G10 Geography Cold Environments
At the end of the last ice age 10,000 years ago, the last glaciers retreated from Britain and Ireland.
How do we know? There were no cameras and maybe not even people.
Today we can recognise the extent of the ice masses from erosional and depositional features they left behind. The polar climate experienced by Britain and Ireland was gradually replaced by the temperate climate we enjoy today but, over a wider time frame, the thousands of years of relative warmth are a minor blip and most glaciologists believe that we are heading towards another ice age.
The study of glaciations is made difficult by the vast amounts of time involved and the complexity of climatic cycles themselves.
This is made worse by recent evidence of global warming.
Are glaciers in retreat, or are they advancing? The evidence is not complete. Today many glaciers in the world are retreating (e.g. the Robert Scott glacier in Antarctica), but in other places (e.g. the Svaritsen glacier in Norway) there have been big advances.
In the longer term, we are most probably heading for another glacial phase but the timing and nature of the event are too far distant to be determined with real accuracy.
However, regions of the planet characterised by polar climates today are obvious enough to allow us to study the effects of glacial and periglacial processes. The geological record also shows the impact of ancient glaciations dating back to the Precambrian period.
Periglacial - that means what?
On the edge of a glacial area.
Ice ages began as a result of global climatic changes. Every 200 to 250 million years during the Earth’s history, there appear to have been major periods of glacial activity.
During the Quaternary period, which began just over 2 million years ago, the ice began to spread from the polar ice caps, particularly into North America and northern Europe.
In fact, sediments taken from ocean floor cores suggest that the advance was more complex than previously thought, with up to 20 glacials (cold periods) and interglacials (warmer periods).
The fluctuation in global temperatures during these times was no more than 6°C.
At its greatest extent the ice covered nearly a third of the Earth’s surface and only 18,000 years ago, at the peak of the last advance, ice covered the UK from the Bristol Channel across to Norfolk. (Picture 1)
Reasons for the climatic fluctuations are thought to include:
• changes in the Earth's position in space, its orbit and tilt
• variations in sunspot activity changing the amount of solar radiation received by the Earth
• changes in the amount of volcanic dust affecting the amount of radiation trapped by the atmosphere
• trapping of carbon dioxide by the oceans reducing the total amount in the atmosphere and thus cooling the planet
• variations in ocean currents.
Glaciers as systems (picture 2)
Glaciers are masses of ice (and debris) which are continually changing and may be seen as an open system with inputs (e .g. snow and avalanches) which add to the mass, and outputs (e.g. evaporation and meltwater) which decrease the mass.
Near the source of a glacier, inputs generally exceed outputs and this is known as the zone of accumulation. There are several interrelated factors that combine to help develop glaciers. At higher altitudes there is more precipitation (the orographic effect), mainly in the form of snow. New snow is highly reflective, absorbing less heat and therefore melting more slowly.
Stronger winds at high altitudes cause snow to be blown into hollows and basins so that snow accumulates. As temperatures are low, sublimation (the change in state from solid to vapour) and other losses are low, and meltwater is likely to refreeze.
The zone of ablation is found at lower altitudes towards the snout of the glacier, and is where outputs exceed inputs. Here there is less snowfall and temperatures are higher, resulting in outputs in the form of melting (surface, basal and within the glacier), sublimation, evaporation and calving.
The dividing line between the two zones is called the firn (or equilibrium) line. Gravity moves ice continually down to the equilibrium line, replacing that lost at the snout by ablation.
The difference between the total accumulation and total ablation for the whole of the glacier over one year is called the glacial budget or net balance. This is calculated for the balance year which runs from autumn to autumn, when summer ablation will have reduced the total ice mass to a minimum.
There is a positive winter balance and a negative summer balance; for example a typical Alpine glacier will lose ice at over 10m a year through melting and is normally replenished by ice flowing from above. when the amounts of accumulation and ablation are equal the glacier is said to be in a steady state. The snout may not move but the ice is passing through it like on a conveyor belt.
Glaciers may take many years to react to changes in accumulation or ablation but where snowfall is exceptionally heavy the glacier may react quickly and surge forward.
Rates of movement of flowing glaciers are extremely variable, with the fastest parts flowing at anything between 50m and 400m a year (even faster if they end in the sea). Flow rates of 1000m a year or more are seen in large ice streams in Antarctica and outlet glaciers in Greenland.
Glacier size and shape
Ice mass classifications can vary in detail. Here is a standard list, from smallest to the largest:
Niche glaciers (picture 3) are small patches of glacier ice found on upland slopes. They are most prevalent on north-facing slopes in the northern hemisphere. They have relatively little effect on topography.
Cirque (corrie) glaciers (picture 4) are small ice masses on mountain slopes which gradually erode armchair- shaped hollows. If they develop to be too large for the hollow, they spill over the lip to feed a valley glacier.
Valley glaciers (picture 5) are larger masses of ice that flow from ice fields or a cirque and usually follow pre- glacial river valleys, developing steep sides as they erode their course.
Piedmont glaciers (picture 6) are large lobes of ice formed when glaciers spread out. They may merge on reaching lowland areas and escape the confines of their valleys.
Ice caps (picture 7) are huge, flattened, dome-shaped masses of ice that develop on high plateaus. They are similar to an ice sheet, but are less than 50,000 km2 in area. Above 50,000 km2 they are known as ice sheets. The Antarctic ice sheet attains a thickness of over 4000 m.
Ice shelves are extensions of ice sheets that reach out over the sea. These shelves of floating ice can be up to 1000m thick but diminish to around 500 m on average at the edge where icebergs calve.
Cold Environments Part 2
A study into how and why global distribution of cold environments has changed and continues to change.
The distribution of cold environments has changed throughout time. It is certain is that there have been repeated glacial periods separated by warmer interglacial times.
Alpine (picture 8): high altitude areas within mountain ranges where glaciers and small ice caps can be found.
Periglacial (picture 9): Bordering a glacial area but not actually covered by ice all year round, having similar climatic and environmental characteristics.
Polar (picture 10): Regions around the poles of the earth that are permanently covered with ice. During the last glaciation, the ice was at its maximum extent about 18,000 years ago. At this time there was a continental ice sheet across most of North America with many glaciers in the mountains of the west. The North of Europe had areas glaciated as well as areas of high altitude e.g. the Himalayas. Most of Greenland was covered in ice, one of the largest areas. The world has been covered by glaciers, and evidence shows that 17 glacial cycles have advanced to different areas. But since the end of the last ice age, there has been a retreat of glaciers and ice sheets.
Across the globe there have been many cold environments which have experienced change.
Glaciers can exist at high altitudes because the air is thinner, so less heat is absorbed. For example, Huascaran, in the Andes mountains is over 6,500m above sea level, yet only 9° south of the equator.
The Grinnell Glacier is located in Montana, USA and has been subject to change in its size and depth.
Polar ice caps are areas of high latitude that receive little sun light, making it extremely cold. These high latitude areas include The Arctic, Greenland, Siberia and Norway. Alaska is an area that contains many glaciers that are subject to change.
Periglacial literally means ‘on the edge of ice’. These are cold, treeless locations but they are not ice covered. Typically, their temperature is below 3°C. Periglacial areas have frozen ground or permafrost.
Canada contains permafrost areas that are changing.
The Grinnell Glacier (picture 11)
Repeated photography over the decades since 1850 clearly show that glaciers throughout the Glacier National Park, Montana such as Grinnell Glacier are all retreating. The larger glaciers are now approximately a third of their former size when first studied in 1850, and numerous smaller glaciers have disappeared completely. Only 27% of the 99 km² area of Glacier National Park covered by glaciers in 1850 remained covered by 1993.
The Grinnell glacier has lost an estimated 90% of its mass: in 1850 the glacier measured 2.88km². By 1993 this had reduced to 0.88km². Future predictions expect that by 2030 the glacier will have melted away.
Changes to Canadian permafrost
Historical temperature trends show a warming of nearly 2°C during the last century in the western Canadian Arctic. In addition, extreme conditions such as the El Niño year of 1998 resulted in mean annual temperatures 5°C warmer than the average conditions.
Climate change since the end of the Little Ice Age, especially during the 20th century, has induced degradation of permafrost in most of Canada: From the 1850s to the 1990s, the area underlain by permafrost was reduced by 5.4%.
• For those areas where permafrost existed in all the years throughout the period 1850–2002, the mean depth to the base of permafrost became shallower by 3m.
• The mean active layer thickness decreased by 0.21m, or 34%.
• The mean depth to permafrost table decreased by 0.39m.
It is anticipated that ground temperatures will continue to increase with future warming, permafrost levels will therefore decrease even more. Reduced permafrost means reduced albedo, meaning more heat being absorbed resulting with more thawing.
Glaciers in the Northwest United States have been shrinking, under pressure from rising temperatures, longer summer seasons, and a rising snowline.
Studies by the Climate Impacts Group at University of Washington show regional temperature has been 1.5°C warmer in the 20th century, with decreasing mountain snow pack, and earlier spring runoff.
Alaska’s glaciers, 34,000 square miles of ice, are receding at twice the rate previously thought and beginning to contribute significantly to sea level rise, according to studies in Science journal.
There are thousands of glaciers in Alaska, though only a relative few of them have been named. Of the nineteen glaciers of the Juneau Ice field, eighteen are retreating, and one, the Taku Glacier, is advancing. Eleven of the glaciers have retreated more than 1km from 1940. The advances range from 5.4km to 1.1km.
Why have cold environments changed?
Changes in the Earth’s orbit: Changes in the shape of the Earth’s orbit as well as the Earth’s tilt and precession affects the amount of sunlight received on the Earth’s surface. These orbital processes, which function in cycles of around 75,000 years, are thought to be the most significant drivers of ice ages according to the theory of Mulitin Milankovitch.
Changes in the sun’s intensity (picture 14): Changes occurring within the sun can affect the intensity of the sunlight that reaches the Earth’s surface. The intensity of the sunlight can cause either warming (stronger solar intensity) or cooling (weaker solar intensity). According to NASA research, reduced solar activity from the 1400s to the 1700s was likely to be a key factor in the “Little Ice Age” which resulted in a slight cooling of North America, Europe and probably other areas around the globe.
Volcanic eruptions: Volcanoes can affect the climate because they can emit aerosols and carbon dioxide into the atmosphere.
Aerosol emissions: Volcanic aerosols tend to block sunlight and contribute to short term cooling. Aerosols do not produce long-term change because they leave the atmosphere not long after they are emitted. According to the USGS, the eruption of the Tambora Volcano in Indonesia in 1815 lowered global temperatures by as much as 5ºF and historical accounts in New England describe 1816 as “the year without a summer”.
Carbon dioxide emissions: Volcanoes also emit carbon dioxide, which has a warming effect. For about two-thirds of the last 400 million years, geologic evidence suggests CO2 levels and temperatures were considerably higher than present…However, the evidence for this theory is not conclusive and there are alternative explanations for historic CO2 levels.
Current Greenhouse effect: While volcanoes may have raised pre-historic CO2 levels and temperatures, human activities now emit 150 times as much CO2 as volcanoes. This has been a major factor for recent glacial retreats.