Glaciers and climate change

Glacial ice can range in age from several hundred to several hundreds of thousands years, making it valuable for climate research. To see a long-term climate record, scientists can drill and extract ice cores from glaciers and ice sheets. Ice cores have been taken from around the world, including Peru, Canada, Greenland, Antarctica, Europe, and Asia. These cores are continuous records providing scientists with year-by-year information about past climate. Scientists analyze various components of cores, particularly trapped air bubbles, which reveal past atmospheric composition, temperature variations, and types of vegetation. Glaciers preserve bits of atmosphere from thousands of years ago in these tiny air bubbles, or, deeper within the core, trapped within the ice itself. This is one way scientists know that there have been several Ice Ages. Past eras can be reconstructed, showing how and why climate changed, and how it might change in the future.

Satellite image of receding glaciers in BhutanThese glaciers in the Himalaya Mountains of Bhutan have been receding over the past few decades, and lakes have formed on the surfaces and near the termini of many of the glaciers. —Credit: Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument aboard NASA’s Terra satellite. Image provided by Jeffrey Kargel, USGS/NASA JPL/AGU, through the NASA Earth Observatory.

Scientists are also finding that glaciers reveal clues about global warming. How much does our atmosphere naturally warm up between Ice Ages? How does human activity affect climate? Because glaciers are so sensitive to temperature fluctuations accompanying climate change, direct glacier observation may help answer these questions. Since the early twentieth century, with few exceptions, glaciers around the world have been retreating at unprecedented rates. Some scientists attribute this massive glacial retreat to the Industrial Revolution, which began around 1760. In fact, several ice caps, glaciers and ice shelves have disappeared altogether in this century. Many more are retreating so rapidly that they may vanish within a matter of decades.

Scientists are discovering that production of electricity using coal and petroleum, and other uses of fossil fuels in transportation and industry, affects our environment in ways we did not understand before. Within the past 200 years or so, human activity has increased the amount of carbon dioxide in the atmosphere by 40 percent, and other gases, such as methane (natural gas) by a factor of 2 to 3 or more. These gases absorb heat being radiated from the surface of the earth, and by absorbing this heat the atmosphere slowly warms up. Heat-trapping gases, sometimes called “greenhouse gases,” are the cause of most of the climate warming and glacier retreat in the past 50 years. However, related causes, such as increased dust and soot from grazing, farming, and burning of fossil fuels and forests, are also causing glacier retreat. In fact, it is likely that the earliest parts of the recent glacier retreats in Europe were caused by soot from coal burning in the late 1800s.

Satellite image showing the retreat of Gangotri Glacier in the HimalayaThis false-color satellite image shows the Gangotri Glacier, situated in the Uttarkashi District of Garhwal Himalaya. Currently 30.2 kilometers (19 miles) long and between 0.5 and 2.5 kilometers (0.31 to 1.5 miles) wide, Gangotri glacier is one of the largest in the Himalaya. Gangotri has been receding since 1780, although studies show its retreat quickened after 1971. Note that the blue contour lines drawn here to show the recession of the glacier's terminus over time are approximate. Over the last 25 years, Gangotri glacier has retreated more than 850 meters (930 yards), with a recession of 76 meters (83 yards) from 1996 to 1999 alone. —Credit: NASA image by Jesse Allen, NASA Earth Observatory; based on data provided by the ASTER Science Team. Glacier retreat boundaries courtesy the Land Processes Distributed Active Archive Center.

The 1991 discovery of the 5,000 year-old "ice man," preserved in a glacier in the European Alps, fascinated the world (see National Geographic, June 1 1993, volume 183, number 6, for an article titled "Ice Man" by David Roberts). Tragically, this also means that this glacier is retreating farther now than it has in 5,000 years, and other glaciers are as well. Scientists, still trying to piece together all of the data they are collecting, want to find out whether human-induced global warming is tipping the delicate balance of the world's glaciers.