Almost 80% of the Earth's fresh water is locked up in the cryosphere, i.e. snow, ice and permafrost. The cryosphere plays an important role in moderating the global climate – and as such, the consequences of receding ice cover due to global warming are far reaching and complex.
Due to its high albedo, ice masses directly affect the global
energy budget by reflecting about 80% of incident sunlight back out
to space. Thus, once formed, ice tends to be maintained. However,
if ice cover were to decrease, less solar radiation would be
reflected away from the surface of the Earth – causing the
ice to absorb more heat and consequently melt faster still.
Around the North Pole, an area of sea ice the size of Europe melts away every summer and then freezes again during the winter. The thickness of Arctic sea ice plays a central role in polar climate as it moderates heat exchange by insulating the ocean from the cold polar atmosphere.
A decrease in sea ice could disturb ocean circulation in patterns in the North Atlantic As sea ice forms, the salinity and therefore the density of the upper ocean increase. The density increase causes the surface waters to sink – in essence acting as a pump, driving cold, deep ocean currents from the polar regions towards the Equator. A reduction in Arctic sea ice could significantly disrupt the Gulf Stream which transports warm surface waters northwards from the Gulf of Mexico to the sub-polar waters east of Greenland. It is thanks to the Gulf Stream that north-west Europe currently enjoys annual temperatures of about 9° C higher than average for the latitude.
As well as influencing how much sunlight is reflected back to space, continental ice has an impact on sea level. The large ice sheets covering Antarctica and Greenland amount to about 28 million km3, which means that sea level is about 65 m lower than it would be if these ice sheets didn't exist. Whilst evidence suggests that these ice sheets are relatively stable, there are indications that rapid changes are occurring around their margins.
CryoSat-2's icy mission is dedicated to monitoring very precise changes in the elevation and thickness of polar ice sheets and floating sea ice over a 3-year period. The observations that CryoSat-2 makes will determine whether or not our ice masses are thinning due to global warming.
Sea ice typically covers up to 15 million square kilometres of the Arctic Ocean, and up to 19 million square kilometres of the Southern Ocean around Antarctica, during their respective winter seasons. This seasonal cycle of sea ice is one of the most dynamic components of the Earth's climate system.
Regional sea-ice models have been successfully developed over the last decades. However, given the impact that sea ice has on the climate, it is essential to acquire more comprehensive data on sea ice thickness to improve sea ice models for their implementation in general climate studies.
To further our understanding of the impact that sea ice has on
climate and to ascertain whether there is currently a trend towards
reduced sea ice cover, CryoSat-2 will provide new and authoritative
data on fluctuations in Arctic and Antarctic sea ice.
An obvious source for this extra water is from the melting of ice sheets and glaciers overlying land. The ice sheets that blanket Antarctica and Greenland are up to around four kilometres thick, and it is the melting of these large ice masses that have the potential to cause a significant rise in global sea level.
The improvement in resolution of the CryoSat-2 radar over that of its pulse-limited predecessors, coupled with its interferometric capability, will make spatially and temporally continuous measurements of the ice-sheet margins and smaller ice masses possible for the first time.
Sea-ice thickness plays a central role in climate processes. Ice extent and thickness have important stabilising effects on world climate, insulating large areas of the oceans from solar radiation in the summer and preventing heat loss to the atmosphere in the winter.
Arbitrary flux corrections in these models, which essentially hold the sea surface temperature at freezing in regions where there is sea ice, make the calculation of the effect of 'perturbations' such as CO2 –induced warming questionable (Gates et al, 1996).
The physics of sea ice in global climate models is, at the moment, oversimplified. With the recognition that variations in thermohaline circulation may have important consequences for poleward-bound heat transport – the next years will see more complete sea-ice physics within global ocean-atmosphere models. These developments demand more information on sea-ice extent and volume changes – which will be provided by the CryoSat-2 mission.
Related (Key) Documentation
Related Software Tools