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GCOS Terrestrial ECV T6 Introduction:
Changes in mountain glaciers and ice caps provide some of the clearest evidence of climate change, constitute key variables for early-detection strategies in global climate-related observations, and cause serious impacts on the terrestrial water cycle and on societies dependent on glacial melt water. The Global Terrestrial Network for Glaciers (GTN-G), based on century-long world-wide observations, has developed an integrated, multi-level strategy for global observations. The strategy combines detailed process-oriented in situ studies (annual mass balance) with satellite-based coverage of large glacier ensembles in entire mountain systems (glacier inventories, digital elevation models). Satellite Observations: The state of the polar ice sheets and their volumes are both indicators and important parts of climate change processes and feedbacks. Consequently, it is important to monitor and study them in order to investigate the impact of global warming and to forecast future trends. The IPCC expects that, globally, ice sheets will continue to react to climate warming and contribute to sea level rise for thousands of years after the global climate has been stabilised. They note that: — contraction of the Greenland ice sheet is projected to continue to contribute to sea level rise after 2100. Current models suggest virtually complete elimination of the Greenland ice sheet and a resulting contribution to sea level rise of about 7 m if global average warming in excess of 1.9 to 4.69C relative to pre-industrial values was sustained for millennia; — ice dynamic models suggest that melting of the West Antarctic ice sheet could contribute up to 3 m of sea level rise over the next 1000 years, but such results are strongly dependent on model assumptions regarding climate change scenarios, ice dynamics and other factors. Satellite remote sensing allows observations of the changes in the shape of ice sheets, and identification of the shape and size of large icebergs that have detached from the ice sheet. SAR instruments are one source of data on the polar ice sheets. RADARSAT provides routine surveillance of polar regions and has created the first high resolution radar images of Antarctica, enabling detection of changes in the polar ice sheet and improved understanding of the behaviour of the Antarctic glaciers. ASAR on the Envisat mission is continuing the observations of polar ice topography started by the ERS-1 and ERS-2 satellites. Interferometric measurements by PALSAR, together with observations by the AVNIR-2 instrument on JAXA’s ALOS mission, are contributing to understanding the ice sheet mass balance and glacier variation near the South Pole and in Greenland. Altimeters provide useful data on ice sheet topography. While many have high vertical resolution, their limited horizontal resolution means that their observations over smoother, near-horizontal portions of ice sheets are of greatest value. The RA-2 instrument on Envisat is providing improved mapping of ice caps. Given the significance of information on changes in the continental ice sheets, two missions dedicated to their study have been developed: NASA’s ICESat (launched Jan 2003 but with reduced acquisition capabilities due to technical issues) and ESA’s CryoSat-2 (from 2010, following the loss on launch of CryoSat in 2005). CryoSat-2 will provide an instrument for the ice sheet interiors and margins, for sea ice and other topography, with three-mode operation: — conventional pulse-limited operation for the ice sheet interiors (and oceans if desired); — synthetic aperture operation for sea ice; — dual-channel synthetic aperture/interferometric operation for ice sheet margins. ICESat-II is scheduled for launch in 2015. (Satellite Missions) (CEOS EO Handbook - Earth Observation Plans by Measurement) References:
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