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 Climate Change Indicators: Glaciers
This indicator examines the balance between snow
accumulation and melting in glaciers, and it describes how
glaciers in the United States and around the world have
changed over time.
Key Points
On average, glaciers worldwide have been losing mass since
at least the 1970s (see Figure 1), which in turn has
contributed to observed changes in sea level (see the Sea
Level indicator). A longer measurement record from a smaller
number of glaciers suggests that they have been shrinking
since the 1940s. The rate at which glaciers are losing mass
appears to have accelerated over roughly the last decade.
All three U.S. benchmark glaciers have shown an overall
decline in mass balance since the 1950s and 1960s and an
accelerated rate of decline in recent years (see Figure 2).
Year-to-year trends vary, with some glaciers gaining mass in
certain years (for example, Wolverine Glacier during the
1980s), but the measurements clearly indicate a loss of
glacier mass over time.
Trends for the three benchmark glaciers are consistent with
the retreat of glaciers observed throughout the western
United States, Alaska, and other parts of the world.
Observations of glaciers losing mass are also consistent
with warming trends in U.S. and global temperatures during
this time period (see the U.S. and Global Temperature
indicator). |
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Background
A glacier is a large mass of snow and ice that has
accumulated over many years and is present year-round. In
the United States, glaciers can be found in the Rocky
Mountains, the Sierra Nevada, the Cascades, and throughout
Alaska. A glacier flows naturally like a river, only much
more slowly. At higher elevations, glaciers accumulate snow,
which eventually becomes compressed into ice. At lower
elevations, the “river” of ice naturally loses mass because
of melting and ice breaking off and floating away (iceberg
calving) if the glacier ends in a lake or the ocean. When
melting and calving are exactly balanced by new snow
accumulation, a glacier is in equilibrium and its mass will
neither increase nor decrease.
In many areas, glaciers provide communities and ecosystems
with a reliable source of streamflow and drinking water,
particularly in times of extended drought and late in the
summer, when seasonal snowpack has melted away. Freshwater
runoff from glaciers also influences ocean ecosystems.
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. If
glaciers lose more ice than they can accumulate through new
snowfall, they ultimately add more water to the oceans,
leading to a rise in sea level (see the Sea Level
indicator). The same kinds of changes occur on a much larger
scale within the giant ice sheets that cover Greenland and
Antarctica, potentially leading to even bigger implications
for sea level. Small glaciers tend to respond more quickly
to climate change than the giant ice sheets. Altogether, the
world’s small glaciers are adding roughly the same amount of
water to the oceans per year as the ice sheets of Greenland
and Antarctica. During the last two decades, they added more
water overall to the oceans than the ice sheets did. |
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About the Indicator
This indicator is based on long-term monitoring data
collected at selected glaciers around the world. Scientists
collect detailed measurements to determine glacier mass
balance, which is the net gain or loss of snow and ice over
the course of the year. A negative mass balance indicates
that a glacier has lost ice or snow. If cumulative mass
balance becomes more negative over time, it means glaciers
are losing mass more quickly than they can accumulate new
snow.
Figure 1 shows trends in mass balance for a set of 40
reference glaciers around the world that have been measured
consistently since the 1970s, including a few that have been
measured since the 1940s. Data from these reference glaciers
have been averaged together to depict changes over time.
Figure 2 shows trends for three “benchmark” glaciers: South
Cascade Glacier in Washington state, Wolverine Glacier near
Alaska’s southern coast, and Gulkana Glacier in Alaska’s
interior. These three glaciers were chosen because they have
been studied extensively by the U.S. Geological Survey for
many years and because they are thought to be representative
of other glaciers nearby.
This indicator describes the change in glacier mass balance,
which is measured as the average change in thickness across
the surface of a glacier. The change in ice or snow has been
converted to the equivalent amount of liquid water.
Indicator Notes
The relationship between climate change and glacier mass
balance is complex, and the observed changes at specific
reference or benchmark glaciers might reflect a combination
of global and local variations in temperature and
precipitation. Individual glaciers also vary in their
structure, flow, and response to climate. Slightly different
measurement and analysis methods have been used at different
glaciers, but overall trends appear to be similar.
Long-term measurements are available for only a relatively
small percentage of the world’s glaciers. This indicator
does not include the Greenland and Antarctic ice sheets,
although two decades of satellite data suggest that these
ice sheets are also experiencing a net loss of ice.
Continued satellite data collection will allow scientists to
evaluate long-term trends in the future.
Data Sources
The World Glacier Monitoring Service compiled data for
Figure 1, based on measurements collected by a variety of
organizations around the world. The U.S. Geological Survey
Benchmark Glacier Program provided the data for Figure 2.
Historical data, as well as periodic reports and
measurements of the benchmark glaciers, are available on the
program’s website at:
https://2.usgs.gov/climate_landuse/clu_rd/glacierstudies/default.asp.
Technical Documentation
Download related technical information PDF |
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 Figure
1. Average Cumulative Mass Balance of "Reference"
Glaciers Worldwide, 1945–2015
This figure shows the cumulative change in mass balance of a
set of “reference” glaciers worldwide beginning in 1945. The
line on the upper graph represents the average of all the
glaciers that were measured. Negative values indicate a net
loss of ice and snow compared with the base year of 1945.
For consistency, measurements are in meters of water
equivalent, which represent changes in the average thickness
of a glacier. The small chart below shows how many glaciers
were measured in each year. Some glacier measurements have
not yet been finalized for the last few years, hence the
smaller number of sites.
Data sources: WGMS, 20163 |
 Figure
2. Cumulative Mass Balance of Three U.S. Glaciers,
1958–2014
This figure shows the cumulative mass balance of the three
U.S. Geological Survey “benchmark” glaciers since
measurements began in the 1950s or 1960s. For each glacier,
the mass balance is set at zero for the base year of 1965.
Negative values indicate a net loss of ice and snow compared
with the base year. For consistency, measurements are in
meters of water equivalent, which represent changes in the
average thickness of a glacier.
Data sources: O’Neel et al., 2014;4 USGS, 20155 |
 Reference
Map
Reference map for figure 2 above. |
 Photographs
of McCall Glacier, Alaska, 1958 and 2003
Sources: Post, 1958;6 Nolan, 20037 |
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EPA Page |
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This is the
EPA page for this topic. To see if the Trump
administration has changed the EPA page, simply click the
link and compare the information with this page. If you
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comment. Thanks. |
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Additional Climate Change Information |
Climate Change and Carbon Dioxide
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of climate change
and carbon dioxide.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice. |
Carbon Dioxide and Climate Change
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of carbon dioxide
and climate change.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice. |
Environmental Group Warns Earth's Health at Risk
(Beginner - Listening,
reading)
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The English is
spoken at 75% of normal speed.
Great English listening and reading practice.
A report by the World Wildlife Fund looked at thousands of animal populations
and found they have dropped significantly in 40 years. |
Sea Levels Rising at Fastest Rate in 3,000 years
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of climate change.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice.
A group of scientists say sea levels are rising at record rates. Another group
found that January temperatures in the Arctic reached a record high. |
Capturing CO2 Gas Is Not Easy
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of climate change.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice.
Most scientists agree that carbon-dioxide gas is partly to blame for climate
change: rising global temperatures. But capturing the CO2 gas released by power
stations is costly and difficult. |
Growth, Climate Change Threaten African Plants and
Animals
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of climate change.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice.
Researchers believe Africa may lose as much as 30 percent of its animal and
plant species by the end of this century. |
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