WASHINGTON —A panel of scientists testified during a Senate committee briefing Wednesday that New Orleans may go underwater by the end of the century.

The “latest climate science” briefing called by Senate Environment and Public Works Committee Chairwoman Barbara Boxer, D-Calif.

No Republican on the committee, including Sen. David Vitter, R-La., who is the ranking GOP leader on the panel, attended the briefing that featured scientists discussing global warming.

Sen. Bernie Sanders, No Party-Vt., asked what the nation will look like at the end of the 21st century if fossil fuel emissions continue to skyrocket worldwide and the planet continues to warm at a rapid rate.

James McCarthy, a Harvard University biological oceanography professor, said human activities and climate change will cause the sea levels to rise 3 to 6 feet by then if the temperature rises by 8 degrees or so as substantial scientific research indicates.

“It’d make a huge difference in the Gulf of Mexico,” McCarthy said. “It’d make a huge difference for all our coastal cities.

“New Orleans is gone,” he said.

The Senate briefing came in advance of Thursday’s anticipated announcement by Sanders and Boxer that they would propose a new fee on carbon pollution emissions that would fund energy efficiency and sustainable energy technologies such as wind, solar, geothermal and biomass.

They said the proposal also would provide rebates to consumers to offset any efforts by oil, coal or gas companies to raise prices.

“I’d call it a shocking wake-up call,” Boxer said of the science briefing. “We heard certain parts of our country will be gone.”

Vitter opposes a so-called “carbon tax” that he has argues would cause lost jobs and severely hurt the oil-and-gas industry.

McCarthy said there is no general penalty for carbon emissions. “So we’re treating the atmosphere like an open sewer,” he said.

The oceans are rapidly warming and helping to power up storms and hurricanes, McCarthy said. Climate change is contributing to dramatic weather events such as longer droughts and even more extreme snow events, he said.

Practically, American Meteorological Society President J. Marshall Shepherd said, look at what he called the Cheerios test of climate change and droughts causing increased grain and milk prices. Likewise, climate change affects other groceries costs, insurance costs and property values, scientists said, not to mention the nation’s infrastructure.

John Balbus, a National Institute of Environmental Health Sciences senior adviser for public health, said the U.S. is behind most other developed nations.

“So long as the rest of the world sees the U.S. is not acting, it opens the door for them not to act,” Balbus said.

U.S. Rep. Henry Waxman, D-Calif., who is the ranking Democrat in the House Energy and Commerce Committee, complained that Republicans argue the science is “unclear” on climate change. “But, of course, they don’t want to hear from scientists,” he said, arguing that his Republican-led committee has refused multiple requests to invite scientists on the topic.

Waxman said Republicans contend everything is fine because carbon emissions dropped by 2 percent in the U.S. last year, even though 2012 was the hottest year ever on record.

“The science is clear,” said Shepherd, of the American Meteorological Society. He said that there are a few dissenters amongst a strong consensus. “The literature is overwhelming.”

Although the U.S. made some progress last year, Shepherd said, increased emissions in developing nations such as India and China more than offset what happened in America.

“We’re not a self-contained climate,” Shepherd said of the U.S.

What stands out is the “rate” of planetary warming that is occurring at record levels, he said. What has occurred the past few decades would take thousands of years without human influence, he said.

“It’s like putting the Earth’s climate on steroids,” Shepherd said, likening climate change to the surge of home runs in Major League Baseball during the so-called steroids era.

Putting the planet on steroids through climate change, he said, dramatically increases the likelihood of severe weather events just like actual steroids significantly contributed to the increased home run rates in baseball.