UNITED NATIONS, N.Y. -- Prime Minister Justin Trudeau joined world leaders who rushed to put their signatures Friday to a global treaty on climate change in hope of bringing it into force.

Now comes the hard part.

Canada is nowhere near its target of reducing greenhouse-gas emissions by 30 per cent by 2030. Emissions are still inching up. A national plan is still being worked out.

Indeed, if you've got an idea how all this could work, please tell the federal government. Really -- it wants your advice.

Trudeau used his appearance at the United Nations signing ceremony to promote the new website, www.canada.ca/climateaction, and the Twitter hashtag where the government is seeking suggestions from Canadians.

"We're looking for ideas on how to reduce emissions," he told a news conference.

"On the best way to move forward with carbon. And (on) how we can best prepare for and, if possible, avoid the impacts of climate change.... It's important that all Canadians be part of this conversation."

He promised not to give up. In his first speech to the UN General Assembly hall, Trudeau said: "Today, with my signature, I give you our word that Canada's efforts will not cease."

The agreement enters into force once it is ratified by 55 countries accounting for 55 per cent of global emissions, which is now expected to happen, given the resounding reaction Friday.

The event broke the record for most first-day signatures for an agreement of its kind. Secretary-General Ban Ki-moon said at least 175 countries signed on: "It is a very moving day for me, personally."

The pact negotiated last year differs from the old Kyoto accord in several important ways:

Every major emitter has set individual targets under this one -- unlike Kyoto which excluded fast-developing countries.

It does not include broad global emissions targets, nor is it binding.

It does include a mechanism that will report on each country's progress -- it's a peer-pressure strategy.

The broad goal of the agreement is to keep global temperatures from rising less than 2 C from pre-industrial levels, to stave off the most catastrophic effects of rising sea levels.

Trudeau received a warm reaction. He was mobbed for photos, walking between meetings. The president of Colombia joked that he's now the most popular leader in the Americas.

And he drew perhaps the most ovations of any leader who spoke to the assembly. One came when he described the particular challenge facing poorer countries: How to cut emissions, when their economies are growing fastest?

"They shouldn't be punished for a problem they didn't create, nor should they be deprived the opportunities for clean growth that developed nations are now pursuing," Trudeau said.

Developing-country delegations applauded again when he mentioned the $2.65 billion his government budgeted for international-assistance programs geared towards clean-energy programs.

Trudeau's domestic opponents weren't singing such praises.

The Conservatives said he hasn't been straight with people. They pointed to the parliamentary budget officer's finding that hitting that target could shave one to three per cent off the national economy by 2030.

"The Liberals are misleading Canadians by saying everything is a win-win, while not accounting for the true economic costs," said a statement from Tory critic Ed Fast.

"Fighting climate change is serious business and Canadians need to be prepared to have a frank discussion about who pays for it."

The Conservatives said they're not actually opposing the emissions target -- which they set when they were in power. They just said the prime minister needs to be more honest about its costs.

During his New York trip, the prime minister touted an all-of-the-above approach where additional oil production can coexist with cleaner technology, and more wealth gets spent on energy innovation.

One prominent environmental economist says the country has actually made progress.

Dave Sawyer of EnviroEconomics projects the country could get halfway to its targets -- with emissions declining 15 per cent by 2030, after levelling off in a few years, if provincial governments respect their already-announced plans.

"Current policies are actually delivering a lot more than people think," he said. "There are still gaps."