Ice on Greenland is melting four times faster than it did just 16 years ago, a study reports.

The melting, which is a result of the Earth's warming atmosphere and oceans, is happening much faster than scientists had thought and will likely lead to faster sea-level rise.

"Increasingly, large amounts of ice mass are going to leave as meltwater, as rivers that flow into the sea," said study lead author Michael Bevis of Ohio State University.

A large part of this melting ice is in Greenland's southwestern area, which scientists didn't think was melting so fast. "Southwest Greenland could become a major contributor to sea level rise under continued climate warming," the study said.

The study was published Monday in the peer-reviewed journal Proceedings of the National Academy of Sciences. It is yet another scientific study that reports on the loss of ice in the world's coldest places, including Antarctica.

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Rising seas are especially concerning for coastal U.S. cities, including New York City and Miami, along with vulnerable island nations around the world.

Sea level has risen nearly 8 inches worldwide since 1880, primarily because of global warming, but also because of sinking land in some areas. It's one of the most obvious results of our warming planet, which is heated up by burning fossil fuels such as oil, gas and coal.

Researchers were able to measure the ice loss on Greenland using both instruments on the ground and by poring over data from orbiting satellites.

Though it would likely take centuries, most or all of Greenland’s ice could eventually melt, raising global sea levels 23 feet, Penn State glaciologist Richard Alley told National Geographic.

Lead author Bevis said that once the melting starts in earnest, "there is no turning back."

"The only thing we can do is adapt and mitigate further global warming – it's too late for there to be no effect," he said in a statement. "We are watching the ice sheet hit a tipping point.

"We're going to see faster and faster sea-level rise for the foreseeable future," Bevis concluded. "Once you hit that tipping point, the only question is: 'How severe does it get?'"