The Liberal Party is continuing to unveil policy plans for Canadians to ponder over the summer, launching a green agenda that includes a national carbon-pricing proposal and free access to the country's national parks during the celebrations of the 150th anniversary of Confederation.

Liberal Leader Justin Trudeau said as Canada's prime minister he would lead a delegation of the country's first ministers to the UN's climate-change conference in Paris in December. Within the following three months, Mr. Trudeau would hold a first ministers' meeting to put together a "framework to combat climate change," including national emissions-reduction targets.

"Make no mistake, the Liberal Party will be putting a price on carbon," Mr. Trudeau said in Vancouver as he unveiled his "plan for Canada's environment and economy."

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The environmental program is part of a series of announcements – including a middle-class tax cut and a 32-point plan for a "fair and open government" – that the Liberals will put to the electorate in the Oct. 19 next election. Mr. Trudeau is hoping not only to persuade Canadians to dismiss the Conservatives, but also to select the Liberal Party over the NDP for a "real change" in government.

"For 10 years, we have had a government that has done nothing to understand that the world has changed, that you cannot build a strong economy without protecting and preserving our environment," Mr. Trudeau said. "That is exactly what we want Canadians thinking about as they enjoy this extraordinary country through the summer months."

The NDP, which is also looking to attract voters who are tired of the current Harper government, said it offers a much clearer plan to force polluters to pay for the environmental damage that they cause.

"It looks half-baked to me," NDP MP Malcolm Allen said of the Liberal announcement. "Mr. Trudeau is only saying, 'The provinces will tell me what to do,' so it seems that it's a hope and a wish and a prayer."

The Conservative Party argued that by promising to put a price a carbon, the Liberals will force Canadian families to pick up the tab.

"Justin Trudeau is proposing a carbon-pricing scheme that will increase the costs of everything including gas, groceries, electricity," said Natural Resources Minister Greg Rickford.

Mr. Trudeau made his announcement near Vancouver's Jericho Sailing Centre, where he took lessons some 30 years ago as a young teen. Flanked by dozens of supporters against a backdrop of blue sky, mountains and the Burrard Inlet, he said his long-time relationship with nature has shaped his environmental views.

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As part of their new plan, the Liberals are promising to restore $25-million in funding to Parks Canada, while offering free entry into all of Canada's national parks in 2017. In following years, the parks would be free for children and new immigrants within one year of obtaining their citizenship.

The Liberals would also follow a growing worldwide trend by creating "green bonds," which could be used by the private sector to develop alternatives to fossil-fuel energy sources.

"The bond will leverage the federal government's ability to provide more affordable loan guarantees for clean-energy projects, and provide Canadians with the opportunity to invest in clean technologies," the Liberal plan said.

The Liberals are also promising to overhaul Canada's environmental-assessment process, stating the current system fails to protect the environment but also paralyzes the exportation of resources to foreign markets. The Liberal plan would provide "robust oversight and thorough environmental assessments of areas under federal jurisdiction," while ensuring that Canadian citizens and experts are heard throughout the process.

The assessment would also include "an analysis of upstream impacts and the greenhouse-gas emissions resulting from the projects," a proposal that was applauded by various environmental groups on Monday.

Mr. Trudeau said he would strike a deal with the Ontario government to finalize the creation of Canada's Rouge National Urban Park, located in the Greater Toronto Area. The idea has been heavily promoted by the Conservative government, but the provincial Liberals pulled back their portion of the land in a protracted dispute with Ottawa over environmental protection earlier this year.