sea levels worldwide have risen an average of nearly 3 inches (8 centimeters) since 1992, the result of warming waters and melting ice, a panel of NASA scientists said Wednesday. In 2013, a United Nations panel predicted sea levels would rise from 1 to 3 feet (0.3 to 0.9 meters) by the end of the century.

The new research shows that the sea-level rise most likely will be at the high end of that range, said University of Colorado geophysicist Steve Nerem.

Sea levels are rising faster than they did 50 years ago and "it's very likely to get worse in the future," Nerem said.

The changes are not uniform. Some areas showed sea levels rising more than 9 inches (25 centimeters) and other regions, such as along the U.S. West Coast, actually falling, according to an analysis of 23 years of satellite data.

Scientists believe ocean currents and natural cycles are temporarily offsetting a sea-level rise in the Pacific, and the U.S. West Coast could see a significant hike in sea levels in the next 20 years.

A rise in global sea levels of more than a meter is unavoidable, scientists say, but they are not sure exactly when, where or how much it will be.

The NASA experts, working with European scientists, say such major cities as Tokyo and Singapore, the U.S. state of Florida, and a number of island nations could disappear.

The scientists say current data suggest a rise in ocean levels of at least 1 meter is a certainty in the next 100 to 200 years. But they say it could be much more depending on rate of loss of the polar ice sheets around Greenland and Antarctica.

They are also unsure when and precisely where the Earth could expect to see such a catastrophic rise in sea levels, saying ocean currents and other natural cycles vary.

According to Tom Wagner, the cryosphere program scientist at NASA, the paleoclimate record shows that sea levels can rise as much as 10 feet (3 meters) in a century or two, if the ice sheets fall apart rapidly.

"We're seeing evidence that the ice sheets are waking up, but we need to understand them better before we can say we're in a new era of rapid ice loss," he said.

Eric Rignot, glaciologist at the University of California-Irvine, said that as the planet warms, there is no reason to expect that ice sheets will melt at the same pace as they did in the past. According to the laws of physics, they will deteriorate faster. And they already are.

"We are not talking about futuristic scenarios," said Rignot.

"On a personal level, the data collected over the past few years make me more concerned about the decay of the ice sheets than I was in the past," he added. "As we go on, I think we are a bit more worried about what is happening."