The Obama administration, in a massive, new report on the dangers of climate change, warns that global warming is already harming Americans and that conditions will worsen significantly if carbon emissions aren't reduced.

The National Climate Assessment, released as part of a White House effort to rally support for its environmental agenda, attributes a spike in volatile weather patterns directly to global warming -- and says the U.S. cannot afford to look at rising temperatures as a distant problem.

“What is new over the last decade is that we know with increasing certainty that climate change is happening now,” the report says.

"While scientists continue to refine projections of the future, observations unequivocally show that climate is changing and that the warming of the past 50 years is primarily due to human-induced emissions of heat-trapping gases," the authors add. "These emissions come mainly from burning coal, oil and gas, with additional contributions from forest clearing and some agricultural practices.”

The report notes that most of the 1.3- to 1.9-degree increase in temperature since 1895 has occurred since 1970 and that the last decade was the nation’s hottest on record. The authors of the report conclude that temperatures will rise another 3 to 5 degrees over the next century, even in a “lower emissions scenario.”

The White House is using the report as justification for President Obama’s regulations to cut down on carbon emissions, particularly greenhouse gases produced by power plants.

Critics have accused Obama of waging a war on coal and other traditional energy sources, but the White House is framing his actions as a matter of national security.

“Summers are longer and hotter, and extended periods of unusual heat last longer than any living American has ever experienced,” the report finds. “Winters are generally shorter and warmer. Rain comes in heavier downpours. People are seeing changes in the length and severity of seasonal allergies, the plant varieties that thrive in their gardens, and the kinds of birds they see in any particular month in their neighborhood.”

And the scientists who authored the report took direct aim at those attributing the recent surge in temperatures to natural developments.

“Climate has changed naturally throughout Earth’s history,” they write. “However, natural factors cannot explain the recent observed warming.”

Still, red-state Democrats up for re-election in November are wary of Obama's climate push and have distanced themselves from regulations they view as unpopular among their constituents.

Obama will conduct interviews with national and local meteorologists at the White House on Tuesday to highlight the report, and the president will frame climate change as a centerpiece of his remaining two and a half years in office.

Environmental groups criticized Obama for not focusing extensively on climate change in his first term and letting cap-and-trade legislation die on Capitol Hill without much of a fight.

In his second term, however, Obama has called for limits on carbon emissions from new and existing power plants and new fuel-efficiency standards, and has traveled the country to warn of the dangers of climate change.

The report comes as the administration is weighing whether to approve the Keystone XL pipeline, pitting green groups against many labor unions.

Conservatives say the president is merely placating his political base ahead of November's midterms and that he should devote more of his time to the economy.

The White House will attempt to localize the results of the behemoth report Tuesday.

The report finds that the Northeast has already been affected by heat waves, extreme rain and coastal flooding because of higher sea levels; the Southeast exposed to water shortages and more extreme events, particularly hurricanes; the Midwest subject to longer growing seasons, the Southwest facing more wildfires; and the Northwest experiencing earlier snow melt.

“If you want to try to side with the polluters and argue to the American public that climate change is not happening, today, tomorrow and certainly in the future,” White House senior adviser John Podesta said Monday, “that's going to be a losing argument.”

This article was posted at 8:30 a.m. and has since been updated.