Satellite for tracking sea levels set for launch

Jean-Louis Santini, Yahoo News 19 Jun 08;

The French-US satellite Jason 2, slated for lift-off Friday from California, will provide precise monitoring of rising sea levels and currents and track the effects of climate change.

Weather permitting, the high-tech oceanography space lab will be launched aboard a Delta 2 rocket from Vandenberg Air Force Base from 1946 GMT, when a nine-minute window of opportunity for the launch opens.

Fifty-five minutes after take-off, it will reach its orbit some 1,335 kilometers (830 miles) above the Earth.

"We are set to fly," NASA launch manager Omar Baez said on the Spaceflight Now website.

Jason 2 is programmed to maneuver into the same orbit as its predecessor Jason 1, which was launched in 2001, and eventually replace the older craft.

Rising sea levels is one of the most serious consequences of global warming, threatening dozens of island nations and massively populated delta regions, especially in Asia and Africa.

Data from previous missions showed that sea levels have risen on average by 0.3 centimeters per year since 1993, or twice as much as they did in the whole of the 20th century, according to marine measurements.

But 15 years of data is not enough to draw accurate long-term conclusions, say scientists.

The three-year OSTM (Ocean Surface Topography Mission)/Jason 2 mission will help create the first multi-decade global record of the role of the ocean in climate change, according to scientists at NASA's Jet Propulsion Laboratory in Pasadena, California.

It will also provide more accurate forecasts of seasonal weather patterns, and near real-time data on ocean conditions.

"Without this data record, we would have no basis for evaluating change," said the mission's project scientist, Lee-Lueng Fu, in a statement.

Fu compared the sea level record begun in 1992 with the continuous measurements of atmospheric carbon dioxide initiated in the 1950s at the Mauna Loa Observatory in Hawaii.

"The Mauna Loa data proved that carbon dioxide levels were indeed rising as had been predicted, and they were the basis for our understanding of the greenhouse effect," Fu said.

"The height of the ocean is another fundamental measurement of our climate. The key is to have rigorous, well-calibrated data collected over a long period of time."

Global sea levels are expected to rise in the coming years as the Earth warms, scientists have said.

The oceans act as the planet's thermostat, and absorb more than 80 percent of the heat from global warming, with the rest absorbed by the atmosphere, land and glaciers, NASA scientists have found.

Warming water and melting ice are the two main factors contributing to rising sea levels.

The OSTM/Jason 2 mission is a partnership between NASA, the National Oceanic and Atmospheric Administration, the French National Center of Space Studies (CNES) and the European satellite agency EUMETSAT.

Jason 2's most powerful onboard instrument is CNES's Poseidon 3 radar altimeter, which can measure the height of ocean surfaces in relation to Earth's centre with a margin of error of 3.3 centimetres (1.3 inches).

GLOBAL WARMING
Eye-in-the-sky to keep tabs on sea level
Michael Richardson, Straits Times 20 Jun 08;

SCIENTISTS and other specialists who study global warming are eagerly awaiting the launch of a satellite today that will measure the rise of the world's sea level more accurately than ever before.

If the Jason-2 satellite and its advanced radar altimeter are successfully lofted into orbit from a base in California, they will map almost all of the world's ice-free oceans every 10 days for at least the next five years, reducing the margin of uncertainty to within 2.5cm.

The satellite is part of a joint space venture between European and United States space and weather agencies. The information it beams back from nearly 1,340km above the Earth's surface will shed more light on one of the most controversial areas of climate change - the extent to which the sea level will rise in future.

The issue is of critical importance to Asia. With more than four billion people, it is the world's most populous continent. Nearly 40 per cent of Asians live within 100km of a coast, many in low-lying deltas. These include the Yangtze and Pearl river deltas in China, the Mekong in Vietnam, the Ganges-Brahmaputra in Bangladesh, the Chao Phraya in Thailand and the Irrawaddy in Myanmar, which was ravaged by a cyclone last month.

The United Nations Environment Programme has estimated that 100 million people in the great Asian deltas could be displaced by a sea level rise of more than 1m.

Summarising available scientific evidence on global warming, the UN Intergovernmental Panel on Climate Change (IPCC) last year forecast sea level rises ranging from 18cm to 59cm this century, after an increase of 17cm in the 20th century.

The IPCC suggested that most of the projected rise by 2100 would be the result of water in the oceans expanding as it warmed, with little being added by the discharge of water from the melting of the ice sheets that cover Greenland and Antarctica.

But some scientists point to recent signs that vulnerable parts of these two vast ice sheets are melting at an alarmingly fast rate. They warn that this indicates that sea level rise this century could be several metres, rather than the maximum of 0.6m predicted by the IPCC.

If the unstable sections of the Greenland and Antarctic ice sheets were to melt completely, sea levels around the world could rise by 10m to 12m.

Dr Eric Rignot, a scientist working for Nasa, the US space agency, believes that unchecked warming in the 21st century could result in a metre of global sea level rise from water flowing off Greenland, a metre from Antarctica and half a metre as the remaining alpine glaciers melt.

The IPCC report said that coastal zones, especially the densely populated mega-delta regions of South, South-east and North-east Asia, would be at greatest risk due to increased flooding from rising sea levels and storm surges.

Some of these deltas will also be at risk of flooding from overflowing rivers. Mountain glaciers in the Himalayas and the Qinghai-Tibetan plateau may shrivel away, unleashing too much water at first - and then too little for the hundreds of millions of people who depend on their flow.

'The crux of the problem is that we are moving into an era where we are observing changes in the climate system that have never before been seen in human history,' says Dr Gerald Meehl, a scientist at the US National Centre for Atmospheric Research and a coordinating lead author of the latest IPCC report.

'Ice sheets fall into that category. Quite simply, at this time we don't have a good upper-range estimate of how much the sea level will rise and how fast.'

Having the Jason-2 satellite aloft should help. Variations in the height of the sea surface, when combined with measurements from other satellites and tidal gauges at sea level in various parts of the world, will improve weather and climate system models. Whether this will prompt the IPCC to predict a much higher sea level by 2100 than it did last year remains to be seen.

There appear to be some contrary factors at work. For example, warmer air can absorb more moisture and may, paradoxically, bring more snow to Greenland and Antarctica, thus thickening and stabilising the cores of the ice sheets, despite some peripheral melting.

There is also more to the dynamics of sea level rise than just a single, global rise, explains Mr Mikael Rattenborg, director of operations for the European Organisation for the Exploitation of Meteorological Satellites, one of the agencies supporting the Jason-2 launch.

'Although we have seen, overall, global sea level rise, there are areas that have decreased for long periods, followed by an increase,' he says.

'We can only analyse the significance of regional variability of sea level rise if we have altimetry data. Jason-2 will help us model and explain this evolution.'

The writer is an energy and security specialist at the Institute of Southeast Asian Studies.