Washington ? Rising sea levels, sweltering temperatures, deeper droughts, and heavier downpours — global warming’s serious effects are already here and getting worse, the Obama administration warned on Tuesday in the grimmest, most urgent language on climate change ever to come out of any White House.

But amid the warnings, scientists and government officials seemed to go out of their way to soften the message. It is still not too late to prevent some of the worst consequences, they said, by acting aggressively to reduce world emissions of heat-trapping gases, primarily carbon dioxide from the burning of fossil fuels.

The new report differs from a similar draft issued with little fanfare or context by George W. Bush’s administration last year. It is paradoxically more dire about what’s happening and more optimistic about what can be done.