August 31st, 2007 02:10 EST
Observations of Atmosphere, Oceans Quantify Climate Change
This is the second in a series of articles about U.S. contributions to direct observations of the changing climate.
Washington -- World leaders, scientists, environmental groups and industry leaders are gearing up for major international climate change talks -- a September meeting in Washington on global warming, and a December U.N. conference in Bali -- prompted by increasingly dire indications that human activities are changing the planet.
The measurements that tell scientists of rising oceans, melting glaciers and warming air temperatures come from a range of observation networks that crisscross the planet, sampling air and water and transmitting data to scientists around the globe.
Publications like the climate assessment reports produced every five years or so by the U.N. Intergovernmental Panel on Climate Change (IPCC) integrate and analyze such measurements to give a comprehensive view of the current understanding of climate science.
In introducing the first section – the Physical Science Basis – of the fourth and latest assessment report, Climate Change 2007, IPCC Chairman Rajendra Pachauri cited the progress of climate science.
“The extent of knowledge, the research that has been carried out and that has helped us in the preparation of this report,” he said during a February briefing, “is several steps beyond what was possible with the third assessment report.”
VOLUNTEER SHIPS, OCEAN BUOYS
For ocean temperatures, said Thomas Peterson, a research meteorologist at the National Oceanic and Atmospheric Administration’s (NOAA) National Climatic Data Center (NCDC) in North Carolina, scientists rely mainly on direct observations -- from volunteer ships since at least the 1800s and from moored and drifting ocean buoys -- for the long-term record.
“Historically,” said Peterson, also a lead author of the fourth IPCC report’s Historical Overview of Climate Change Science, “ships would throw a bucket overboard, bring it up and stick a thermometer in it. Then [mainly in the 1940s], ships started collecting temperatures at engine intakes. Now, we have ocean buoys, and a whole suite of volunteer ships travel around the world in shipping lanes collecting data.”
A special effort -- the Voluntary Observing Ship Climate Project -- is under way to put out high-quality ship observations, he added. “Special sensors are put on hulls where they take more accurate readings that allow for a different and improved assessment.”
Other ocean observations come from moored buoys, which NOAA’s National Data Buoy Center Web site calls “the weather sentinels of the sea.” The buoys are deployed in coastal and offshore waters from the western Atlantic to the Pacific Ocean around Hawaii, and from the Bering Sea to the South Pacific.
The buoys measure and transmit barometric pressure; wind direction, speed and gust; air and sea temperatures; and wave energy data. They are used in operational forecasting, warnings, atmospheric models, scientific and research programs and other applications.
TAO/TRITON is an array of 70 moored buoys in the tropical Pacific Ocean that transmit oceanographic and weather data to shore in real-time via the ARGOS satellite system, administered by NOAA and France’s Centre National d’Etudes Spatiales. Japan’s Agency for Marine-Earth Science and Technology and France’s Institut de recherche pour le developpement also are involved.
Since 2002, new measurements have come from an international collaboration called Argo, a global array of 3,000 free-drifting floats that measure temperature and salinity of the ocean’s upper 2,000 meters.
At 10-day intervals, the floats pump fluid into an external bladder and rise from 2,000 meters to the surface over a six-hour period while taking measurements. Satellites determine the floats’ positions when they surface and receive their transmitted data. The bladder then deflates and the float sinks to drift until the cycle repeats.
Kevin Trenberth, head of the Climate Analysis Section at the National Center for Atmospheric Research, told USINFO that Argo “is producing a revolution in oceanography that is enormously valuable for determining just what’s happening in the ocean.”
Twice a day, all over the world, at midnight and midday (universal time), 600 to 700 weather balloons, or radiosondes, are launched skyward, eventually to reach 20 kilometers or more, carrying instruments that measure temperature and moisture and radio-transmitting equipment.
Radiosondes have been used to collect global data since the International Geophysical Year in 1958, Peter Thorne, climate research scientist at the Met (for meteorology) Office Hadley Centre in Exeter, United Kingdom, told USINFO, but “the instrumentation over that period has changed beyond recognition.”
Weather balloons, he added, have “been used primarily from a weather forecast perspective. They provide a snapshot of atmospheric characteristics necessary to run global [weather] forecast models.”
Before the 1970s, when weather satellites began to be launched, upper-air data were scarce because very few radiosondes were launched in the tropics or the Southern Hemisphere. Such launches were limited due to economic reasons and because there is more land from which to launch balloons in the Northern Hemisphere.
Today, satellites and radiosondes are the two primary instruments for measuring the upper air.
“A fundamental requirement in my view of a climate-adequate monitoring system is being able to monitor the same variable in more than one way,” Thorne said. “The more ways you monitor variables -- atmospheric, oceanic, any kind of relevant variable -- the better your knowledge is going to be.”
More information about the National Climatic Data Center is available at the NOAA Web site. More information about the IPCC assessment reports and Argo is available at those organizations’ Web sites.
(USINFO is produced by the Bureau of International Information Programs, U.S. Department of State. Web site: http://usinfo.state.gov)
By Cheryl Pellerin
USINFO Staff Writer