____________________________________ When federal scientists rallied on Parliament Hill to protest the Harper government's cuts to science they had a telling, if awkward, chant.

“What do we want?  Evidence-based decision-making.”

“When do we want it?  After Peer Review.” Last October, Canadians elected a government committed to transparency and evidence-based policy.  This commitment is a positive step towards a healthier and more prosperous future.But let's not expect this to be easy.  Acting on evidence will often create more conflict than it resolves.  This is especially the case for government actions to improve our health and environment.Take the example of salt in processed foods.  Evidence shows that our diet has an excess of salt that contributes to heart disease.  But the food processing industry expresses concerns about the technical feasibility of further reductions and claims that consumers prefer saltier foods.If scientists conclude that an industrial pollutant needs to be reduced to protect our health or the environment, the emitters will not quietly acquiesce.  The response will be some version of the standard objections.  They will claim that the science is not proven; it will cost too much or the technology is not available.  And Canada would lose jobs because our competitors do not have to spend money on equivalent actions.If Canadian scientists conclude that we should limit the amount of a problem chemical in consumer products, they could recommend that we act before our trading partners do.  Then business will view the proposed action as creating inefficiencies for global production lines or an unreasonable barrier to trade.If scientists recommend that a marine area should be set aside to protect endangered species and fish breeding habitat, the resource sectors are certain to complain.  There are fish there to catch today.  There may be oil or minerals to extract in the future.Meanwhile environmental and health advocates will press for stronger or quicker action and get media attention.The public generally applauds when governments protect the environment.  When threatened by dirty water or smog we all see the problem and understand the harm.  Actions to require vehicles and fuels to be cleaner, for example, are broadly supported.  But this is not always the case.Greenhouse gasses are invisible, and the greatest threats lie far in the future.  As a result, climate change actions that increase household costs get lukewarm support, if that.  Concerns are often raised about cleaner technologies (think windmills.)So despite strong science predicting future harm from a changing climate, the public remains ambivalent.  And most industry stakeholders continue to push back against action that other countries have not already taken.  They warn of competitive disadvantages and job losses.  Many talk of leadership but no one wants to go first.The climate change issue is about to heat up.  New science and increased damage from wildfires, droughts and floods have created a greater sense of urgency.  This has set the stage for world leaders to agree to the more ambitious goal of limiting global warming to 1.5 degrees Celsius.  Despite this, few are prepared for the scale of effort that is consistent with the evidence.You may remember the debate about road salt.  There was ─ and there still remains ─ clear scientific evidence justifying efforts to use less salt in order to reduce its impact on waterways during the spring melt.  There was a plan to press municipalities to adopt techniques such as the use of brine that used less salt but still did the job.  Political support vanished, however, when opponents focused on road safety.Following the evidence will be straightforward when science guides governments to decisions that industry accepts and the public supports.  But when scientists make the case for actions that are against vested interests, or are potentially costly and inconsistent with the public's perceptions, the debate will be heated.Often these stakeholders have legitimate points. That's why many use the term evidence-informed decisions, rather than evidence-based decisions, to acknowledge the need for governments to take into account social and economic factors.But too often there is an instinctive resistance to reasonable changes.  The challenge for politicians is to make the right judgement call after examining all the factors.  The one certainty is that many decisions will be controversial.So while there is no question that governments should use evidence when deciding how to protect our health and the environment, we should all prepare for heated debates.Marjory Loveys spent ten years as a senior policy advisor in the Office of Prime Minister Jean Chretien.   To view other articles in this series, click here.