Lasers From Space Show Thinning Of Greenland And Antarctic Ice Sheets
New comprehensive maps of Greenland and Antarctica show extent of glacier thinning. (Credit: ICESat, NASA)
The most comprehensive picture of the rapidly thinning glaciers along the coastline of both the Antarctic and Greenland ice sheets has been created using satellite lasers. The findings are an important step forward in the quest to make more accurate predictions for future sea level rise.
Reporting last week in the journal Nature, researchers from British Antarctic Survey and the University of Bristol describe how analysis of millions of NASA satellite measurements from both of these vast ice sheets shows that the most profound ice loss is a result of glaciers speeding up where they flow into the sea.
The authors conclude that this ‘dynamic thinning’ of glaciers now reaches all latitudes in Greenland, has intensified on key Antarctic coastlines, is penetrating far into the ice sheets’ interior and is spreading as ice shelves thin by ocean-driven melt. Ice shelf collapse has triggered particularly strong thinning that has endured for decades.
Lead author Dr Hamish Pritchard from British Antarctic Survey says, “We were surprised to see such a strong pattern of thinning glaciers across such large areas of coastline – it’s widespread and in some cases thinning extends hundreds of kilometres inland. We think that warm ocean currents reaching the coast and melting the glacier front is the most likely cause of faster glacier flow. This kind of ice loss is so poorly understood that it remains the most unpredictable part of future sea level rise.”
The scientists compared the rates of change in elevation of both fast-flowing and slow-flowing ice. In Greenland for example they studied 111 fast-moving glaciers and found 81 thinning at rates twice that of slow-flowing ice at the same altitude. They found that ice loss from many glaciers in both Antarctica and Greenland is greater than the rate of snowfall further inland.
In Antarctica some of the fastest thinning glaciers are in West Antarctica (Amundsen Sea Embayment) where Pine Island Glacier and neighbouring Smith and Thwaites Glacier are thinning by up to 9 metres per year.
Keeping An Eye On The Oceans
Jason 2 satellite, operated by EUMETSAT, whose onboard altimeter scans the world’s oceans, recording global sea level to the nearest cm. (Credit: Image courtesy of EUMETSAT)
During the last ten years, scientists have set up a global observing system to monitor the world’s oceans. The observation system works by combining satellite observations with data from in-water recording devices such as buoys, tide gauges and an array of more than 3000 Argo robots.
Scientists met last week at OceanObs’09 in Venice to see how they can expand the system and, perhaps most importantly, secure it for the long term. OceanObs ‘09 was organized by UNESCO’s Intergovernmental Oceanographic Commission and the European Space Agency (ESA) and was attended by EUMETSAT(European Organisation for the Exploitation of Meteorological Satellites) and over 580 participants from 36 countries. EUMETSAT’s role in ocean observations is to establish, maintain and use systems of operational meteorological satellites, contribute to the operational monitoring of the climate and the oceans – for instance monitoring sea level rise with the Jason 2 altimetry satellite – and establish new ocean-monitoring missions, such as Jason 3.
So how does the ocean observing system operate?
In the water, recording devices such as tide gauges, mooring buoys, and drifting buoys, monitor aspects of the sea such as tides, water temperature, and currents. Over the last 10 years, scientists have also dropped more than 3000 Argo robots into the sea, and these robots are now methodically rising and falling around the world’s oceans recording temperature and salinity profiles, and transmitting this data via satellite back to scientists every ten days. The Argo robots are also joined by pilot-less ocean gliders which bristle with recording instruments and soar and glide through the oceans – sometimes down to depths of 6 km – collecting data.
Joining the gliders, scientists have also sporadically enlisted the help of marine animals, such as elephant seals, by attaching miniature data loggers to record the temperature, salinity and depth conditions they experience on their daily travels. And even ships and ferries are playing a part in monitoring the ocean, as boats on regular passage around the world tow plankton recorders interfaced to sophisticated on-board systems, which are like mini oceanographic laboratories.
All this data from the in-water samplers – so called in situ data – provides the detail on conditions in specific locations, but for the big picture of what is happening in the oceans, scientists are relying on satellites. One of the key tools in understanding issues such as global sea level rise is the Jason 2 satellite, operated by EUMETSAT, whose onboard altimeter scans the world’s oceans, recording global sea level to the nearest cm. When this information is combined with information from satellite-based gravity measurements, tide gauges, Argo floats and other devices, it gives scientists the ability to precisely monitor global sea levels. Satellites are also monitoring a host of other ocean variables – from sea surface temperature, to wind, ocean colour and sea ice cover.
One of the most important features of any ocean observing system is that it must be a long-term system if changes are to be understood in the right context. As an example, satellite monitoring of sea levels began in 1992 with the launch of the TOPEX/Poseidon satellite, which was followed by Jason 1 (2001), Envisat (2002) and more recently Jason 2 (2008), which will be joined in 2012 by Sentinel-3, another satellite carrying altimetry equipment.
Dr Hans Bonekamp, Ocean Mission Scientist at EUMETSAT said: “The long-term datasets on sea levels that the satellite altimeters are collecting are enabling scientists to establish how sea levels have changed in the last two decades and understand the effects of global warming at regional and global levels.”
Making sure the existing ocean observation system, both satellite and in situ data, is sustainable in the long-term is one of the key aims of Oceanobs’09, where the ocean observing community will take stock of progress to date and map out the priorities for the next decade – a task that is unlikely to be easy in the current financial climate.
But the benefits that an operational ocean observing system will bring, are an extremely strong justification: the system is already providing data for the International Panel on Climate Change assessments, and it will also provide better data for maritime security, oil spill prevention, management of marine resources, marine meteorology, seasonal and long term weather forecasting, coastal activities, and monitoring of water quality.
