The statement was seen as something of a breakthrough from a White House, which has sought to question the science supporting claims of global warming.
Their White House-commissioned report is now being reviewed by the president as he prepares to face European leaders angered by his attack on the Kyoto Protocol on climate change.
A panel from the National Academy of Sciences said a leading cause is emissions of carbon dioxide from burning fossil fuels.
Correspondents say this could put pressure on the administration to shift its position on global warming.
"Temperatures are, in fact, rising," the panel warned. "Greenhouse gases are accumulating in the earth's atmosphere as a result of human activities, causing surface air temperatures and subsurface ocean temperatures to rise," the report said.
It warned that "national policy decisions made now and in the longer-term future will influence the extent of any damage suffered by vulnerable human populations and ecosystems later in this century".
White House response
Next week, Mr Bush will meet European Union leaders in Gothenburg, Sweden, where he hopes to present an alternative to the Kyoto agreement that he denounced in March.
Responding to the report, National Security Advisor Condoleezza Rice said Mr Bush "takes extremely seriously what we do know about climate change, which is essentially that there is warming taking place".
The statement was seen as something of a breakthrough from a White House, which has sought to question the science supporting claims of global warming.
Ms Rice is seen as part of a group of White House insiders sympathetic to environmental concerns.
These include Secretary of State Colin Powell, Treasury Secretary Paul O'Neill, and Environmental Protection Agency Administrator Christine Whitman.
Kyoto objections
In her statements to reporters, Ms Rice reiterated the reasons that the Bush administration - like the US Senate - rejected Kyoto.
"One would want to be certain that developing countries were accounted for in some way, that technology and science really ought to be important parts of this answer, that we cannot do something that damages the American economy or other economies because growth is also important."
She said that a cabinet-level committee was working to formulate a US alternative to the Kyoto agreement.
Reports suggest that such a proposal might include voluntary measures for reducing emissions, preserving forests and farms that can absorb greenhouse gases, and emissions credits that could be traded from clean industries to polluting ones.
Mr Bush's spokesman said any proposals presented in Sweden would be general rather than specific.
Swedish Environment Minister Kjell Larsson, whose country holds the rotating presidency of the EU, told the BBC he not believe a plan that did not include mandatory targets would automatically be acceptable to the EU.
"I don't believe there is any kind of voluntary system that could be satisfactory. This is too big, too general an issue to be dealt with by voluntary agreement," he said.
No recommendations
The National Academy of Sciences was not asked to recommend policies, and did not do so.
The panel of 11 scientists produced its 24-page report in less than a month.
One scientist who reviewed a draft of the report for the academy told The New York Times newspaper that the White House should not be surprised at the speed or the conclusions of the report.
"They asked a string of questions that might have been appropriate in 1990," the unnamed scientist said.
"Where have you been the last decade?" he asked the administration.