They should be rejoicing. For years — decades really — environmentalists have been pushing the federal government to take on the job of regulating the pollution that belches out of the nation's smokestacks, exhaust pipes, and oil and gas wells.

What they wanted was to have one central authority on which public pressure could be brought to set the appropriate standards and enforce their compliance.

Pierre Trudeau wouldn't do it. Neither would Brian Mulroney or Jean Chrétien or Paul Martin. All passed important environmental laws of one sort or another. (Mulroney's Environmental Protection Act was supplanted by Chrétien's, which has now in turn been supplanted by Stephen Harper's.)

But none would commit to true national regulation. Air emission standards in this country, whether from cars or coal-fired power plants, have always been governed by a series of unenforceable national or federal-provincial objectives, many laudable, some not so much.

Until now. The Harper government's just-introduced Clean Air Act, maligned though it's been by environmental groups, represents the first time Ottawa has stepped up to the plate and promised to set standards for the full range of emitters: From cars and off-road vehicles to electrical generating facilities, oil and gas developers, refineries and petrochemical producers, smelters, cement makers, the forestry industry and consumer products, including new dishwashers and household appliances.

From the green perspective, Harper's an unlikely hero — a small-government proponent who seemed to pooh-pooh the Kyoto agreement during the last election campaign and is now pledging to impose tough new compulsory limits on all manner of industry and smog producers.

That's the good news, from an environmental perspective at least.

The bad news: It will take at least 14 years under the proposed agenda for the first set of hard caps to kick in — during the 2020-2025 target period — at least as they apply to climate-warming greenhouse gases.

In the meantime, Ottawa intends to set what it calls intensity standards per barrel of oil (or some other measurement), which means that actual emissions will continue to rise if production does, though perhaps not quite as fast as they are today.

The car industry may come under the new regime as early as the 2011 vehicle year, but that will depend on the emission standards set by the U.S. Environmental Protection Agency — an important distinction.

Since the early 1980s, Canada has followed the EPA rules, albeit as part of a series of voluntary agreements with the car industry, which have never been fully verified. But the EPA doesn't regulate greenhouse gas emissions for cars, and has shown little interest in doing so even though some U.S. jurisdictions, notably California, are taking that step.

Ottawa's authority

Greenhouse gas targets, then and now

The Kyoto goal: Reduce GHG emissions levels to six per cent below 1990 levels by 2012

• Actual target: 563 million tonnes
• Current (2004) emissions: 758 million tonnes
• Current Kyoto gap: 195 million tonnes
• Projected gap in 2012: 270 million tonnes

The Conservative goal: Reduce GHG emissions levels to between 45 and 65 per cent of 2003 levels by 2050

• 2003 levels of greenhouse gases: 754 million tonnes
• 45 per cent of that: 340 million tonnes
• 65 per cent of that: 490 million tonnes

Harper's plan is laudably straightforward. It appears to hit every industry and household group with equal fervour. It promises serious reductions (though over a very long period), standards that would be no less than the U.S. in every category (we currently lag: see the accompanying interactive feature, The air we breathe and thorough monitoring.

What's more, it calls a spade a spade. The volatile chemical compounds that are the main ingredients of smog (ground level ozone, sulphur dioxide and the nitrogen oxides) have been reclassified as "air pollutants." (They were called "toxic substances" in the old Environmental Protection Act.) The greenhouse gases (primarily carbon dioxide and methane) are labelled, naturally enough, greenhouse gases.

That straightforwardness, mind you, could be a huge problem.

Simply put, Ottawa has never had clear absolute authority to regulate on environmental matters in this country. In fact, the courts have tended to favour the provinces, which is why Messrs. Trudeau, Mulroney and Chrétien shied away from compulsory national standards.

The environment was not on anyone's mind when the Fathers of Confederation assigned powers to the respective levels of government in 1867.

The provinces, broadly, were given the authority to regulate commerce; the feds the power to set criminal laws and deal with things that cross borders, which is how Ottawa gets to put its nose in the environmental jar.

In 1997, Ottawa won a seminal and close (5-4) Supreme Court decision upholding federal water pollution laws in the face of a determined challenge from Quebec and its big utility Hydro-Québec.

What was important about that decision was that the court found the pollutant in question was a "toxic substance," which meant Ottawa had the authority to regulate based on its power to set criminal laws and protect from harm.

Changing that toxic-substance definition, as the Harper government has, raises an interesting constitutional question: Has Ottawa now tied its own hands?

Will the provinces object?

If the provinces see this new regulatory scheme as an intrusion on their jurisdiction, they could take Ottawa to court over it. (Industry could as well if it doesn't like the regulations that are to be negotiated over the next 12 months. Though its initial reaction has been positive.)

This new Clean Air Act does say it hopes to harmonize federal regulations with provincial efforts, but that may not be enough of a carrot for some to go along.

In the past, Quebec has been very jealous of its own environmental powers. Alberta and B.C. have also taken Ottawa to court over water regulations and other environmental disputes.

Three years ago, when Kyoto talk was heating up, the Alberta government passed its own Climate Change and Emissions Management Act to forestall being corralled under a Liberal Ottawa regime. (Like Harper's, it proposes an "emissions intensity" test rather than a hard cap: GHG emissions are to be cut over time but only in relation to Alberta's gross domestic product.)

Ontario, too, threatened recently to go its own way if Ottawa targets its auto industry unfairly.

Harper's response, it seems, judging by this legislation, is to stretch out the deadlines, which is what has upset the environmentalists — the long grace periods make a mockery of Canada's Kyoto commitments, most say — and then just gore every ox at the same time.

It is a different approach than past federal governments have tried. When Ottawa won that Supreme Court decision over Hydro-Québec in 1997, it elected not to take the jurisdictional ball and run with it, apparently feeling this was a bigger fight than it needed to take on.

Instead, it turned around and negotiated "harmonization agreements" with the provinces, to come up with common standards and reduction targets, at least for those "toxic substances" that are now labelled air pollutants.

Environmentalists didn't much like the harmonization agreements, viewing them as bowing to the lowest common denominator.

And, judging by their early reaction, they don't appear to like Harper's approach now, feeling that he's weakened his hand with unnecessary wording changes and a timetable that leaves too much wiggle room to be effective.