By LESLIE KAUFMAN – New York Times.

The nation’s scientific establishment issued a stark warning to the American public on Thursday: Not only is global warming real, but the effects are already becoming serious and the need has become “pressing” for a strong national policy to limit emissions of heat-trapping gases.

The report, by the National Research Council, an arm of the National Academy of Sciences, did not endorse any specific legislative approach, but it did say that attaching some kind of price to emissions of carbon dioxide, the main greenhouse gas, would ideally be an essential component of any plan.

“The risks associated with doing business as usual are a much greater concern than the risks associated with engaging in ambitious but measured response efforts,” the report concludes. “This is because many aspects of an ‘overly ambitious’ policy response could be reversed or otherwise addressed, if needed, through subsequent policy change, whereas adverse changes in the climate system are much more difficult (indeed, on the time scale of our lifetimes, may be impossible) to ‘undo.’ ”

The report, “America’s Climate Choices,” was ordered by Congress several years ago to offer “action-oriented advice” on how the nation should be reacting to the potential consequences of climate change.

But the answer comes at a time when efforts to adopt a climate-change policy have stalled in Washington, with many of the Republicans who control the House expressing open skepticism about the science of climate change. Other legislators, including some Democrats, worry that any new law would translate into higher energy prices and hurt the economy.

Not only is the science behind the climate-change forecast solid, the report found, but the risks to future generations from further inaction are profound. Already, the report noted, sea level is rising in many American towns and the average United States air temperature has increased by two degrees in the last 50 years.

The report’s authors — an unusual combination of climate scientists, businessmen and politicians — said they were very aware that the political mood on climate change had changed significantly from when the committee was formed in 2009. Because the report was also about policy advice, the council named nonscientists, including Jim Geringer, a conservative Republican and a former governor of Wyoming.

Albert Carnesale, the chairman of the panel and a chancellor emeritus of the University of California, Los Angeles, said that he hoped the panel’s diversity and that many came to the job without “prior bias” would help sell it even to skeptical policy makers.

“It is an urgent problem to turn to, and what we’ve done differently is to look at this as a risk management problem,” Dr. Carnesale said.

While no one knows the exact shape of the risks, Dr. Carnesale said, we know that they are real enough to act on. And that they will be harder to act on as time passes. “We don’t know exactly when the tsunami will hit or how high it will be, but we know it is coming, and we should prepare,” Dr. Carnesale said.

But Representative Joe L. Barton, Republican of Texas, who has been leading the charge against further regulating carbon emissions, swiftly dismissed the council’s findings in an interview Thursday. “I see nothing substantive in this report that adds to the knowledge base necessary to make an informed decision about what steps — if any — should be taken to address climate change,” Mr. Barton said.

Although the report characterizes climate change as a problem that urgently needs attention, it stops short of making highly specific policy prescriptions, leaving that to lawmakers.

To many worried about climate change, that is a common flaw of such reports.

“This is the classic problem — the divide between scientific reality and political courage,” said Paul W. Bledsoe, a senior adviser with the Bipartisan Policy Center who has worked in Congress and with the White House on these issues. “The scientific organizations are reluctant to advocate detailed policy prescriptions, while political actors are tentative about the scientific realities.”

The report outlined four areas that demanded immediate action by the federal government.

For starters, it emphasized that reducing carbon emissions was critical to keeping the United States from having to make dire choices in the future. While stopping just short of recommending a carbon tax, the committee did praise its efficacy.

“Analyses suggest that the best way to amplify and accelerate such efforts, and to minimize overall costs (for any given national emissions reduction target), is with a comprehensive, nationally uniform, increasing price on” carbon emissions enough to “drive major investments in energy efficiency and low-carbon technologies,” the report said.

It also called on the federal government to play a much more active role in researching new technologies and in helping the nation adapt to the changes in the natural world that are already inevitable. Even with a reduction in carbon output, the report said, some climate change will continue to occur.

It noted that while many of the nations’ cities and states are taking steps toward mitigating carbon output and preparing for hotter, wetter conditions, it suggested that the federal government could help coordinate these activities while also encouraging more research and development.

“The federal government,” the report said, “should immediately undertake the development of a national adaptation strategy and build durable institutions to implement that strategy and improve it over time.” Finally, while this report was designed, in contrast to the United Nations Intergovernmental Panel on Climate Change, to be by Americans for Americans, the authors noted that climate change was a global problem and the nation had an obligation to remain engaged with the international community on possible solutions.