OTTAWA -- Environment Minister Catherine McKenna says Canada's entreaties to the U.S. on the Paris agreement didn't take hold, despite arguing it would be better for Americans to be at the negotiating table to help set the rules for the global climate deal.

U.S. President Donald Trump followed through last week on a promise to withdraw from the Paris climate agreement, reached at the end of 2015 and signed onto by former president Barack Obama the next year.

McKenna says she, Prime Minister Justin Trudeau and Foreign Affairs Minister Chrystia Freeland had "been very active" making the case that the deal was good for the U.S. and for the world.

"But clearly that message didn't resonate," she said in an interview with Evan Solomon, host of CTV's Question Period.

Two months ago, McKenna had told Question Period Trump would reconsider his pledge to quit the agreement, which would have seen the U.S. try to cut emissions by 26 to 28 per cent from 2005 levels by 2025.

"There's certainly been positive signals from the president [that he won't pull out]," McKenna said in an interview that aired April 1.

Now, McKenna says she's very disappointed.

"The Paris agreement was always designed to have flexibility. So the U.S. had the flexibility, and the Trump administration the flexibility to decide what actions they were going to take in the United States," she said.

"They didn't take that advice and I'm actually just not clear about what the U.S. position is."

It could take four years for the U.S. to withdraw from the agreement, McKenna said.

Trump also said he wanted to renegotiate the terms of the deal, which McKenna says is impossible.

"You can't renegotiate the Paris agreement. It's in force, although 90 per cent of the rules remain to be negotiated. I've made this case to my American counterpart that [it's] better to be at the table and be negotiating the rules," she said.

Conservative international trade critic Gerry Ritz says it's now time "for some solid reflection" on Canada's next steps on the climate file.

"Canada can show some leadership here, but for us to completely clean up our house and no one else come on board even, like China, until 2030, what are we doing?" Ritz told Solomon.

"We're 1.6 per cent of the whole global problem, so we can go to zero if you can get to that point technically, and it still wouldn't make a difference globally. So there's a lot of work to be done."

Ritz says the Conservatives support Canada's current emissions reduction targets, which were set under the previous Conservative government. Trudeau and McKenna committed to a 30 per cent cut from 2005 levels by 2030.

New Democrat MP Nathan Cullen said that while he's not surprised by Trump's move to pull out of the Paris deal, he's disappointed -- the same way he feels about Canada's targets.

"I don't think our targets are very good, frankly. I don't think Trudeau picking up [former prime minister Stephen] Harper's carbon targets are what Trudeau campaigned on," he said.