A 1-meter increase in sea level doesn't sound like much.

But the 3.3-foot rise would be enough to flood 90 percent of New Orleans, 33 percent of Virginia Beach, Va., and 18 percent of Miami, according to scientists.

With the release of a University of Arizona-led study earlier this week, evidence continues to mount that the polar ice sheets are melting at a rate that could profoundly affect coastal regions unless greenhouse gases are reduced worldwide, scientists say.

"Sometime before the end of this century, we will cross that critical threshold where the Earth will be committed to 4, possibly more, meters (13.2 feet) of sea-level rise that could occur at a rate as high as a meter per century," said Jonathan Overpeck, a UA professor and atmospheric scientist.

He and other scientists aren't certain when that point will be reached, but he believes it could be in the middle of this century.

Overpeck is co-author of the UA study that examined the effect ocean warming will have on the Greenland and Antarctic ice sheets and predicted how much water temperatures could increase by the end of the century.

The research, published in the Nature Geoscience journal, predicts warmer oceans will cause the polar ice sheets to melt faster and cause sea levels to rise higher than previously thought.

The study comes as climate change and its potential impact on the Earth's environment remain a hotly debated topic. Some skepticism about whether climate change is occurring lingers, but much of the debate now centers on whether the causes are man-made. There is little political agreement internationally on how aggressive nations should be in trying to reverse the trend. Some leaders don't think anything can be done at all.

A report by the National Research Council, released earlier this year, said climate change is likely caused by man-made greenhouse-gas emissions and poses significant risks to humans and the environment. President Barack Obama has called for reduced pollution, and the federal stimulus directed more than $80 million toward clean-energy technology. Obama also ordered federal agencies to reduce greenhouse-gas emissions by 28 percent by 2020.

In December, a U.N. conference of 193 countries agreed to set up a fund to help developing nations use greener technology and methods. But the group delayed for a year decisions on reducing carbon emissions.

Scientific studies show that temperatures at the North and South polar areas are warming and their ice sheets are shrinking; the trend is only expected to continue.

In March, a nearly two-decade study of satellite images by NASA found that the Greenland and Antarctic ice sheets are losing mass at an accelerated rate. The authors predicted that sea levels could rise as much as a foot by 2050, but they cautioned that there are many uncertainties in predicting ice loss.

Researchers are trying to better quantify the effects of global warming on polar ice sheets.

Much of the research has focused on the effects of warmer air, or atmospheric warming, on ice sheets. The UA study is unique in that it examined ocean warming. Ice sheets can also lose mass when the surrounding water warms.

UA scientists say ocean warming is perhaps even more damaging to ice sheets than atmospheric warming.

The reason is that water has a much larger heat capacity than air. An ice cube in a warm room will take several hours to melt, said UA professor Jianjun Yin, the lead author of the recent study. An ice cube in a cup of warm water will disappear in just a few minutes.

Yin's research predicts that subsurface ocean temperatures could rise as much as 3.6 degrees Fahrenheit along the Greenland coast and by nearly 1 degree along Antarctica by the end of the century. A few degrees may not sound like much. But because ice sheets are bathed in cold water, an increase of even a degree or two can have a profound effect, scientists say.

If the ocean warms as predicted, "we should see acceleration in the ice melt," said Joellen Russell, a UA professor who coauthored the study.

The UA study didn't quantify the exact impact the ocean warming would have on sea levels, but researchers at UA and other institutions say sea levels could rise by as many as 3.3 feet by the end of the century.

A growing number of studies published in the past couple of years try to predict sea levels more precisely.

In 2007, the Intergovernmental Panel on Climate Change, an international body of scientists who assess climate change, estimated that sea levels could rise by up to nearly 2 feet by the end of the century. But that report didn't take into consideration the cumulative effects of melting sheet ice. Many scientists believe those projections are now too conservative.

UA's findings are similar to research published in May by the Arctic Monitoring and Assessment Program, an international group headquartered in Oslo, Norway, that conducts research and advises governments. That study, which looked at atmospheric temperatures, predicted Arctic temperatures in the fall and winter will increase over the next century. It also projected sea levels will rise 3 to 5 feet by the end of the century.

But a lot of questions remain.

Although scientists have estimated how much sea levels could rise over a given century, they are unsure of the pace of the rise within that century. They also want to better pinpoint how much sea levels could rise at specific locations along coasts.

If nothing is done to reverse global warming, fortifying the coasts to prevent flooding could be an expensive proposition, said Overpeck, the UA scientist.

"That money will come from taxpayers across the country, including Arizona," he said.

Climate change also could affect the state in other ways.

A notable change would be higher temperatures, including 130-degree heat in July by the end of the century, Overpeck said.

Scientists say that although it would be hard to stop global warming, the effects could be moderated.

"America's Climate Choices," a recent report released by the National Research Council, makes several recommendations, including substantially reducing greenhouse-gas emissions. The report advises investing in energy-efficient and low-carbon technologies as well as participating in international climate-change response efforts. U.S. efforts alone won't be enough, the report concluded.

The report said the U.S. will have to both contribute to and learn from other countries' efforts.

Reach the reporter at anne .ryman@arizonarepublic.com.