WASHINGTON - A federal advisory panel released a massive draft report Friday detailing the extent to which climate change is already transforming the nation’s landscape and Americans’ way of life, warning that these impacts will intensify in the coming decades, given the current rate of global carbon emissions.

The draft of the third National Climate Assessment – more than 1,000 pages compiled by more than 300 experts over the course of the past three years – sums up what has become increasingly apparent: The country is hotter than it used to be, rainfall is becoming both more intense and erratic, and rising seas and storm surges threaten U.S. coasts.

The report “represents a very thoroughly evaluated” scientific consensus on how global warming is affecting the nation and aims to help policymakers adapt “to the changes that are already happening and those we anticipate in the near future,” said Katharine Jacobs, assistant director for climate adaptation and assessment for the White House Office of Science and Technology Policy, who oversaw the report.

The draft was posted online Friday afternoon and will be subject to public comment starting Monday. It is scheduled to be finalized in March 2014, after senior policymakers in the administration sign off on its conclusions it receives the official imprimatur of the White House.

Climate activists and Democratic lawmakers said the assessment revealed gaps in the country’s effort to cope with both global warming’s near-term effects and to future emissions that will exacerbate these problems.

“This draft report sends a warning to all of us: We must act now in a comprehensive fashion to reduce carbon pollution or expose our people to continuing devastation from extreme weather events and their aftermath,” said Sen. Barbara Boxer, D-Calif., who chairs the Senate Environment and Public Works Committee.

Rick Piltz, who worked as a senior associate in the U.S. Climate Change Science Program and now heads the group Climate Science Watch, said the report offers President Obama a rare opening.

“He’s said he wants to lead a national conversation on climate change,” Piltz said. “He should start the national conversation.”

The overview tackles subjects ranging from ocean acidification to water scarcity, attributing many of these changes to greenhouse gas emissions released through human activities that burn fossil fuels.

Its executive summary states that not only have extreme weather and climate events become more frequent in recent years, “there is new and stronger evidence that many of these increases are related to human activities.”

The report adds that these changes are already exacting an economic toll: “Infrastructure across the U.S. is being adversely affected by phenomena associated with climate change, including sea level rise, storm surge, heavy downpours, and extreme heat.”