What is the cryosphere, and why should we care?

Iceworld melting into Waterworld?

Feature story - 5 December, 2003
The cryosphere is that part of the Earth made of frozen water and soil: Iceworld, if you will. And according to a new study to be published in January, it's a world that is vanishing rapidly, with potentially devastating consequences.

Walrus on ice floe; Greenpeace tour investigating climate change effects, Chukchi Sea, Alaska.

Imagine a world in which 17 million people are fleeing sea-rise in Bangladesh. A world in which villages that rely on glacial melt for their water supplies become ghost towns as the last of the ice disappears. A world in which polar bears are extinct in the wild. A world in which entire seaside economies and livelihoods are wiped out by a rise in sea level that is measured in meters. Now imagine that aspects of this world could be upon us within the lifetimes of children being born today -- and in some scenarios, in our own lifetimes.

It's a chilling vision of a warming world.

"Mass Balance of the Cryosphere" (Cambridge University Press) has been written by a team of 23 scientists and edited by Dr Jonathan Bamber and Dr Anthony Payne of Bristol University. It focuses on two key components of this sensitive environment: land ice, in the form of ice sheets, caps and glaciers, and sea ice. These are important indicators of both short and long-term climate change. The book warns that the cryosphere is far more sensitive to climate change than has been generally accepted, and that we ignore at our peril the dramatic and disturbing trends that have already been observed globally.

Here are a few examples of the findings in the book:

  • The Greenland ice sheet - the biggest ice mass in the Northern Hemisphere - is melting around its margins. Some climate models predict it could lose half its mass in the next 500-1000 years, contributing 3 m to global sea level rise.
  • The amount of Arctic summer sea ice has reduced dramatically in the past 20 years and could disappear completely within an estimated 100 years.
  • Globally mountain and alpine glaciers everywhere are melting, except for a few glaciers in Europe that are not retreating. The rate of retreat is expected to accelerate over the next century.
  • Antarctica - the largest ice mass in the world - presents a more complex picture, although parts of the West Antarctic Ice Sheet and Peninsula ice shelves are in decline.
  • Evidence indicates that some of the changes being seen in the cryosphere are related to the underlying man-made component of global warming.

Who needs ice?

The implications of the decline of the cryosphere are far reaching and go beyond merely losing snow and ice. Increased fresh water influxes from the Arctic could trigger a slow down or diversion of currents of the North Atlantic. What's commonly known as the Gulf Stream is a part of a "conveyor belt" which brings warm water from the Gulf of Mexico to the shores of Europe, circles up to the Arctic, then plunges back into the deep ocean for another cycle. Without its warming effect, North Western Europe would have a climate similar to Greenland. Changes to the North Atlantic currents could impact other sea currents and temperatures around the globe, setting off chain-reaction climate impacts.

As icesheets retreat, snow which once reflected sunlight and heat back into the atmosphere gives way to earth and rock which absorb its heat. As a result, we may well see accelerated warming in the Arctic, and with it accelerated melt. As the ice disappears, habitats for Arctic animals such as polar bears, seals and other large predators are lost.

Depending on how much of the cryosphere is lost, global sea level rise could be measurable in metres. A sea level rise of only 1.5m would displace up to 17 million people in Bangladesh alone.

And beyond the icesheets, glacial retreats in many parts of the world will mean reduced water for human consumption, agriculture and hydro-electricity, shifting economic and social patterns.

Sea Ice

There are warning signs that during the latter half of the 20th Century the Arctic has undergone substantial climate change. One of the key indicators is sea ice extent and thickness, both of which have shown a measurable and disturbing decrease during the last half of the century.

If summer rates of ice decrease continue or accelerate there could, potentially, be no summer sea ice in the Arctic within 100 years or less. This will have major impacts on energy and moisture exchange and consequently on the climate of the Northern Hemisphere, including the risk of altering or slowing down the Gulf Stream.

The consequences of such dramatic changes in sea ice cover are the subject of a number of climate modelling studies and it is, currently, too early to say precisely what the implications of these changes might be. However such changes are likely to include impacts on wildlife and indigenous populations, as well as increasing the positive feedback of higher temperatures as the ice disappears.

There is general agreement that acceleration in melting globally will take place over the next century if greenhouse gas emissions continue to accelerate at the rate they have done for the past 50 to 100 years. Extrapolation of the present trend suggests a reduction in area of the Arctic sea ice of 4.7 million square km by 2100, i.e. virtually complete elimination of the Arctic ice pack in summer. If the predictions of warming in the Arctic over the same time period are taken into account, the rate of melting could be considerably faster as the Arctic is particularly sensitive to temperature increase.


In lower elevations in Greenland, ice sheet loss is conservatively estimated to be 50 cubic km/year, which is equivalent to 0.13 mm/year of sea level rise. As most ice sheet data has been collected only over the past few decades or less, it is difficult to know how long this negative imbalance has existed but it has certainly been enhanced by the warming during the 1990s, and the record melt extent observed in 2002.

The thinning rates cannot be explained by increased surface melting alone, so the implication is that something else is causing this. Extensive thinning in several separate areas suggests that this may be climatically induced, for example, by increased surface melt water reaching the bedrock on which the ice sits, causing the ice to slide on its bed. If true, this is of profound significance as it suggests that the dynamic response time of the ice sheet is, potentially, much shorter than previously believed. Such a rapid dynamic response to changing climate has not, to date, been satisfactorily incorporated in modelling studies, nor have the complex interactions between ice, the oceans, and the atmosphere. All of which means that ice loss could in fact be much faster and greater than currently predicted. This could mean that some of the impacts previously predicted to occur hundreds of years in the future could happen much faster, perhaps within a century.

Antarctic Ice Sheet

While the East Antarctic Ice Sheet appears to be close to balance; it is a different story on the West Antarctic Ice Sheet. There has been a significant warming on the peninsula of about 4 degrees Celsius in the last 50 years, associated with a regional decline in sea ice. While this is a strong signal, it's quite localised. Ice shelves along the Peninsula are only a few hundred metres thick and float on the surface of the ocean and are quite sensitive to changes in the ocean temperature and ocean circulation. Two major ice shelf collapses have been observed over the last decade along the Peninsula.

Glaciers and ice caps

Water stored in glaciers and icecaps around the world would contribute 0.5m sea level rise if they all melted. This is small compared to the 68.3m sea level rise that total melting of the Greenland and Antarctica ice sheets would cause (6m and 62m, respectively). However, glaciers respond much more rapidly than ice sheets. Glacier and ice cap response times are typically below 100 years, which means that the bulk of the cryosphere's contribution to human-induced sea-level rise over the coming century is likely to come from these types of ice mass. There are more than 160,000 glaciers worldwide, making measurement of glacier mass balance very difficult, but existing research indicates that glacial loss is responsible for between 0.22mm to 0.25mm a year sea level rise.

More complex analysis is needed to understand how glaciers react once melting begins, and what a partial loss of glacier ice would mean for its water flow system. The assessment of historical and predicted future contributions to sea level from glaciers is still in its infancy. Changes in ice amounts have clearly been large and are likely to continue to be important over the coming century, however many challenges still remain in their accurate measurement.

Sea ice loss - one example of how this might affect the environment

According to the Third Assessment Report of Intergovernmental Panel on Climate Change (IPCC), a reduction in sea ice will reduce ice edges, which are prime habitat for marine organisms. Habitat loss for some species of seal, walrus, and polar bear results from ice melt, and animals at the top of the food chain - with their low-reproductive rates - are vulnerable to changes in the polar marine food chains. Some animals may be threatened (e.g., walrus, polar bear, and some species of seal), whereas others may flourish (e.g., some species of fish and penguins).

According to Dr Andrew DeRocher of the University of Alberta, who is a world authority on polar bears, if the sea ice habitat continues to deteriorate at current rates, polar bears and their prey, such as ringed and bearded seals, would be unlikely to retain their current population sizes and distribution. At some point, if the loss of sea ice became so severe that all the Arctic sea ice was lost for a substantial part of the year, we may lose polar bears as a wild species.

The whole Arctic marine ecosystem is tied to the presence and dynamics of the sea ice. The main productivity bloom that occurs each spring is exploited by both resident species and migrants, which is tied to the melting of the annual sea ice. Some arctic species travel halfway around the world to exploit the food sources that flourish along the edge of the melting ice. Life along the edge of the melting sea ice is the basis of Arctic marine ecosystems. Removing this dynamic would have profound consequences for all marine life. If the sea ice is drastically reduced or the timing changed, we can expect the loss of many species that are reliant upon this special habitat. It is likely that we will see species expand from southern latitudes to occupy some of these environments but it is impossible to say which ones. It is hard to understand the dynamics of Arctic ecosystems and even harder to predict with any certainty what may happen if the climate changes substantially.

What causes climate change

Climate change is directly linked to our fossil energy consumption. Global warming of the earth is the result of increasing greenhouse gas emissions. The principal cause is carbon dioxide (CO2), which is released when fossil fuels such as coal, oil and gas are burned.

In 2001 the IPCC issued its Third Assessment Report, which found new and stronger evidence that most of the observed warming of the past 50 years is attributable to human activities. It found that about three-quarters of the anthropogenic (human created) emissions of CO2 during the past 20 years are due to fossil fuel burning.

The IPCC also reported that the average global temperature was projected to rise between 1.4 and 5.8 degrees Celsius in the next 100 years. This is a large increase over projections in the Second Assessment Report (1995), which estimated the increase in temperature to be between 1 and 3.5 degrees. In addition, predictions suggest that this warming will be larger in the polar regions, exacerbating the worrying trends already observed. A 2-degree increase would produce substantial damage to or loss of many natural ecosystems, lead to spread of diseases such as malaria and cause substantial damage to agriculture in developing countries.


Scientific understanding of the Earth's climate and how humans are affecting it is constantly improving, but there is still much to learn about what climate change will mean to natural systems such as the cryosphere. For most people polar regions are remote places that are out of sight and perhaps out of mind. They are, however, highly sensitive to climate change with strong feedbacks at play. Dramatic and disturbing trends have already been observed in the Arctic, Greenland, the Antarctic Peninsula and in glaciers globally.

Risk of sea level rise that could displace millions of people; radical alterations of ocean currents that in turn affect regional climate; loss of glaciers that provide water people need to live; changes to the food chain and even possible dramatic and rapid irreversible changes to the global climate - these are some of the possible impacts of climate change.

The Kyoto Protocol is the one global mechanism to address climate change. As the latest round of Kyoto talks get underway in Milan in December 2003, evidence about the serious impact of climate change is mounting. Governments and industry must take action to protect the climate now and stop trying to weaken the Protocol. It is not only the cryosphere at risk, but also potentially the global climate system.

More Information

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