Glacier National Park's Ice: From Ice Age to Little Ice Age to Human-Caused Melt

The Clements Glacier moraine at Logan Pass, 1928. Photo: W.C. Alden for the USGS.

Imagine a cold snap that lasts ten thousand winters. If more snow falls in those winters than melts in the summers, you are probably in an ice age. For thousands of years, the National Park Service says, the landscape of Glacier National Park was shaped by the natural advance and retreat of colossal glaciers that carved the U-shaped valleys visitors admire today. For about 10,000 years the Earth has been in a warmer interglacial period. Left to its own swings, the climate would be poised for another cold period soon, give or take a few thousand years, but human-caused climate change may already have postponed the next ice age.

Ice that comes and goes

Earth's temperature has risen and fallen naturally over the past 400,000 years, and the ice ages follow that pattern: when it was warm, glaciers retreated, and when it was cold, they advanced. The park's current glaciers probably formed about 7,000 years ago. They reached their largest size at the end of the Little Ice Age, a cold period that lasted from roughly 1300 to 1850, and then began to retreat as a warming trend set in. Logan Pass is an excellent place to see geologic evidence of the Little Ice Age up close.

Clements Glacier (just left of center), 1914. Photo: Morton J. Elrod.

The warming that began at the end of the 1800s melted many of the area's smaller glaciers. Clements Glacier, shown here in 1914, was near the modern trail to Hidden Lake Overlook. It largely melted away at the end of the Little Ice Age, without much influence from modern climate change. Other glaciers endured, though much smaller, and some of the larger ones might have found equilibrium with the climate of the 21st century. Instead, the article says, human-caused climate change is melting them away. Visitors who look at Jackson Glacier from Going-to-the-Sun Road stand in a valley carved by a Pleistocene glacier and see distant bedrock exposed as ice formed in the Little Ice Age retreats.

Natural change and human change

The ice began to retreat after the peak of the Little Ice Age, in the mid-1800s. The decrease since then is due to both natural and human-caused climate change, the article says, but by the 1990s the majority of the retreat could be attributed to human-caused climate change, and the retreat of recent decades increasingly so. Glaciers melt when more snow melts in summer than falls in winter. That gives scientists a chance to witness and study the power of climate change, natural and not. Glacier National Park has always been a place of change and, given time, it can adapt, but the rate of change seen today is fast enough to raise concerns about adaptation, for both ecosystems and societies.

The air was changed before

Burning fossil fuels gets much of the blame for altering the atmosphere, but many living things change the chemistry of the air. Plants take in carbon dioxide and release oxygen, and animals do the reverse. The oxygen we breathe today, the article notes, comes from colonies of cyanobacteria (blue-green algae) called stromatolites. Ancient stromatolite fossils are found throughout the park, including at Logan Pass, and through photosynthesis they produced the oxygen in the atmosphere, one tiny bubble at a time. Burning fossil fuels, which releases many tons of carbon dioxide, has changed the composition of the atmosphere in under 200 years, while it took stromatolites over a billion.

A geologist's hammer resting on a stromatolite fossil, 1951. Photo: Richard Rezak, USGS.

Sources

• National Park Service, Climate Change & Geologic History at Glacier National Park, part of the series Climate & History at Glacier National Park, which cites USGS publications and other studies of the park's glaciers; photographs credited to W.C. Alden and Richard Rezak for the USGS and to Morton J. Elrod; rewritten in hubnx's own words.