But they call home regularly.

"Here's one that just came up today, off Hawaii," the University of Washington oceanographer says, scrolling through a list on his computer. A mouse click reveals another floating under the ice south of Australia.

Riser's babies are torpedo-shaped robots designed to measure ocean temperature, salinity and currents and beam the data back via satellite. Scattered around the globe - indeed, just about everywhere - the probes are part of the first worldwide network to monitor the 70 percent of the planet covered with water.

"We've never had anything like this," says Riser, whose team recently celebrated a milestone: deployment of the 3,000th robotic float.

They set that target nearly a decade ago, part of the team's pitch that scientists need to know what's going on in the oceans in order to understand climate change. Even before the network - called Argo - was complete, it helped refine forecasts of global warming's likely impacts on sea levels and on patterns of drought.

"The Argo floats are creating a revolution in oceanography and our ability to do climate prediction," says Kevin Trenberth, head of climate analysis at the National Center for Atmospheric Research.

"They must be kept going," he says, a reference to the team's fight to ensure that international collaboration doesn't unravel for lack of maintenance money.

"We have 3,000 floats now - but you have to keep replacing them," Riser says. "This is only the beginning."

But it's a good position, considering skeptics said the project would never work.

It's not that anyone doubted the powerful role oceans play in global climate. Warm currents in the Atlantic keep England and northern Europe from being as frigid as the Canadian plains. When the equatorial Pacific heats up, the resulting El Niños can change weather patterns around the world.

As greenhouse gases from cars and power plants trap more heat in the atmosphere, the oceans - which absorb much of that heat - will largely determine which places will get rainier, which will dry out and how storm patterns will shift.

What worried naysayers was the technical difficulty in pulling off the $80 million plan. Ocean monitoring had always been a laborious and costly job, requiring a research ship and crew to maintain the finicky instruments.

It was the development of compact, automated sensors capable of withstanding years of battering in the waves that made Argo possible. The first buoys were deployed in 2000.

At about 5 feet tall and weighing less than 60 pounds, the probes are considerably smaller than the oceangoing marvel for which they were named: The mythical sailing ship that carried Jason and his Argonauts on their quest for the golden fleece.

Each probe is programmed to sink to a depth of more than a mile, then drift in total darkness for nine days - deeper than submarines prowl. Every 10th day, the probes ascend, collecting temperature and salinity measurements as they go. At the surface, they transmit their data, then descend for another cycle.

"This is an entirely new way of observing the oceans," says Dean Roemmich of Scripps Institution of Oceanography in San Diego, a member of the project's steering team.

Whereas data from ships provide only scattered snapshots, Argo buoys - deployed about 180 miles apart - provide regular updates. Riser likens the network to the weather balloons and other meteorological instruments that take the atmosphere's pulse several times a day for weather forecasting.

For the southern hemisphere, a place where few ships travel, the number of deep measurements gathered by Argo exceeds the entire historical record.

All the data are available free on the Internet, where scientists can track individual robots.

Each float costs about $20,000 to build and deploy. To keep the network at its current strength will require about 700 replacements a year, at a cost of $14 million. More than 20 nations have contributed to the project so far, with the United States picking up half the tab.

Steve Piotrowicz, who manages the program for the National Oceanic and Atmospheric Administration, is relying on the "scream factor" to keep the project alive: The more useful Argo becomes, the more people will scream if it goes away.

Already, shippers and seafood fleets are turning to Argo data to help plot currents, routes and promising fishing grounds. More than 1,000 scientific papers have drawn on its measurements.

Argo data also are pointing up weaknesses in the current understanding of climate change. Between 2003 and 2007, for example, Argo floats measured no appreciable warming in the upper oceans - a period when temperatures on land continued to break records. At the same time, sea level has been rising faster than can be explained by melting glaciers alone, says Josh Willis, of NASA's Jet Propulsion Lab.

"The lack of warming over a period of a few years isn't really that surprising, because of all the natural variability," Willis says. "It's a bit of a mystery what's going on with sea level."

Which is all the more reason to make sure Argo keeps running, Trenberth says.

A new generation of robots is already in the works, to gather more information at lower cost.

Riser is tinkering with sensors to gauge the ocean's biological productivity, measure wind speeds and estimate rainfall. Roemmich is shrinking the instruments down.

And the scientists have developed a system any parent would envy: a satellite phone link that will allow them to beam instructions to the robots, instead of having to wait for their creations to call in.