I spend much of my time in the high Arctic. The mythological place of ice, midnight sun and endangered polar bears. By now everybody knows what the Arctic sea ice cover looks like and how fast it's shrinking, and satellite images of the globe with ever decreasing ice cover have become common fare in even the most popular of newspapers. Each summer tourists land on these shores in great numbers. They venture out of their comfort zone to see for themselves what it's all about and with them come the journalists, the nature conservationists and the politicians. Most go on day trips to glacier fronts. They go by boat through the fjords and they look at old maps and talk about how the ice has retreated since the map was made and how beautiful it is and how sad it is for the polar bears.
We take students on similar trips. Not because we want them to experience the Arctic before it is gone, but because they need to go to the same fjords to study the modern processes and geology in their curriculum. Because professors are not mean we also go on short "sightseeing" excursions like up close to glacier fronts, and we talk about the same things other people to do when they experience this dramatic play of nature for the first time. We also talk about former positions of the ice margin, but rather than concluding that the ice has retreated two kilometers since 1963 and therefore we are sad, we talk about how glaciers behave and what ice marginal positions mean.
Many glaciers in this particular corner of the world are what we call surging glaciers. It means they accumulate snow (which eventually turns to ice) over many years (often decades), while moving very slowly. At some point the imbalance between the accumulation on the upper part of the glacier and the mass loss near the front will be so extreme that gravity and the sliding capacity along the base of the ice force the ice mass to move forward. Surging glaciers can move forward at incredible speeds of up to 100 m/ day or more than a km in a year. They alternate between the surging phase that commonly lasts a few years and the quiescent phase that lasts for decades. During the quiescent phase glaciers retreat to an "equilibrium position" and build up towards a new surge. In the high Arctic where modern science came with the polar explorers of the late 19th and early 20th century very little is known about the past behaviour of surging glaciers. For many glaciers it is not known whether they are surging at all. Surging glaciers often leave remarkable traces in the landscape in the shape of moraines. The force involved in the surge allows for the ice to push up "slices" of the bed and stack them in front of the glacier. When the ice retreats the moraines remain. Dating organic material (C-14 dating) or Quartz or feldspar mineral grains in sand (luminescence dating) can tell us about the age of past surges. Sometimes they also leave traces in the sea floor like plough marks where rock fragments attached
to the base of the glacier have scraped the sea floor.
Surging glaciers are dependent on the ability to slide across the bed. Large glaciers and ice masses like the Greenland and Antarctic inland ice are wet at the base because the weight of the ice allows the ice mass to reach its pressure melting point. Smaller glaciers in cold areas are often what we call polythermal. It means the glacier snout is frozen to the ground, but the thicker ice mass in the hinterland is wet at the base. Surging glaciers are often polythermal. When Arctic glaciers decrease in size they become cold based or perenially frozen to the ground. Cold based glaciers don't really move. It is possible that many glaciers that were surging in the past aren't so anymore. It is also likely that some of the glaciers that surge today will not continue to do so.
In historical terms, glaciers used to be bigger. A global cold phase, "The Little Ice age" lasted from the 17th to the 19th century and is confirmed from historical records from harvest to diseases and narratives about cold winters and wet summers. It did however not begin and end simultaneously and different regions have reacted differently to the climatic fluctuations that characterized this time interval. It seems from temperature records that the north Atlantic snapped out of the cold phase relatively late, maybe as late as the 1920's-1930's. Ice margins from the maximum position of glaciers during The Little Ice Age are still dominant in the landscape. In areas with permafrost, moraines degrade very slowly. Some people have suggested that glaciers are still adapting to the temperature changes 70-80 years ago. This does not suggest that no mass loss is going on today, just that it is difficult to distill the modern change from historical change when standing on a ship experiencing the scenery for the first time.
Each year glaciologists camp out on the glaciers in order to measure thicknesses, ice temperature and isotopic composition, trace gases and other evidence of "the state of the ice". Practically all of them come to the conclusion that most glaciers in the world loose mass rapidly, and the well documented studies should leave no doubt that the heat has been turned on and that ice is melting. So what am I complaining about? I am complaining about the lack of talk about how the glaciers really move and what it is we see in the landscape. The moraine five kilometers in front of the modern glacier margin is not a sad sign of the ice retreat, but a sign of a not climate related natural phenomenon called glacier surge and the retreat from the Little Ice Age moraine is partly an adaptation to warming over the past 100 years. The real signs of climate warming such as the thinning of the glacier, change from polythermal to cold-based glaciers and shorter duration and thinner sea ice cover may be less photogenic, but all the more important.
Let me end by saying that I do
"believe in global warming induced by humans and I do
think we should do everything we can to turn or diminish the global warming trend. I'm all for higher gas prices, environmentally friendly cars and public transportation and I think it will at some point be considered unethical to fly everywhere and use bargain air tickets. I am also deeply conflicted about this need to always point out that I'm not against global warming when pointing out inaccuracies in terminology or public lingo about the state of the Arctic. As someone who studies palaeoclimate rather than present climate these issues come up a lot when some study or other suggests that things were different in the past than we think.
This post is submitted to the geology carnival "The Accretionary Wedge
" on "Favorite geological misconceptions".
(I admit that this post does not conform with my own views on what geology is as discussed recently on Clastic Detritus, but it does have a lot to do with something I encounter regularly in my professional life as a geologist)