Sections written by Laurence Kimpton
What happens at the Poles affects us, and our lifestyles affect the Poles. The International Polar Year aims to highlight some of these connections through the development of websites.
The International Panel on Climate Change report of 2001 produced a map showing the extent of predicted climate change by the end of the 21st century. The map shows that the most northerly parts of the world, the Arctic Ocean and surrounding areas of land, are expected to warm by 6°C or more during this century. This is more than in any other major region of the world and double the global average increase of 3°C. Therefore we can expect that the effects of global warming to be felt very severely in the Arctic.
Some environments in the world are particularly sensitive to all types of change - whether it is changing climate or the impact of peoples' activities. For example, very low lying coastlines are obviously particularly affected by rising sea levels and in warmer regions, they will be particularly badly affected by hurricanes. The Arctic is a very sensitive, delicate environment and slight changes can cause major effects, so even slight climatic change can have a large impact. As global warming is expected to be particularly great in the Arctic its effects are therefore likely to be very severre indeed.
In Antarctic areas, the world map shows that global warming is predicted to be less than in the Arctic (3°c or less by 2100), but because the environment is particularly sensitive to change, the impact of climate change is still likely to be great.
The arrangement of land and sea in the Arctic is almost opposite to that of the Antarctic. The Arctic consists of ocean surrounded by land masses and islands. The central part of the Arctic Ocean, centered on the North Pole, remains frozen throughout the year and in winter almost all the Arctic Ocean freezes. On some parts of the surrounding land there are ice sheets, the Greenland ice sheet being by far the largest.
In contrast, the Antarctic consists of a continental land mass almost entirely covered by an ice sheet surrounded by ocean. Large areas of sea surrounding the Antarctic continent freeze in winter.
Almost every time that a news report on climate change appears on the television news the background pictures show melting ice in the Polar regions, usually an iceberg breaking off (calving from) a glacier into the sea. Every year ice forms from the build up of snow, while at the same time ice melts or is lost from the ice sheets by the calving of icebergs. Global warming has increased the rate of ice loss and so the quantity of ice that is lost from ice sheets is increasingly greater than the quantity which forms from snowfall.
In Polar areas, there are two types of ice: sea ice and the glacial ice of ice sheets. It is very important to understand the difference between these two types of ice when thinking about melting ice in polar areas.
Global warming has meant that summers in Polar areas have become longer and warmer. The sea ice, which forms each winter, therefore melts earlier and so, year by year, more ice melts and the summer extent of sea ice decreases. Some scientists predict that by 2100 summer sea ice in the Arctic will disappear entirely. As far as ice sheets are concerned, longer and warmer summers accelerate melting so that the amount of ice which is lost each year exceeds the amount which forms through the build up of snow. This is especially true with the Greenland ice sheet which is becoming thinner and is losing an increasing amount of ice through calving of icebergs.
Sea ice is frozen sea water and can be up to 3m thick. In Polar areas large areas of sea freeze in early winter and melt in summer. Around the North Pole large areas of sea are permanently frozen. When melting takes place the ice breaks up into large drifting pieces called ice floes. Sea ice does not always have a flat surface - ridges are formed as ice is moved, sometimes against the land, by sea currents and the wind. Ice floes may be pushed together and refrozen to form an irregular surface. As sea ice is formed from the ocean's water, it will not cause sea level to rise when it melts.
The ice sheets of Antarctica, Greenland and Arctic Islands such as Spitzbergen are made up of glacial ice. Snow falls on the land and over long periods of time builds up. As the snow builds up it is compressed by the weight of the snow above and forms ice. In this way ice sheets form. The ice will gradually move outwards form the areas where it accumulates towards the surrounding sea. Much of the outward flow is concentrated into huge outlet glaciers. Where these glaciers reach the sea large pieces break off (or calve) to form icebergs. Over large lengths of the edge of Antarctica large masses of the ice sheet edge float on the sea to form ice shelves. These ice shelves may calve very large tabular (table-like) icebergs. Icebergs of all sizes will drift into warmer waters and gradually melt. Any melting of ice sheets which exceeds the build up of snow will contribute to rising sea levels.
Increased melting of sea ice in summer will not cause sea level to rise because sea ice is already part of the ocean, but the presence of less sea ice in summer will have a number of important effects:
How might these penguins be affected by climate change? Their food supply may decrease (as less sea ice leads to less plankton and therefore less krill for the penguins). They have already been affected by climate change in a rather unexpected way. Increased snowfall from stormier weather has meant that snow-free sites for their nests appear later in the early summer. As a result they lay eggs later and the chicks hatch later, so the chicks may not have grown enough to survive the following winter.
Global warming is already causing sea level to rise slightly, mainly through the thermal expansion of the oceans. As the oceans warm, the water will expand in the only direction it can - upwards. In the future it is likely that the melting of ice sheets will contribute more and more to rising sea level; huge volumes of water contained in ice sheets on land will be transferred to the sea.
The Greenland ice sheet is the most vulnerable to melting; most of it is in the northern polar zone of most rapid global warming. Until recently, the Greenland ice sheet showed a balance between snow building up and the loss of ice through melting and the calving of icebergs. insert diagram of Greenland
Moderate global warming has caused the Greenland ice sheet to thin through melting at the surface and more rapid flow to the edges of the sheet where the icebergs calve. Over the past few years, slightly quicker global warming has caused much more rapid melting and break up of the Greenland ice sheet than scientists had predicted. The ice sheet has continued to thin because of its surface being in contact with warmer air. However, water from melted ice has formed lakes on the surface. This water runs into large cracks or crevasses which carry it to the base of the ice sheet. Once the meltwater reaches the bottom of the ice sheet, it forces its way between the ice and the underlying rock. This makes the ice flow more easily over the rock - the water acts as a lubricant. In Western Greenland, the Jakobshavn Glacier, the largest outlet glacier from the ice sheet, now moves 40m a day, double its rate of flow 20 years ago. As the snouts (ends) of the speeded up glaciers reach the sea, they break up rapidly. interactive link
This unexpected formation of large meltwater lakes on the ice sheets and the resulting more rapid flow of ice towards the sea is an example of how a certain amount of global warming causes an unexpectedly large effect. It is as if a critical ‘tipping point' is reached. This idea of global warming pushing processes along to a tipping point where the effects of climate change are felt more suddenly or even when they are not expected, is a very important idea when looking at the effects of climate change.
In Antarctica the problem of a rapidly melting ice sheet is less severe than in Greenland. The balance between the build up of snow and the loss of ice is more stable. In the Antarctic Peninsula, the mountainous finger pointing towards South America, stormier weather linked to global warming has led to increased snowfall in recent years. However, the West Antarctic ice sheet is less stable and some scientists believe that it will soon follow what is now happening in Greenland. At the edge of the Antarctic ice sheet there are several large ice shelves, something not present in Greenland. Ice shelves are formed where a very wide front of the ice sheet meets the sea, does not melt, but floats out onto the sea. They gradually move forward with the pressure of ice from behind and large tabular icebergs break off. In recent years the warming of the oceans has put a greater strain on the ice shelves, resulting in very large sections breaking off. The largest break up so far has been the Larsson B ice shelf on the east side of the Antarctic Peninsula. The break up and melting of ice shelves does not directly contribute to rising sea levels as they are already floating in the ocean. However, they act as dams to the glaciers behind them on the land; therefore the break up will lead to these glaciers flowing more quickly towards the sea.
Average global warming by 2100 is expected to be 3°C. It is predicted that this will lead to a rise in sea level of between 18 and 59cm. Because global warming is greater in the Arctic and there is evidence that the melting of the Greenland ice sheet is greater than might be expected from even this higher level of warming, some scientists suggest that the rise in sea level will be much greater than 59cm.
Rising sea levels of up to 59cm will have a severe impact on many parts of the world. Especially vulnerable will be the low-lying densely populated coastlands such as the Ganges Delta of Bangladesh, many of the world's coastal cities and low-lying tropical islands. Although the Arctic is very sparsely populated, almost all its settlements are on the coast. Some are already being affected and others will be vulnerable in the future
Most of the land surrounding the Arctic Ocean is a subarctic environment. much of the surface is current with tundra vegetation, a mat of low-growing shrubs, grasses, mosses and lichens. Below the surface layer of soil, the ground is permanently frozen-permafrost. The surface layer is frozen in winter, but thaws in summer; because of the frozen layer below, water cannot drain away easily, so the surface is often boggy and will very slowly move down slopes. Because it easily moved, the surface area is called the active layer.
The tundra areas with underlying permafrost are found in Alaska, northern Canada, areas of Greenland not covered by the ice sheet, northern Scandinavia and northern Russia. As with the High Arctic, these areas are warming more than elsewhere in the world. Already warming is resulting in longer summers; plants are flowering earlier and birds lay their eggs earlier.
The most important effect of global warming in these areas is the melting of permafrost, ground which has remained frozen for thousands of years. Once permafrost begins to melt it is as if the ‘glue' holding the ground together is removed and so the ground becomes unstable. In permafrost areas many buildings are constructed on stilts which pass through the surface active layer and rest on the permafrost. Other buildings rest on concrete platforms underlain by 2m thick gravel pads, so that no thawing will take place underneath them. Roads and aircraft runways also rest on thick gravel pads for stability. If permafrost melts buildings and roads will no longer rest on a solid base and will sink unevenly, tilt or even slip down slopes. Rivers and coastal waves will erode away unfrozen ground much more quickly. permafrost interactive
The melting of permafrost also has a more serious long-term effect. Many areas of permafrost, especially huge areas of Siberia in Russia, consist of frozen organic matter-frozen bogs containing remains of thousands of years plant life. When these frozen bogs melt large quantities of the greenhouse gases carbon dioxide and methane (a product of the decayed vegetation in the bogs) are released into the atmosphere. A molecule of methane is about 20 times as effective as a greenhouse gas than a molecule of carbon dioxide. Therefore the process of global warming is accelerated by the melting of permafrost.
Grise Fiord, on the south coast of Ellesmere Island, is Canada's most northerly Inuit settlement, lying at 76°N. Winter darkness lasts from the end of October to mid-February. Ten years ago the sea was frozen for ten months each year; this period of sea ice has now reduced to almost 9 months. Grise Fiord can be reached be a regular air service or in mid-summer by ship. 135 people, almost all Inuit live here. Hunting for seals, beluga whales (small white whales), narwhal (a small whale with a long tusk), walrus, musk-ox and polar bears is a very important part of their way of life. Most families have someone in ‘modern' employment, for example, in the Co-op store, the school, the community centre, the hotel and the health centre. There is also some income from tourism and visiting scientists.
Look at the pictures of Grise Fiord, all taken in August. How do you think the way of life for Grise Fiord's people will be altered by climate change? Think warmer summers, shorter winters, less sea and, further into the future, rising sea-level.