Sea levels along coastlines in the United States will rise about one foot by 2050, with larger increases on the East and Gulf coasts, according to a comprehensive new report by federal climate scientists.

Oceans have already risen about one foot in the last century, as climate change melts glaciers and ice caps around the world. But the pace is accelerating, scientists warn, and the next 30 years will see the same amount of sea level rise as the previous 100.

"It's like history is repeating itself, but in fast-forward," says William Sweet, a sea level rise expert with the National Oceanic and Atmospheric Administration (NOAA) and one of the authors of the new report.

People living in coastal cities are already facing encroaching seas. Every extra inch of ocean water scours beaches and sea walls, exacerbates flooding during hurricanes and makes it more likely that salty water will undermine buildings, and infiltrate sewers, storm drains and drinking water reservoirs.

The report gives the most concrete and certain sea level projections ever published for the U.S. The authors of the report are 24 top climate scientists from across the federal government and academia. And advances in computer models and real-world information about rising seas make it possible to see the future with more clarity than ever.

"This is unique in that we're having a much clearer, confident expected outcome," Sweet says. "So folks can really plan and prepare."

Sea level rise varies dramatically for different parts of the U.S. coast. The ocean is not like a bucket of water that rises uniformly as more liquid is added. Ocean currents push more water into some areas than others. Ice in different regions melts at different rates. In many parts of the world, sea level rise is worse because coastal land is sinking.

The new report adds up all those factors to give regional estimates for different parts of the U.S. The authors predict about a foot and half of sea level rise for the Gulf Coast by 2050, with particular hot spots from Texas to Mississippi, where extraction of underground oil, gas and drinking water is causing the land to rapidly collapse into the rising ocean water.

There are similar hot spots in the Mid-Atlantic region, including Annapolis, Md. and Norfolk, Va. Overall, the East Coast is projected to experience a little more than a foot of sea level rise in the next 30 years.

Sea level rise is happening more slowly on the West Coast, including much of southern and western Alaska, the report finds. The authors predict about six inches of sea level rise by 2050. Hawaii and island territories in the Caribbean will see a little more than half a foot of sea level rise.

"This is unfolding in front of our eyes. Whether you're in Miami or Charleston or Norfolk or Annapolis," Sweet says. He says cities that are not yet inundated should take notice now. "It's best to plan before the problems surface. But it's not to say we can't engineer our way out of this. We will find ways to live with the water."

Accelerating sea level rise may require that humans change where and how we build homes, offices, roads and anything else that is better dry than wet. Right now, development in flood-prone areas is increasing, despite climate change. "We are moving towards the flood risk," says A.R. Siders, a climate change researcher at the University of Delaware who was not involved in the new report. "We're building faster in areas that are prone to sea level rise and flooding."

Sea level rise also has implications beyond the coasts. "Sea level rise matters to the entire U.S. whether you live on the coast or not, because so much of our economy is based in these areas," says Siders.

Beyond 2050, the report makes clear that humans have a choice: reduce greenhouse gas emissions and control sea level rise, or keep burning fossil fuels and face oceans that are two, three or even 10 feet higher than today.