WASHINGTON (CNN) -- A Bush official told skeptical senators Wednesday that the administration has aggressively fought climate change for the last six years, saying the White House believes "the earth is warming and humans are the leading cause."

Dr. Bill Brennan, an assistant secretary at the National Oceanic and Atmospheric Administration (NOAA), testified before Wednesday. He told senators that the Bush White House has spent $29 billion on climate change, insisting that's more than all other nations combined. His words follow a similarly-worded White House press release sent out last week and indicate a new phase in the administration's PR on the issue.

Democratic senators fired away at Brennan's assertions, pointing to program budget cuts and questioning whether the administration has launched any serious plan to combat climate change.

"You guys are not responding," said Sen. John Kerry, D-Massachusetts. "This is the most serious dereliction of public responsibility I've ever seen."

The hearing was the latest to look at whether the Bush administration pressured federal scientists into minimizing evidence of climate change. Experts gave disputing testimony, with NOAA scientist Thomas Knutson insisting he has never perceived any interference with his work. Environmental consultant James Mahoney, however, told senators the Bush administration has squashed key reports and conclusions from its scientists.

Senators from both parties found common passion on the problem itself. Commerce Chairman Daniel Inouye, D-Hawaii, told the panel he's worried the American public doesn't understand the danger and will change their habits too late.

"Most people will conclude that at this moment they have not reached that level of fright," he said, "when will something happen so that people will come to this level of fright?"

Ranking Republican Ted Stevens, R-Alaska, responded, "Is anyone scared? I'm scared!"

Stevens represents Alaska where he says glaciers and permafrost are melting. The Alaska senator insists the evidence on global warming has changed his opinion and policy so that he now advocates much tougher fuel efficiency standards.