The leader of the third-place BC Greens is setting a government-or-nothing threshold for next month's provincial election, asking voters to hand the party a breakthrough – even with a platform that includes an increased carbon tax, maintaining bridge tolls and the possibility of mobility pricing for drivers.

Andrew Weaver told The Globe and Mail's British Columbia bureau on Monday that the people of British Columbia – particularly those who have traditionally abstained from casting a ballot – will be drawn to his "principled" approach as his party aims to build on its first-ever seat, won in 2013.

"When you look around our society, people are ready to pay a little bit more," Mr. Weaver said, suggesting that as long as voters know where their money is going, they will willingly finance solutions to social problems.

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On the carbon tax, the Greens are proposing to increase the environmental levy over four years from the current $30 a tonne to $70 a tonne, generating revenue for transit and other projects sought by communities. Ottawa already plans to raise the national tax to $50 a tonne by 2022.

As the BC Liberals and the BC NDP debate cutting or eliminating tolls on the Port Mann and Golden Ears bridges in the Lower Mainland, Mr. Weaver defended the idea of keeping the tolls in place.

"It's tough to be principled – I get that," said the noted climate scientist at the University of Victoria. "It would be really easy for us to stand up and say, 'We're going to eliminate the tolls on the Vancouver bridges, too.' But that's wrong, because you need to pay for that infrastructure, and we want to discourage people from using their cars."

No polling has put the Greens anywhere close to forming government, but support for the party has been showing signs of growth during the campaign, particularly on Vancouver Island.

Mr. Weaver said his party's internal polling supports that assessment and that merely holding onto his seat or even quadrupling the party's standings in the legislature would, in his eyes, not be the mark of success. The Greens have candidates in 83 of B.C.'s 87 ridings.

The party received 8.15 per cent of the vote in the 2013 election, its lowest support in four elections. Its vote share peaked in 2001 with just more than 12 per cent.

Mr. Weaver cast the campaign as a high-stakes affair – not just for his party but for his political career as well. He said that if he remains the only Green member in the legislature after May 9, he would serve the term but then not continue as an MLA. "I did not get into politics to make it a career path," he said, because in his view the legislature is "broken" and people are not being put first in decision-making.

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Mr. Weaver was also dismissive of the suggestion that the Greens could split the vote, drawing support from either the Liberals or the New Democrats and swinging results in some ridings.

"Nobody owns any vote. It is offensive to the average voter to think that somehow a party owns your vote," he said.

He said the non-voter essentially dominated the last provincial election – a reference to the 45 per cent of British Columbians who did not cast a ballot.

The Green Party Leader said it was too early to talk about whether he would support a minority BC Liberal or BC NDP government if the Greens win enough seats to bargain.

"I will say the BC Liberals and the BC NDP simply cannot be trusted with a majority government."

Mr. Weaver said he is looking to this week's televised leaders' debate – the last of the campaign – to make his pitch to voters. He said Wednesday's debate will allow for more clashes among the candidates. "I am excited about that," he said.

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His comments Monday came as his party released its full election platform, a 98-page document that forecasts operating deficits in the second and third years of a Green government's mandate but a $216-million surplus in the final fiscal year. He is also promising a new ministry for mental health; vowing to match Ottawa's $460-million investment in public-transit infrastructure; and offering free daycare for working parents with children under the age of three.

The party plans to pay for its commitments by getting rid of tax credits, enacting a one-percentage-point increase in the corporate tax rate and raising taxes on those who earn more than $108,000 a year.