In 2015, Justin Trudeau gambled on sustainable development. He bet that promising to balance the economy and the environment would win over voters – and it did. They flocked to the Liberals, at least partly because of this commitment. Will it work again in 2019?Conventional wisdom is against it. Trudeau may have been lucky once, we hear, but it's hard to campaign from the middle ground. His position on the environment grows more complicated by the day; and people are getting confused and concerned.In this view, smart campaigns rely on simple, clear messages, which usually means standing firmly for or against something. That works best in the binary language of 'right vs. wrong' or 'us vs. them,' rather than fuzzy talk about 'working together' or 'balancing interests.'Take Jason Kenney's reaction to the carbon tax. You won't find any talk there of balancing the economy and environment. Kenney's approach is to delcare all out war on the “green left.”Perhaps this will win him the next election, but it's very bad policy. It not only divides the community, it misrepresents the nature of the conflict. At bottom, the pipeline debate is not a disagreement over goals or even values. Ordinary people don't oppose a prosperous economy, and few if any are out to harm the environment.Where these people disagree is on the risks pipelines pose for the ecosystem – and much of this is tangled up in misinformation and misunderstanding. People are not very good at assessing risk. They don't know how likely it is that a tanker will run aground or that an earthquake will damage a pipeline. Figuring this out takes lots of data and teams with special skills.Moreover, this kind of evidence is less than perfect. It is about probabilities, not certainty and that can confuse people. Militants on both sides exploit this by filling in the uncertainty with speculation and rumours, then tell ordinary people to trust what they feel.As a result, they gravitate to conclusions that reflect their interests. Someone who earns a living in the oil patch is likely to underestimate the risks, while someone living by the harbour in Vancouver may overestimate them.But if risk assessment is an imperfect science, it is rigorous enough to support informed decision-making on pipelines. The challenge is to put it to work the right way – to use it to define clear tests and standards for whether a pipeline should be approved and what must be done to make it safe.Of course, this would mean making real changes in how governments make policy. And that takes a leader who is willing to be rigorous about evidence AND fair about interests. Most importantly, he/she would need the public's trust.Enter Justin Trudeau circa 2015. That's how he pitched sustainable development in the campaign. He called on Canadians to take a more evidence-informed and collaborative approach to these issues; and he asked them to trust him to lead the way. So, how is he doing?The Liberals have been busy on the environment. So far, their most important work revolves around a clever plan to trade a pipeline for a carbon tax – and I don't mean to sound cute. From a policy perspective, it's an ambitious scheme that checks some important boxes: it puts a price on carbon, leaves room for building some pipelines, and accommodates the provinces by inviting them to design their own pricing schemes.And for the first time, it gets the whole country working together to advance sustainable development — or at least that's how it seemed for a while. Now the wheels may be coming off the bus. Alberta and BC are at loggerheads over Kinder Morgan. Doug Ford promises to scrap the carbon tax if he wins in Ontario. Jason Kenney is vowing to make war on environmentalists. Saskatchewan Premier Scott Moe is off to court to challenge Trudeau on carbon pricing.Trudeau insists he will do what he must to keep the plan on course. And he should – up to a point. If he goes too far in one direction – say, putting too much government money behind a private sector pipeline – all the talk of finding a reasonable balance between competing interests will come crashing down.That said, those who care about sustainable development should take the long view. The policy is less than perfect but change on this scale is hard. At least now they have an oar in the water. If they pull it back out, what then?The Jason Kenneys promise to take them back to the future — to choose the economy without the environment. Industry, especially, may find this appealing, but everyone should take a hard look at what's really on offer. Something out there has changed. The old days are gone and vowing to crush the green movement won't bring them back.On the contrary, the likely result is a rancorous and divisive debate that will paralyze both governments and industry. We choose that path at our peril. The rationale choice is to stay the course — to work toward a “reasonable balance” between economy and environment, based on the best available information and a rigorous assessment of the risks. Mr. Trudeau?Dr. Don Lenihan is an internationally recognized expert on public engagement and Open Government. He is currently advising The Ottawa Hospital on an engagement plan to develop its new Civic Campus – a $2 billion, 10-year project. He also co-chairs the Open Government Partnership's Practice Group on Open Dialogue and Deliberation. Don can be reached at: [email protected] or follow him on Twitter at: @DonLenihan