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.