A Dalhousie University professor is "cautiously optimistic" the new Trudeau Liberal government will "unmuzzle" federal scientists, but warns the damage may take years to reverse.

"[The Liberals] made a pledge that right away [that] they're going to stop the muzzling of scientists," said Tom Duck, an associate professor of physics and atmospheric science. 

"Thank goodness for that, because we cannot have a national conversation on important issues like climate change without the experts weighing in."

Duck spoke with CBC Radio's Mainstreet on Friday.

The Conservative federal government has long been accused of restricting science through funding cuts and strict policies on how to speak with the media about scientific research.

Scientist rally

More than 200 government workers rallied in downtown Vancouver in May 2015 to protest the federal government's alleged muzzling and intimidation of scientists. (CBC)

A widespread survey in 2013 found hundreds of scientists had been asked to modify or exclude scientific information, and about half said they knew of cases where Canadian health and safety had been compromised as a result. 

The Conservatives denied the muzzling, saying instead it invested well in science and technology.

Brain drain hard to reverse, says scientist

This chilling effect forced many scientists to quit, retire or leave the country, including renowned oil spill expert Ken Lee who left Nova Scotia for Australia after a government cut in 2012, Duck said.

Halifax-based biologist Steve Campana told CBC — after retiring from the federal Department of Fisheries and Oceans in May — that he was silenced from even 'just talking about facts."

Steve Campana

Steve Campana says the stifling of science is hurting Canada. (CBC)

"I am concerned about the bigger policy issues that are essentially leading to a death spiral for government science," Campana said at the time.

"I see that is going to be a huge problem in the coming years. We are at the point where the vast majority of our senior scientists are in the process of leaving now disgusted as I am with the way things have gone, and I don't think there is any way for it to be recovered."

Liberal plan encouraging: Duck

Duck is encouraged by the Liberal plan to attend the climate change conference in Paris, but discouraged by the reluctance to commit to setting emissions reduction targets, he said.

Muzzled scientist

Manitoba protesters in 2013 bring out a muzzled scientist to illustrate their frustrations with the federal government. (Sean Kavanagh/CBC)

"That being said, I think we can proceed with this cautious optimism and see what happens. Of course, they have to get into place, assess these organizations and understand the damage before they can act," Duck said.

Duck said he wants federal scientists able to lead public debate using facts on issues such as climate change and energy.

"I really think this is going to be a generational rebuilding project," Duck said.

"It's going to be very, very tough to repair."