Satellites Let Scientists View Earth as Integrated System Contributor: Cheryl Pellerin, America.gov Staff Writer
Direct observations of oceans, land surfaces, the atmosphere and glaciers have made it possible in 2007 for scientists to state with more than 90 percent certainty that Earth's climate is warming and human activities are driving the change.
Such observations  -  produced by a range of globally networked instruments and individual data collectors  -  have come a long way since the 1600s, when a group of Venetian scientists developed the first thermometer and soon after people began recording the weather.
The first meteorological network formed in northern Italy in 1653. By the last half of the 19th century, people in nearly all inhabited areas of the world were making systematic weather observations, according to the U.N. Intergovernmental Panel on Climate Change's (IPCC) fourth assessment report, Climate Change 2007.
But it was spacefaring, and especially the placement of satellites in orbit around the planet, that helped scientists begin to integrate the complex interactions among Earth's systems of land, air, water and life. (See related article).
Satellites are "indispensable" to Earth observations, Michael King, Earth Observing System senior project scientist at NASA's Goddard Space Flight Center, told USINFO. He called them "the best means of observing the global integrated system without impact on national boundaries or different observing systems."
REMOTE OBSERVATIONS
Remote sensing is defined as collecting information about an object without being in physical contact with the object. Satellites are common platforms for remote-sensing observations and have been used for that purpose since the early days of space flight.
In 1972, the first civil satellite was launched to collect data about Earth. The Earth Resources Technology Satellite, later renamed Landsat 1, developed by NASA, made satellite imagery available to the public for the first time. Since then, a series of Landsat satellites has orbited Earth.
Landsat 5 launched in 1984 and, despite a design life of three years to five years, is still operating, but with limited capability. Landsat 7 launched in 1999, and since 2003 has had a sensor problem that limits its capability. Both satellites will run out of fuel in 2010 or 2011. The next satellite, the Landsat Data Continuity Mission, is expected to launch in 2011.
In the meantime, the United States, European nations, Japan, China and India have launched earth-observing and meteorological satellites.
In the United States, King said, "NASA's Earth Observing System [EOS] was conceived in the late 1980s to be a 15-year term of global Earth observations in Earth system science that would consist of the necessary properties of the planet," including the atmosphere, land, oceans, cryosphere (ice-bound regions) and the driving force of the sun.
EOS consists of a series of satellites, a science component and a data system that supports a coordinated series of satellites in three kinds of orbits. Many satellites carry instruments developed by scientists in Canada, France, Brazil, Russia and Japan. The satellites include:
• Terra (launched 1999), which carries five sensors  -  including sensors from Canada and Japan  -  that study the interactions among the Earth's atmosphere, lands, oceans and radiant energy (heat and light);
• Aqua (launched 2002), a joint project of the United States, Japan and Brazil that carries six sensors to observe Earth oceans, atmosphere, land, ice and snow cover and vegetation; and
• Jason-1 (launched 2001), a joint oceanography mission of NASA and the French Centre National d'Etudes Spatiales that monitors global climate interactions between sea and atmosphere.
EOS data play a major role in the climate assessment reports produced every five years or so by the IPCC, King said, and it is freely available and widely used by people and nations worldwide, "giving people unprecedented views of our ever-changing planet."
OBSERVATION SHORTCOMINGS
Even with advancements in Earth-observation technology, each kind of observation  -  from weather balloons, satellites, ships, weather stations and ocean buoys  -  has its own shortcomings when used as part of the global climate record.
"Most observations, especially in the atmosphere, are made for purposes of weather and weather forecasting, not for climate purposes," Kevin Trenberth, head of the Climate Analysis Section at the National Center for Atmospheric Research, told USINFO.
"They don't have the quality we would like to see for climate," added Trenberth, who was a coordinating leading author of Chapter 3  -  Observations: Surface and Atmospheric Climate Change  -  of the IPCC's Climate Change 2007 assessment report. He also chairs the U.N. World Climate Research Program (WCRP) Observations and Assimilation Panel.
"With a little more care, we always say, [observations] could be much more useful for climate purposes," he added. "In the meantime, there are many workers around the world who heroically try to work with these data to construct the climate record."
The WCRP panel has been lobbying world space and satellite agencies about fixing the observational shortcomings. Its members are proposing to initiate a systematic international program to reprocess satellite data collected since 1970 "to get a better and more continuous view of how things have changed," Trenberth said.
Despite the observational uncertainties, though, scientists remain convinced the Earth's climate is changing and human activities are responsible.
"What it means is that the signal of human influence has become so strong that it overwhelms all the uncertainties," Trenberth said. "In addition, it's not just one piece of information, it's a whole raft of information across a whole lot of different measurements that led to the statement that global warming is unequivocal."
+ NASA's Earth Observatory is available on the agency's Web site.
+ National Center for Atmospheric Research[external site]
+ Climate Change 2007 on IPCC Web site. [external site]
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