The nation's ability to track retreating polar ice and shifting patterns of drought, rainfall and other environmental changes is being put "at great risk" by faltering efforts to replace aging satellite-borne sensors, a panel convened by the country's leading scientific advisory group said.
By 2010, the number of operating Earth-observing instruments on NASA satellites, most of which are already past their planned lifetimes, is likely to drop by 40 percent, the National Research Council of the National Academies warned in a report posted on the Internet yesterday at www.nas.edu.
The weakening of these monitoring efforts comes even as many scientists and the Bush administration have been emphasizing their growing importance, both to clarify risks from global warming and natural hazards and to track the condition of forests, fisheries, water and other resources.
Several prominent scientists welcomed the report, saying that while the overall tightening of the federal budget played a role in threatening Earth-observing efforts, a significant contributor was also President Bush's recent call for NASA to focus on manned space missions.
"NASA has a mission ordering that starts with the presidential goals -- first of manned flight to Mars, and second, establishing a permanent base on the Moon, and then third to examine Earth, which puts Earth rather far down on the totem pole," said F. Sherwood Rowland, an atmospheric chemist at the University of California, Irvine, who shared a Nobel Prize for identifying threats to the ozone layer.
In an e-mail statement, John H. Marburger III, President Bush's science adviser and director of the Office of Science and Technology Policy, acknowledged that there were many challenges to maintaining and improving Earth-observing systems, but said the administration was committed to keeping them a "top science priority."
The report, "Earth Science and Applications From Space: National Imperatives for the Next Decade and Beyond," proposed spending roughly $7.5 billion in constant 2006 dollars on new instruments and satellite missions through 2020, saying that would satisfy various scientific and societal priorities while holding annual costs around what they were, as a percentage of the economy, in 2000.
"We're trying to present a balanced, affordable program that spans all the earth sciences," said Richard A. Anthes, the co-chairman of the committee that wrote the report and the new president of the American Meteorological Society.
The report is the latest in a string of findings from such panels pointing to dangers from recent disinvestment in the long-term monitoring of a fast-changing planet.
"This is the most critical time in human history, with the population never before so big and with stresses growing on the Earth," Dr. Anthes said. "We just want to get back to the United States being a leader instead of someone you can't count on."
Satellite-borne instruments, using radar, lasers and other technology, have revolutionized earth and climate science, allowing researchers to accurately and efficiently track parameters like sea level and tiny motions of the Earth from earthquakes, the amount of rain in a cyclone and moisture in air, and the average temperature of various layers of the atmosphere.
The committee identified significant gaps in instrumentation or plans for satellites orbiting over the poles, around the Equator, and positioned so that they remain stationary over spots on the rotating Earth.
One of the most important aspects of such monitoring is launching new satellites before old ones fail. Without this overlap, it is hard to assemble meaningful long-term records that are sufficiently precise to uncover trends, the report's authors said.
The report went beyond discussing ailing hardware and said the White House science policy office should do more to ensure that society and science were benefiting fully from the reams of data flowing from orbiting instruments.
Senior officials at NASA and the National Oceanic and Atmospheric Administration welcomed the report and said it would be considered as they sought to sustain Earth observations in a time of tight budgets.