacier is in the Himalayas, Alps or Andes.

References