This week an international expedition set out for Mt. Logan, Canada’s highest mountain (and yes, it’s still Mt. Logan, not Mt. Trudeau) to attempt to travel through time: to look back 10,000 years to see how climate has changed over the millennia–and how human activities are affecting climate now.
Two Canadian scientists will climb to very Mt. Logan’s 5,959-metre peak and extract a 225-metre cylinder of ice from its glaciers. A core was taken in 1980, but the technology didn’t exist then to take one as long as will be taken this time–and the longer the ice core, the farther into the past you can look.
Obviously the scientists won’t be dragging a quarter-kilometre long icicle down the mountain intact, and no, they won’t just point it downhill and give it a shove, either. Instead, they’ll cut the core into one-metre slices, which will be left on the mountain until next spring, when they’ll be retrieved and shipped via refrigerated trucks and airplanes to Ottawa. There, scientists from the Unites States, Japan and Sweden will examine the ice.
Among other things, they’ll be able to tell how snowfall has varied from year to year. They may find volcanic ash from eruptions that took place around 4000 B.C. in the Aleutian mountain range in Alaska, or airborne pollen from Siberia, China or Japan. They may also find air bubbles containing samples of the atmosphere from thousands of years ago–analysis of such air bubbles is one way we know there is more carbon dioxide in the air now than there was before the Industrial Revolution.
The study of past climate is called paleoclimatology. Studying ice cores is one of the best ways to gather clues about ancient climates, but it’s not the only way.
In tropical climates, for instance, ice cores are hard to come by. Instead, scientists examine coral reefs. Corals build their skeletons from calcium carbonate, extracted from sea water. The calcium carbonate contains various forms of oxygen and different trace metals, depending on the temperature of the water in which it grew. By examining the coral skeleton, scientists can tell how warm the water was when it was formed.
As I mentioned, pollen is one of the things scientists will be looking for in the Mt. Logan ice core. Pollen can also be found preserved in the layers of sediment at the bottom of a body of water. Because each type of plant produces pollen grains with a distinct shape, fossil pollen tells scientists what kinds of plants were growing in the distant past–and that the climate must have been favorable to those species.
Tree rings are another source of information. As every schoolchild knows, trees produce one ring a year in temperate regions. The width, density and composition each ring are influenced by the climate that year. Since trees live hundreds, even thousands, of years, they provide a continuous, year-by-year record of climate change.
Ocean sediments are another source of data. Every year, between six and 11 billion tonnes of sediment settles to the bottom of the world’s oceans and lakes. By drilling out cores of this sediment and examining the chemicals and tiny fossils trapped in it, scientist can get an additional glimpse of past climate.
The favorite places to drill for ice cores are isolated mountain tops and in the Arctic and Antarctic, not just because that’s where the ice is, but also because their very isolation makes it less likely that local human activities have contaminated the site. Mount Logan, located on the Yukon-Alaska border, is ideal because very few people, except for a handful of climbers, have ever been anywhere near it. It’s also of interest because, although scientists have recently taken ice cores from Greenland and Canada’s eastern Arctic, they haven’t yet studied climate change on the Pacific Ocean side of North America — even though that’s where our weather comes from.
On the other hand, its isolation makes the expedition more difficult. High on the mountain, even in the summertime, storms are frequent and temperatures drop to -30. The air is dangerously thin and the ultraviolet radiation dangerously high.
It won’t be an easy or comfortable expedition, but the opportunity to examine a 10,000-year unbroken record of climate change is worth it, if it tells us more about how the North American climate has changed over the millennia–and helps us project how it will change, under humanity’s influence, in the future.