What Mount Logan ice cores tell us about past climate

In the Northern Hemisphere, long climate records have been obtained from ice cores drilled in Greenland or from the Canadian, Norwegian and Russian Arctic islands. In contrast, little is known of the long-term climate history of the Pacific northwest region. Ice cores from Mount Logan may help to fill this knowledge gap.

The new ice core from the summit of Mount Logan (PR Col).
Ice Core
Photo Natural Resources Canada



As shown in this figure, the new ice core from the summit of Mount Logan (PR Col) contains a climate record which is strikingly different from that obtained in cores from Arctic ice caps.

The climate record from the Mount Logan summit (PR Col) ice core.
Temperature Histories
Photo Natural Resources Canada



These graphs show variations in the ratio of heavy and light isotopes of oxygen in ice crystals, from successive slices (layers) of ice cores. In Greenland and the Canadian Arctic, this ratio is mostly determined by the air temperature at the time of snowfall, so these records can be read like temperature histories.

The lowest graph shows the temperature history reconstructed from the Greenland (GRIP) deep ice core which covers the last ~115,000 years. (Reference to GRIP record). The last Ice age (called ‘Wisconsin’ in North America and ‘McConnell’ in Yukon) came to an end about 11,550 years ago and the present interglacial period (the Holocene) began.

The middle panel shows the Holocene time period at a larger scale. The temperature histories from the Greenland and eastern Arctic ice cores are similar: warmer than today from ~10,000 to 7000 years ago, followed by a long-term cooling trend. Scientists think the long-term cooling is caused by a changes in Earth’s orbit (see Milankovitch cycles). This is the long, natural slide of the Earth's climate towards the next ice age.

In the Northern Hemisphere, the late Holocene was marked by a generally cold and stormy period that lasted from the ~14th to mid- or late 19th century, often called the Little Ice Age. During this period, glaciers advanced and sea-ice cover spread out. Since then, temperatures have been on the rise. The warming accelerated in the late 20th century, quite probably due to the buildup of greenhouse gases in the Earth's atmosphere.

(Note: It would be misleading to point to the graph as showing the recent global warming, because at the scale of the graph one can not distinguish between the post-Little Ice Age warming and the late 20th century trend. This has to be told in the caption, as I did above)

The climate record from the Mount Logan summit (PR Col) ice core is shown by the topmost graph. The same parameter (oxygen isotope ratio) and scales are used, yet this record is obviously very different than those from Arctic ice cores (middle panel). So why does the Mount Logan ice-core record show a different pattern? Learn more

[The differences we are talking about here are differences in the Holocene postglacial record: They have nothing to do with the relative timing of continental glaciations in the St-Elias mountains]