If the U.S. doesn't do something soon to dramatically reduce greenhouse gas emissions, it could cost the country $3.8 trillion annually from higher energy and water costs, real estate losses from hurricanes, rising sea levels and other problems, an environmental group predicted Thursday.

The study by the Natural Resources Defense Council and Tufts University comes as Congress is set to take up controversial global-warming legislation next month.

The Lieberman-Warner Climate Security Act of 2008 would create a carbon "cap and trade" system that would force power companies, manufacturers and the transportation industry to cut their greenhouse-gas emissions by 4 percent below 2005 levels by 2012 and 71 percent by 2050.

Opponents of the bill, led by the U.S. Chamber of Commerce, the National Association of Manufacturers and petroleum producers, say it would be disastrous for the economy.

"Any way you look at it, Lieberman-Warner will result in major disruptions of our economy, soaring energy prices and millions of lost jobs," Keith McCoy, vice president of the National Association of Manufacturers, said in a statement this month.

McCoy's group estimates the Lieberman-Warner bill would reduce the nation's economic output by as much as $669 billion annually and result in up to 4 million job losses. Other studies by government and business groups predict that such legislation would hurt cost U.S. businesses and consumers anywhere from $444 billion to $4.8 trillion by the year 2030.

Last month, the U.S. Energy Information Administration predicted that consumers' average annual home energy bills could rise by $30 to $723, in part because the bill would force power companies to use more expensive alternative energy sources instead of cheaper coal.

Authors of the new study, however, say that not enacting the Lieberman-Warner proposal would be much more costly.

"If you think it's expensive to do something about climate change, this tells you how expensive it will be to do nothing about climate change," said Tufts economist Frank Ackerman, who conducted the study.

The Southeast — and Florida in particular — could face some of the biggest costs, according to the study. Losses from Atlantic and Gulf Coast hurricanes, which could become much more intense because of global warming, would result in $422 billion in economic losses annually.

Increased energy and water costs related to droughts and higher air conditioning costs in Georgia, Florida, Texas and other Southern states could suck another $1 trillion annually out of the economy, the study predicts.

The estimates, however, don't include many factors.

Carbon-emission reductions resulting from new technologies now in development, for instance, aren't included.

Neither are the effects of state and regional emissions regulations in the works for Florida, California, the Northeast and other parts of the nation.

Dan Lashof, director of Natural Resources Defense Council's Climate Center, said such efforts are a good start but that federal legislation is what's really needed to significantly reduce greenhouse gas emissions.

State and regional efforts "are not comprehensive enough," he said. "What we need is a comprehensive national (strategy) for driving down emissions over time."