WASHINGTON -- Booming sound waves halfway around th world, a team of U.S. scientists hopes to resolve one of the hottest scientific debates of the age: Is global warming fact or fantasy?
The team will set sail soon for a volcanic island near the icy fringe of Antarctica to begin a series of underwater tests that, if successful, could develop into one of the most ingenious and closely watched global experiments in history.
The expedition of oceanographers and marine biologists plans to embark on two research ships from the west Australian port of Fremantle on or about Jan. 9 and drop anchor some two weeks later off Heard Island, a remote and uninhabited Australian territory in the south Indian Ocean.
There the scientists will lower a giant loudspeaker into the sea and, for 10 days, transmit intermittent low-frequency signals, which they hope will be audible to highly sensitive listening devices located at 17 or 18 monitoring points around the globe -- some as far as 10,000 miles away on both east and west coasts ofNorth America.
At this stage, the Heard Island experiment is no more than a test to see if sound can be transmitted clearly over vast stretches of ocean. If successful, however, scientists involved with the project say it could develop into an international cooperative effort to prove or disprove that the oceans are growing warmer.
The entire project hinges on the fact that the speed of sound increases with the temperature of the medium through which it travels -- the inference being that any warming of the oceans would cause a slight but measurable shortening of the time it would take for the Heard Island sounds to reach the monitors. The farther sound travels, the easier it is to spot any changes in speed and the more accurately they can be measured; hence the extensive range of the experiment.
As warming would be a gradual process, scientists say it would take at least 10 years to glean reliable data.
The concept is the brainchild of Walter Munk, professor emeritus at Scripps Institution of Oceanography in California. Over the last four decades, he has been the leading pioneer of the relatively young science of tomography, a branch of oceanography that uses sound to map the oceans.
The experiment has fired the imagination of scientists around the world, partly because of what U.S. naval oceanographer Mel Briscoe describes as "the elegant and simple" way it confronts a vastly complex question -- an essential attribute of all great scientific experiments -- and partly because the issue itself is of global concern.
"So much is being said about whether or not there is global warming . . . . Yet nobody has come up yet with a way of measuring it," said Dr. Fred Saalfeld, director of the Navy's Office of Naval Research. "Now, finally, here's a guy who says he may have a way. We've got to give it a try." Naval Research is sharing the estimated $500,000 cost of the experiment with the National Oceanic and Atmospheric Administration, the National Science Foundation and the Department of Energy.
"The Navy is not a disinterested partner in this," Dr. Briscoe said. "Itwouldn't take much warming for sea levels to rise a meter or so, and think what that would mean for all those naval port facilities around the world. . . ."
During a lecture in Washington recently, Professor Munk said that the Heard Island experiment, if successful, would be able to measure anticipated ocean warming of four-thousandths of a degree Celsius a year -- translating to an annual increase of a quarter-second in the underwater speed of sound. This, he said, would represent the most technologically advanced method of measuring oceanic warming.
It would take 200 years to measure ocean warming by simply reading a thermometer, he said. And although orbital satellites would be able to measure minute rises in sea level, which would occur if warming were taking place, they would not be as accurate as underwater acoustics, he said.
While global warming, or the greenhouse effect, is popularly regarded as a fact, it is still not scientifically proven.
Analysis of gas bubbles trapped in polar ice samples over thousands of years, and a variety of other data, show that atmospheric concentrations of fossil-based gases such as carbon dioxide and methane have risen in step with the dramatic industrial development and deforestation of the last 150 years. What remains in dispute, however, is whether these gases are causing the world -- including its oceans -- to become warmer.
PD Enter the Heard Island experiment. Scientists from at least nine
nations are involved in the monitoring, including Australia, Canada, the Soviet Union, India, Japan, South Africa, New Zealand and Brazil, plus representatives from U.S. naval facilities and several private oceanographic institutions. It remains uncertain whether a French group will participate.