Glaciers and climate

Why do glaciers get so much attention when it comes to climate change?

Surely there are consequences of climate change that are worse than the disappearance of glaciers, such as drought and lack of food and water? Among other things, glaciers are our most important water reservoir. As much as 70% of all fresh water on Earth is stored in the form of ice, and glaciers thus provide a stable water supply for many people. In addition, glaciers around the world are one of our best climate archives.

Glaciers are sensitive indicators of climate change. Photo: Trygve Snøtun.

Glaciers give us important information about past climate

There are several ways in which glaciers can be used as climate archives. A glacier is formed by several years of snow accumulation. The snow is transformed into ice through melting and freezing processes and compression. In between the ice crystals, air bubbles from the last time the snow/ice was in contact with the atmosphere are trapped. By drilling ice cores, we can take samples of these air bubbles and find out how the atmosphere has been composed in the past and how the amount of greenhouse gases such as carbon dioxide and methane has changed over time.

Another way to study ice cores is to look at the oxygen isotope composition of the water molecules that make up the ice. The isotopic composition of precipitation reflects the temperature when the precipitation occurred. This can tell us something about how the temperature has changed over time. It is also possible to determine the age of the samples being analyzed by counting annual layers in the snow/ice on the large inland ice sheets, where light layers are the winter and dark layers are the summer. These annual layers can also tell us about changes in precipitation.

Are all glaciers equally interesting?

Ice cores are best suited where there is little snow melt and continuous snow accumulation. In addition, there should be as little ice movement as possible at the drilling sites. Therefore, the best locations are at the center of a glacier/ice cap where it is very cold. The large ice sheets in Greenland and Antarctica are particularly important for reconstructing temperature, precipitation and atmospheric composition back in time. Ice cores over 3000 meters long have been recorded from both ice sheets, but because there is less precipitation in Antarctica, the longest time series are obtained there. Today, Greenland has managed to go back over 120,000 years with these ice cores, while Antarctica has managed to go back a full 800,000 years.

The figure shows how the CO2 concentration in the atmosphere and temperature have fluctuated over the last 800,000 years. The results are found after examining ice cores retrieved from 3,060-3,270 meters down in the Antarctic ice sheet. The figure is modified from Lüthi et al. 2008.

The extension of glaciers reflects the regional or local climate

The smaller glaciers are also important in understanding the climate. Changes in glacier extent tell us something about changes in climate. Since glaciers are mainly controlled by winter precipitation and summer temperature, changes in these climate parameters will be reflected by the glacier. Heavy snow and/or low temperatures cause glaciers to grow, while less snow and/or high summer temperatures cause glaciers to melt. Today, both changes in the glacier front and mass balance are measured on many glaciers, both in Norway and the rest of the world.

Advance or retreat of the glacier front is a reaction to positive/negative mass balance, but due to different reaction times, there may be several years' delay between the measured positive mass balance and an advance in the glacier front. There are many methods for calculating glacier extension further back in time than there are measurements. Dating of moraine ridges and analysis of glacial sediments in lakes and fjords can provide valuable information about earlier glacier extent, and thus about climate back in time.