Canadian author and journalist Naomi Klein has weighed in on the United States presidential contest, criticising frontrunner Hillary Clinton and voicing her support for rival Bernie Sanders in the race for the Democratic nomination.

In an interview with Al Jazeera's UpFront programme, which will air on Friday night, Klein took issue with Clinton's efforts to combat climate change.

The author of the best-selling books No Logo and This Changes Everything told host Mehdi Hasan that she does not trust the former secretary of state.

"I don't trust her because as secretary of state, when she had a huge megaphone to make this an issue, to show that she understands the connections between human security and climate, she didn't use the megaphone," Klein said.

She also criticised Clinton's links to major donors, saying her ties to corporations made her hard to elect.

"I think that Bernie Sanders could win in a general election. I actually think he is a significantly better candidate than Hillary Clinton," she said.

"The power of the socialism smear [campaign against Sanders], I think has really lost a lot of its punch."

Klein also discussed the climate efforts in her own country, Canada, under new Prime Minister Justin Trudeau.

"I think [Canada has] done some important things, but what they're doing on climate is not nearly enough,” she said.

"I think Trudeau wants us to love him,” she added. “And because of that, that gives us more to work with."

Despite her passionate efforts to tackle climate change through her advocacy, books and films, Klein admitted that she leaves a substantial carbon footprint through her international travel.

"My huge sin is flying," she said. "You know, I wrote in a book that I finally lost my frequent flyer status and cut my flying by 10 percent, but even though I try to do as much as I can by Skype, I've been flying way too much."

Mehdi Hasan's interview with Naomi Klein will air on Al Jazeera's UpFront on Friday, March 18 at 1930GMT. It will be available at the same time online at www.aljazeera.com/upfront.