Glaciers are dynamic systems -- they move!
The terminus (front edge) of a moving glacier represents the equilibrium point of warm air trying to push back the edge (glacier retreat, or shrinkage) and the forward velocity of the ice pushing downhill (glacier advance, or growth).
The velocity of glacier movement depends on the varying friction along the glacier's path, and variable snowfall on the glacier over time.
The ice melting at the edge, and sometimes chunks breaking off into the ocean, is the oldest ice in the glacier.
The snowfall history, from the time of the oldest ice on the edge through today (could be hundreds or thousands of years) affect the current velocity of the glacier.
Glaciers respond to many variables:
(1) Atmospheric temperature,
(2) Precipitation (snowfall),
(3) Ice thickness,
(4) Slope,
(5) Ice temperature (polar vs. temperate),
(6) Land-based vs. tidewater,
(7) Size (cirque glaciers vs. long valley glaciers
vs. ice sheets),
(8) Amount of subglacial meltwater, and
(9) Response time to climate change.
With all the variables involved, some glaciers will be retreating while others are advancing!
And a glacier could retreat in spite of falling temperatures, or advance in spite of increasing temperatures.
Glacier behavior varies a lot.
Attributing a glacier's response to climate change requires more than just observing or measuring an advance or a retreat.
Some glaciers are more sensitive to climate changes than others.
Long, thick, valley glaciers close to an ocean (like the glaciers on volcanos in the North Cascade Range) tend to most reflect climate change.
Cirque glaciers nearby do not.
Glaciers:
(1) Strongly advanced from about 1880 to 1915
(nearly advanced to "Little Ice Age" positions),
(2) Strongly retreated from about 1915 to about 1950,
(3) Strongly advanced from about 1950 to 1980, and
(4) Retreated from about 1980 to 2000.
These fluctuations correspond roughly to global climate changes.
The 1915-1950 glacial retreat was stronger than the 1980 to 2000 retreat—that's why glaciers are still a half mile or so down valley from their 1950 retreat positions.
If “global warming” is to blame for alleged glacial retreat in recent decades, then why hasn’t the huge East Antarctic Ice Sheet retreated in the 21st century?
In fact, its mass has grown.
Melting ice in the Northern Hemisphere could also be caused by dark industrial soot, now coming mainly from China and India,
Soot darkens ice and snow, which increases its albedo (dirty snow and ice absorb more solar energy than pristine snow and ice).
Melting ice could also be caused by a decrease in cloudiness without any change in air temperatures.
The rapid retreat of some alpine and valley glaciers in the past is on south-sun-facing slopes, with little change on northern slopes in the shade.
Warmunists have cherry-picked the Jakob Isbrae glacier -- the most quickly retreating glacier on Earth since 1850 -- as their "poster boy" to "prove" humans are warming the planet.
That's a bogus claim.
They don't mention most of that glacier's retreat happened BEFORE 1950.
But the "age of manmade CO2" didn't start until 1940.
There's not much overlap.
A similar glacier movement can be seen in Glacier Bay National Park, in Alaska .
That glacier was discovered in 1794, when there was only a small indentation on the shoreline.
Explorers who returned in 1879 found the Ice had retreated 48 miles from the ocean.
By 1916 the edge of the glacier was 65 miles from the ocean.
Since 1916 the glacier has retreated at a slower pace, in spite of global warming!