Greenhouse gases are warming our oceans, changing their chemistry and threatening rainfall patterns that provide the planet with its fresh water, scientists say.

The gases that cause global warming sometimes are given as factors in problems ranging from the strength of hurricanes to altered wildlife habitats. But in what may be the most comprehensive look yet at the oceans, a group of researchers recently told a scientific conference that the marine effect is just as severe.

"In terms of global warming, the oceans are where the action is," said Tim Barnett, an oceanographer at the Scripps Oceanographic Institution. "The oceans are sort of a canary in the coal mine."

The 1990s turned out to be the warmest decade in the past 1,000 years, experts say.

Researchers have studied ocean warming for decades. But their efforts have gained momentum in recent years with improvements in their equipment.

Scientists worldwide have expanded their network of ocean detectors, dropping sensitive probes in seas where they sink up to 6,000 feet and rise automatically to transmit by satellite the temperatures, salt content and oxygen levels at various depths.

The first of 1,600 such profiling floats began collecting data a few years ago as part of an international effort to probe changing conditions, said Sydney Levitus, director of the National Oceanic and Atmospheric Administration's ocean-climate laboratory.

Research and merchant ships also collect data. But the floating detectors — about half of them maintained by the United States — provide a steady stream of reliable data that arrives every 10 days.

"We're getting data in areas where the ships just don't go, places like the Labrador Sea in winter or off South America," Levitus said.

Researchers say the detectors are confirming what computer models long have predicted: Man-made greenhouse gases are warming the seas.

A group of researchers presented findings last month at the American Association for the Advancement of Science conference in Washington, D.C.

Heat trapped

Greenhouse gases, such as carbon dioxide emitted from power plants and automobiles, are trapping heat in the atmosphere, experts say. The result is a warmer planet, with melting glaciers and Arctic ice sheets sending an unprecedented flow of fresh water into fragile saltwater habitats.

The upper two miles of the oceans have warmed by about 0.11 degree Fahrenheit since the 1950s and a total of 1.2 degrees in the past 100 years, according to NOAA.

The Intergovernmental Panel on Climate Change, an international group of scientists, has projected that sea levels will rise up to about 3 feet by 2100.

Since 1965, a volume of water equivalent to the Great Lakes has melted in polar regions and flowed into the world's oceans, making them less salty, said Ruth Curry, a researcher at the Woods Hole Oceanographic Institution.

Meanwhile, in tropical oceans, warmer temperatures are increasing evaporation rates, making them saltier, she said.

An increase in tropical evaporation also could alter the natural cycle of rainfall and evaporation that supplies fresh water and brings warm air into the Northern Hemisphere, she said.

In a feature peculiar to the North Atlantic, cold, salty surface waters sink to deeper levels, driving a system called the Ocean Conveyor. It draws warm Gulf Stream waters northward in the Atlantic, moderating winter temperatures in the Northern Hemisphere.

Concentration of salt

Meanwhile, evaporation concentrates salt in the tropical Atlantic. If global warming accelerates that process, scientists say, the tropical Atlantic may become too salty and the Ocean Conveyor could slow. That, in turn, could bring droughts and much colder temperatures to northern areas.

"It has the potential to affect not only fish and a lot of other kinds of marine life but the ecological systems that depend on them for survival," Curry said.

In his study, Barnett compared temperature and salinity measurements over the past 40 years to estimates made by computer models that factored in human-induced carbon-dioxide levels.

The results show that greenhouse gases created by humans are a major factor in warming the oceans, he said.

"Frankly, it was scary," Barnett told a group at the science conference.

Scientists long have complained that the Bush administration has ignored global warming by arguing that there is insufficient evidence to show that it's caused by humans.

Barnett said the time for arguments has ended. The problem of global warming requires a scientific approach similar to the Manhattan Project, which developed the atomic bomb in World War II, he said.

"The culprit responsible for warming has been identified," he said. "As far as I'm concerned, the debate's over. What we need to be debating is what we're going to do about it."

Robert Hopkins, a spokesman for the White House Office of Science and Technology Policy, said the administration spent $5 billion last year on climate-change research.

He said the government also plans to reduce greenhouse-gas emissions by 18 percent over the next decade and work with the United Nations to find ways to reduce worldwide emissions.

Richard Feely, a researcher for the NOAA, said coral reefs in tropical seas already are being damaged.

He said higher levels of carbon dioxide are forming carbonic acid in seawater that interferes with the production of coral reefs, an integral part of the marine food chain. Exactly which species of corals are most vulnerable remains unknown, he said.

"Certain species seem to adapt, and others don't," Feely said. But he added: "There's no winners in this."