Climate Change Indicators in the United States Technical Documentation Glaciers

Glaciers

Identification

1. Indicator Description

This indicator examines the balance between snow accumulation and melting in glaciers, and describes
how the size of glaciers around the world has changed since 1945. On a local and regional scale, changes
in glaciers have implications for ecosystems and people who depend on glacier-fed streamflow. On a
global scale, loss of ice from glaciers contributes to sea level rise. Glaciers are important as an indicator
of climate change because physical changes in glaciers—whether they are growing or shrinking,
advancing or receding—provide visible evidence of changes in temperature and precipitation.

Components of this indicator include:

• Cumulative trends in the mass balance of reference glaciers worldwide over the past 70 years
(Figure 1).

• Cumulative trends in the mass balance of three U.S. glaciers over the past half-century (Figure
2).

2. Revision History

April 2010: Indicator published.

December 2012: Updated indicator with data through 2010. Replaced Figure 1 with data from a

new source, the World Glacier Monitoring Service.

May 2014: Updated indicator with data through 2012.

June 2015: Updated indicator on EPA's website with data through 2014.

August 2016: Updated Figure 1 with data through 2015.

Data Sources

3. Data Sources

Figure 1 shows the average cumulative mass balance of a global set of reference glaciers, which was
originally published by the World Glacier Monitoring Service (WGMS) (2015). Measurements were
collected by a variety of academic and government programs and compiled by WGMS.

The U.S. Geological Survey (USGS) Benchmark Glacier Program provided the data for Figure 2, which
shows the cumulative mass balance of three U.S. "benchmark" glaciers where long-term monitoring has
taken place.

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4. Data Availability

Figure 1. Average Cumulative Mass Balance of "Reference" Glaciers Worldwide, 1945-2015

A version of Figure 1 with data through 2013 was published in WGMS (2015). Values through 2015 were
posted by WGMS at: http://wgms.ch/data databaseversions. Some recent years are associated with a
reduced number of associated reference glaciers (e.g., in 2015, 24 glaciers had available data instead of
the full set of 40). EPA obtained the data in spreadsheet form from the staff of WGMS, which can be
contacted via their website: http://wgms.ch/contact wgms. This indicator currently uses data from
WGMS database version doi:10.5904/wgms-fog-2015-ll.

Raw measurements of glacier surface parameters around the world have been recorded in a variety of
formats. Some data are available in online databases such as the World Glacier Inventory
(http://nsidc.org/data/glacier inventory/index.html). Some raw data are also available in studies by
USGS. WGMS maintains perhaps the most comprehensive record of international observations. Some of
these observations are available in hard copy only; others are available through an online data browser
at: www.wgms.ch/fogbrowser.

Figure 2. Cumulative Mass Balance of Three U.S. Glaciers, 1958-2014

A cumulative net mass balance data set is available on the USGS benchmark glacier website at:
www2.usgs.gov/climate landuse/clu rd/glacierstudies/default.asp. Because the online data are not
necessarily updated every time a correction or recalculation is made, EPA obtained the most up-to-date
data for Figure 2 directly from USGS. More detailed metadata and measurements from the three
benchmark glaciers can be found on the USGS website at:
www2.usgs.gov/climate landuse/clu rd/glacierstudies/default.asp.

Methodology

5. Data Collection

This indicator provides information on the cumulative change in mass balance of numerous glaciers over
time. Glacier mass balance data are calculated based on a variety of measurements at the surface of a
glacier, including measurements of snow depths and snow density. The net balance is the average mass
balance of the glacier from data collected over a glaciological year, the time between the end of the
summer ablation season from one year to the next. These measurements help glaciologists determine
changes in snow and ice accumulation and ablation that result from snow precipitation, snow
compaction, freezing of water, melting of snow and ice, calving (i.e., ice breaking off from the tongue or
leading edge of the glacier), wind erosion of snow, and sublimation from ice (Mayo et al., 2004). Both
surface size and density of glaciers are measured to produce net mass balance data. These data are
reported in meters of water equivalent (mwe), which corresponds to the average change in thickness
over the entire surface area of the glacier. Because snow and ice can vary in density (depending on the
degree of compaction, for example), converting to the equivalent amount of liquid water provides a
more consistent metric.

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Measurement techniques have been described and analyzed in many peer-reviewed studies, including
Josberger et al. (2007). Most long-term glacier observation programs began as part of the International
Geophysical Year in 1957-1958.

Figure 1. Average Cumulative Mass Balance of "Reference" Glaciers Worldwide, 1945-2015

The global trend is based on data collected at 40 reference glaciers around the world, which are
identified in Table TD-1.

Table TD-1. Reference Glaciers Included in Figure 1

Continent

Region

Glaciers

North America

Alaska

Gulkana, Wolverine

North America

Pacific Coast
Ranges

Place, South Cascade, Helm, Lemon Creek, Peyto, Columbia (2057)

North America

Canadian
High Arctic

Devon Ice Cap NW, Meighen Ice Cap, White, Melville South Ice Cap

South America

Andes

Echaurren Norte

Europe

Svalbard

Austre Broeggerbreen, Midtre Lovenbreen

Europe

Scandinavia

Engabreen, Alfotbreen, Nigardsbreen, Grasubreen, Storbreen,
Hellstugubreen, Remebesdalsskaaka (Hardangerjoekulen),
Storglaciaeren

Europe

Alps

Saint Sorlin, Sarennes, Argentiere, Silvretta, Gries, Stubacher
Sonnblickkees, Vernagtferner, Kesselwandferner, Hintereisferner,
Careser, Wurtenkees

Europe/Asia

Caucasus

Djankuat

Asia

Altai

No. 125 (Vodopadniy), Maliy Aktru, Leviy Aktru

Asia

Tien Shan

Ts. Tuyuksuyskiy, Urumqi Glacier No. 1

WGMS chose these 40 reference glaciers because they all had at least 30 years of continuous mass
balance records (WGMS, 2013). As the small graph at the bottom of Figure 1 shows, some of these
glaciers have data extending as far back as the 1940s. WGMS did not include data from glaciers that are
dominated by non-climatic factors, such as surge dynamics or calving. Because of data availability and
the distribution of glaciers worldwide, WGMS's compilation is dominated by the Northern Hemisphere.

All of the mass balance data that WGMS compiled for this indicator are based on the direct glaciological
method (0strem and Brugman, 1991), which involves manual measurements with stakes and pits at
specific points on each glacier's surface.

Figure 2. Cumulative Mass Balance of Three U.S. Glaciers, 1958-2014

Figure 2 shows data collected at the three glaciers studied by USGS's Benchmark Glacier Program. All
three glaciers have been monitored for many decades. USGS chose them because they represent typical
glaciers found in their respective regions: South Cascade Glacier in the Pacific Northwest (a continental

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glacier), Wolverine Glacier in coastal Alaska (a maritime glacier), and Gulkana Glacier in inland Alaska (a
continental glacier). Hodge et al. (1998) and Josberger et al. (2007) provide more information about the
locations of these glaciers and why USGS selected them for the benchmark monitoring program.

USGS collected repeated measurements at each of the glaciers to determine the various parameters
that can be used to calculate cumulative mass balance. Specific information on sampling design at each
of the three glaciers is available in Bidlake et al. (2010) and Van Beusekom et al. (2010). Measurements
are collected at specific points on the glacier surface, designated by a network of stakes, which facilitate
keeping a running tally of accumulation and ablation for each stake. Stake measurements along with
local temperature and precipitation data allow USGS scientists to derive glacier net and seasonal mass
balance estimates. For more information about these methods, see:
www2.usgs.gov/climate landuse/clu rd/glacierstudies/default.asp.

Data for South Cascade Glacier are available beginning in 1959 (relative to conditions in 1958) and for
Gulkana and Wolverine Glaciers beginning in 1966 (relative to conditions in 1965). Glacier monitoring
methodology has evolved overtime based on scientific reanalysis, and cumulative net mass balance
data for these three glaciers are routinely updated as glacier measurement methodologies improve and
more information becomes available. Several papers that document data updates through time are
available on the USGS benchmark glacier website at:
www2.usgs.gov/climate landuse/clu rd/glacierstudies/default.asp.

6. Indicator Derivation

For this indicator, glacier surface measurements have been used to determine the net change in mass
balance from one year to the next, referenced to the previous year's summer surface measurements.
The indicator documents changes in mass and volume rather than total mass or volume of each glacier
because the latter is more difficult to determine accurately. Thus, the indicator is not able to show how
the magnitude of mass balance change relates to the overall mass of the glacier (e.g., what percentage
of the glacier's mass has been lost).

Glaciologists convert surface measurements to mass balance by interpolating measurements over the
glacier surface geometry. Two different interpolation methods can be used: conventional balance and
reference-surface balance. In the conventional balance method, measurements are made at the glacier
each year to determine glacier surface geometry, and other measurements are interpolated over the
annually modified geometry. The reference-surface balance method does not require that glacier
geometry be redetermined each year. Rather, glacier surface geometry is determined once, generally
the first year that monitoring begins, and the same geometry is used each of the following years. A more
complete description of conventional balance and reference-surface balance methods is given in
Harrison et al. (2009).

Mass balance is typically calculated over a balance year, which begins at the onset of snow and ice
accumulation. For example, the balance year at Gulkana Glacier starts and ends in September of each
year. Thus, the balance year beginning in September 2013 and ending in September 2014 is called
"balance year 2014." Annual mass balance changes are confirmed based on measurements taken the
following spring.

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Figure 1. Average Cumulative Mass Balance of "Reference" Glaciers Worldwide, 1945-2015

The graph shows the average cumulative mass balance of WGMS's reference glaciers over time. The
number of reference glaciers included in this calculation varies by year, but it is still possible to generate
a reliable time series because the figure shows an average across all of the glaciers measured, rather
than a sum. No attempt was made to extrapolate from the observed data in order to calculate a
cumulative global change in mass balance.

Figure 2. Cumulative Mass Balance of Three U.S. Glaciers, 1958-2014

At each of the three benchmark glaciers, changes in mass balance have been summed over time to
determine the cumulative change in mass balance since a reference year. For the sake of comparison, all
three glaciers use a reference year of 1965, which is set to zero. Thus, a negative value in a later year
means the glacier has lost mass since 1965. All three time series in Figure 2 reflect the conventional
mass balance method, as opposed to the reference-surface method. No attempt has been made to
project the results for the three benchmark glaciers to other locations. See Bidlake et al. (2010), Van
Beusekom et al. (2010), and sources cited therein for further description of analytical methods.

In the past, USGS formally designated annual mass balance estimates as preliminary or final. USGS no
longer does this, choosing instead to continually refine and update mass balance estimates according to
the best available science and data. Accordingly, USGS provides new data to support regular updates of
this indicator with measurements that are comparable across glaciers. USGS is currently consolidating
glacier records to better harmonize calculation methods across space and time. Future updates of EPA's
indicator will reflect this harmonization.

7. Quality Assurance and Quality Control

The underlying measurements for Figure 1 come from a variety of data collection programs, each with
its own procedures for quality assurance and quality control (QA/QC). WGMS also has its own
requirements for data quality. For example, WGMS incorporates only measurements that reflect the
direct glaciological method (0strem and Brugman, 1991).

USGS periodically reviews and updates the mass balance data shown in Figure 2. For example, in
Fountain et al. (1997), the authors explain that mass balance should be periodically compared with
changes in ice volume, as the calculations of mass balance are based on interpolation of point
measurements that are subject to error. In addition, March (2003) describes steps that USGS takes to
check the weighting of certain mass balance values. This weighting allows USGS to convert point values
into glacier-averaged mass balance values.

Ongoing reanalysis of glacier monitoring methods, described in several of the reports listed on USGS's
website (www2.usgs.gov/climate landuse/clu rd/glacierstudies/default.asp), provides an additional
level of quality control for data collection.

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Analysis

8. Comparability Over Time and Space

Glacier monitoring methodology has evolved over time based on scientific reanalysis of methodology.
Peer-reviewed studies describing the evolution of glacier monitoring are listed in Mayo et al. (2004).
Figure 2 accounts for these changes, as USGS periodically reanalyzes past data points using improved
methods.

The reference glaciers tracked in Figure 1 reflect a variety of methods over time and space, and it is
impractical to adjust for all of these small differences. As a general indication of trends in glacier mass
balance, however, Figure 1 shows a clear pattern whose strength is not diminished by the inevitable
variety of underlying sources.

9. Data Limitations

Factors that may impact the confidence, application, or conclusions drawn from this indicator are as
follows:

1. Slightly different methods of measurement and interpolation have been used at different
glaciers, making direct year-to-year comparisons of change in cumulative net mass balance or
volume difficult. Overall trends among glaciers can be compared, however.

2. The number of glaciers with data available to calculate mass balance in Figure 1 decreases as
one goes back in time. Thus, averages from the 1940s to the mid-1970s rely on a smaller set of
reference glaciers than the full 40 compiled in later years.

3. The relationship between climate change and glacier mass balance is complex, and the observed
changes at a specific glacier might reflect a combination of global and local climate variations.

4. Records are available from numerous other individual glaciers in the United States, but many of
these other records lack the detail, consistency, or length of record provided by the USGS
benchmark glaciers program. USGS has collected data on these three glaciers for decades using
consistent methods, and USGS experts suggest that at least a 30-year record is necessary to
provide meaningful statistics. Due to the complicated nature of glacier behavior, it is difficult to
assess the significance of observed trends over shorter periods (Josberger et al., 2007).

10. Sources of Uncertainty

Glacier measurements have inherent uncertainties. For example, maintaining a continuous and
consistent data record is difficult because the stakes that denote measurement locations are often
distorted by glacier movement and snow and wind loading. Additionally, travel to measurement sites is
dangerous and inclement weather can prevent data collection during the appropriate time frame. In a
cumulative time series, such as the analyses presented in this indicator, the size of the margin of error
grows with time because each year's value depends on all of the preceding years.

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Figure 1. Average Cumulative Mass Balance of "Reference" Glaciers Worldwide, 1945-2015

Uncertainties have been quantified for some glacier mass balance measurements, but not for the
combined time series shown in Figure 1. WGMS (2013) has identified greater quantification of
uncertainty in mass balance measurements as a key goal for future research.

Figure 2. Cumulative Mass Balance of Three U.S. Glaciers, 1958-2014

Annual mass balance measurements for the three USGS benchmark glaciers usually have an estimated
error of ±0.1 to ±0.2 meters of water equivalent (Josberger et al., 2007). Error bars for the two Alaskan
glaciers are plotted in Van Beusekom et al. (2010). Further information on error estimates is given in
Bidlake et al. (2010) and Van Beusekom et al. (2010). Harrison et al. (2009) describe error estimates
related to interpolation methods.

11. Sources of Variability

Glacier mass balance can reflect year-to-year variations in temperature, precipitation, and other factors.
Figure 2 shows some of this year-to-year variability, while Figure 1 shows less variability because the
change in mass balance has been averaged over many glaciers around the world. In both cases, the
availability of several decades of data allows the indicator to show long-term trends that exceed the
"noise" produced by interannual variability. In addition, the period of record is longer than the period of
key multi-year climate oscillations such as the Pacific Decadal Oscillation and El Nino-Southern
Oscillation, meaning the trends shown in Figures 1 and 2 are not simply the product of decadal-scale
climate oscillations.

12. Statistical/Trend Analysis

This indicator does not report on the average rate of change in either figure, nor does it calculate the
statistical significance of these trends or provide confidence bounds. Josberger et al. (2007) note that
the rate of change appears to have accelerated for all three glaciers in Figure 2, which means that a
higher-order regression would likely be more appropriate than the standard linear regression that has
been applied in certain other indicators. WGMS (2015) provides average rates of change for specific
time periods, both regionally (Alaska, western North America) and worldwide. WGMS (2015) Table 2.2
also provides summary statistics for the distribution of results from the 40 reference glaciers worldwide
for the three most recent years, including the mean annual mass balance change, maximum, minimum,
and standard deviation.

References

Bidlake, W.R., E.G. Josberger, and M.E. Savoca. 2010. Modeled and measured glacier change and related
glaciological, hydrological, and meteorological conditions at South Cascade Glacier, Washington, balance
and water years 2006 and 2007. U.S. Geological Survey Scientific Investigations Report 2010-5143.
http://pubs.usgs.gov/sir/2010/5143.

Fountain, A.G., R.M. Krimmel, and D.C. Trabant. 1997. A strategy for monitoring glaciers. U.S. Geological
Survey Circular 1132.

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Harrison, W.D., L.H. Cox, R. Hock, R.S. March, and E.C. Petit. 2009. Implications for the dynamic health of
a glacier from comparison of conventional and reference-surface balances. Ann. Glaciol. 50:25-30.

Hodge, S.M., D.C. Trabant, R.M. Krimmel, T.A. Heinrichs, R.S. March, and E.G. Josberger. 1998. Climate
variations and changes in mass of three glaciers in western North America. J. Climate 11:2161-2217.

Josberger, E.G., W.R. Bidlake, R.S. March, and B.W. Kennedy. 2007. Glacier mass-balance fluctuations in
the Pacific Northwest and Alaska, USA. Ann. Glaciol. 46:291-296.

March, R.S. 2003. Mass balance, meteorology, area altitude distribution, glacier-surface altitude, ice
motion, terminus position, and runoff at Gulkana Glacier, Alaska, 1996 balance year. U.S. Geological
Survey Water-Resources Investigations Report 03-4095.

Mayo, L.R., D.C. Trabant, and R.S. March. 2004. A 30-year record of surface mass balance (1966-95) and
motion and surface altitude (1975-95) at Wolverine Glacier, Alaska. U.S. Geological Survey Open-File
Report 2004-1069.

0strem, G., and M. Brugman. 1991. Glacier mass-balance measurements: A manual for field and office
work. National Hydrology Research Institute (NHRI), NHRI Science Report No. 4.

Van Beusekom, A.E., S.R. O'Neel, R.S. March, L.C. Sass, and L.H. Cox. 2010. Re-analysis of Alaskan
benchmark glacier mass-balance data using the index method. U.S. Geological Survey Scientific
Investigations Report 2010-5247. http://pubs.usgs.gov/sir/2010/5247.

WGMS (World Glacier Monitoring Service). 2015. Global glacier change bulletin no. 1 (2012-2013).
Zemp, M., I. Gartner-Roer, S.U. Nussbaumer, F. Husler, H. Machguth, N. Molg, F. Paul, and M. Hoelzle
(eds.). ICSU (WDS)/IUGG (IACS)/UNEP/UNESCO/WMO. Zurich, Switzerland: World Glacier Monitoring
Service. http://wgms.ch/downloads/WGMS GGCB Ol.pdf.

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