The California Democrat, who chairs the Senate Environment and Public Works Committtee, presented a "Climate Hero" award Monday to the George W. Bush Presidential Center on the campus of Southern Methodist University in Dallas.
The building achieved the coveted LEED, or Leadership in Environmental Energy and Design, Platinum certification for its sustainable design, construction and operation.
"It was a pleasure to see first-hand the library's innovative and energy efficient designs and to honor these important achievements," Boxer said Monday.
Former first lady Laura Bush accepted the award.
"It is really terrific to receive the inaugural Climate Hero Award from Senator Boxer," Bush said.
What a difference five years can make.
In a Senate hearing in September 2008, as Bush's time in office wound down, Boxer described the Republican president's "disturbing record" on the environment.
"Unfortunately, instead of reviewing accomplishments - we look back on years filled with environmental rollbacks that serve special interests, and do not serve the American people," Boxer said at the time.
She accused the Bush Environmental Protection Agency of weakening environmental regulations and ignoring the advice of its own scientists on the threat of global warming.
The Bush EPA record on global warming "could hardly be worse," Boxer said then.
But Monday's award didn't honor Bush's legacy - it honored the building that houses it.
Boxer plans to present another Climate Hero award to Bill Clinton's presidential library in Little Rock, Ark., later this year.