It is not the warming of the oceans that will likely be the culprit behind rising sea levels, but the slow melting of the ice sheets.

The melting of ice sheets contributed more to the rise in sea levels around the world than the warming of the oceans during the Last Interglacial Period, according to a new study out of the University of Arizona.

The results of the study indicate that the current melting of the ice shelves is a significant threat to coasts across the globe, as sea levels are expected to rise by three feet by the end of the 21st century.

To determine the rate of rising, the researchers analyzed paleoceanic records of sea surface temperatures around the world during the 5,000-year period during the Last Interglacial Period, an era of warmth that lasted from 130,000 to 120,000 years ago.

This data was then compared to computer models simulating ocean temperatures and calculated the contributions from the thermal expansion of water.

They found that the thermal expansion of water could have added no more 1.3 feet in sea levels during that time.

The same data showed that water temperatures during the Last Interglacial Period were only 1.3 degrees Fahrenheit above temperatures today.

"This means that even small amounts of warming may have committed us to more ice sheet melting than we previously thought. The temperature during that time of high sea levels wasn't that much warmer than it is today," said Nicholas McKay, a doctoral student at the University of Arizona's department of geosciences and the paper's lead author.

“Even if we stopped greenhouse gas emissions right now, the Earth would keep warming, the oceans would keep warming, the ice sheets would keep shrinking, and sea levels would keep rising for a long time," he stated in a news release about the study.

The authors imply that 13.5 to 19 feet of sea level increase during the Last Interglacial came from the Antarctic Ice Sheet, "reemphasizing the concern that both the Antarctic and Greenland Ice Sheets may be more sensitive to warming temperatures than widely thought," said Jonathan Overpeck, co-director of the UA's Institute of the Environment and a co-author of the study.

The study cautioned that past evidence is not a prediction for the future, and that different conditions affected the warming of the Earth now compared to the Last Interglacial Period.

"The message is that the last time glaciers and ice sheets melted, sea levels rose by more than eight meters. Much of the world's population lives relatively close to sea level. This is going to have huge impacts, especially on poor countries," McKay said.

The study will appear in the journal Geophysical Research Letters.