Stephen Harper has changed his mind, reversed his field and is now going to the UN climate change conference in Copenhagen.

He didn't want to do it. Climate change is becoming the most divisive issue in this country since the fight over energy pricing in the 1970s and '80s. But he had no choice.

The man the prime minister has been counting on to shape a climate change policy that Canada would have to accept is now going to Copenhagen himself on Dec. 9.

So when U.S. President Barack Obama said he would "drop in" on the climate change summit, Harper knew that he as well had to pack his bags for Denmark.

Two environmental activists hang a mock Time magazine cover depicting U.S. President Barack Obama, in Hong Kong on Nov. 16, 2009. It is not just Canada following his climate lead. (Vincent Yu/Associated Press)

Still, you can't blame the PM for being a reluctant participant.

Because, while Copenhagen will not create the new all-binding treaty to supersede the Kyoto accord, it will almost certainly strike the political agreement to limit future greenhouse gas emissions.

And that process will force participant nations to outline just how far they are prepared to go to limit fossil fuel production within their economies — and how exactly they intend to do that.

Different goals

Obviously, this is going to be contentious issue. Nations rich and poor, developed and developing will jockey for position.

Developing countries like China will propose modest, flexible goals to reduce the amount of greenhouse gases produced in industrial production, the so-called "carbon intensity" targets that will move in lockstep with their growing economies.

The developed countries of the European Union — densely populated and with a generally moderate climate — will call for hard caps and real cuts in the amount of greenhouse gases produced.

Furthermore, they will warn of tariffs and other penalties on the goods imported into Europe from countries with less stringent requirements.

The wild card in this global warming game of high-stakes poker has been the United States.

Until his final years in office, former president George W. Bush had been reluctant to even admit greenhouse gas emissions needed to be curbed to deal with a warming climate. Then, when he did admit to the problem, he didn't offer up with any solutions.

Whatever Barack wants

President Obama came to office acknowledging the problem and vowing to deal with it. He just didn't say how until now.

His plan is to reduce greenhouse gas levels in the U.S. by 2020 to 17 per cent below what they were in 2005. Other than suggesting a "cap and trade" system, in which polluters could buy and sell emission credits from each other, the details of the Obama plan have been scarce.

However, that proposal fits closely with the approach that the Harper government has been planning to take. And that is the way the Conservative government wants it.

After coming to office as global warming skeptics, the Conservatives now say that Canada's greenhouse gas emissions will be curbed by 20 per cent from 2006 levels by 2020. And a cap and trade system with the United States is part of their plan, too.

In fact when you come right down to it, whatever the United States wants to do is part of the Canadian plan.

When they were in opposition, the Conservatives resisted Canadian ratification of the Kyoto protocol. They said its adoption would put Canada at a competitive disadvantage with the U.S., because the Bush administration was not going along.

Now, with Obama ready to adopt greenhouse gas standards, the Harper government understands that Canada will have to do the same.

Particularly if U.S. legislators enact penalties on countries with less restrictive regimes — much like some in the EU are threatening to do.

Don't forget Congress

Of course any plan the Obama administration puts forward will have to be adjusted, amended and perhaps even gutted by both houses of the U.S. Congress before it becomes law. And that won't happen until sometime late next year.

That is why the prime minister has been trying to low-ball Copenhagen and any plans to cap emissions.

In the meantime, Ottawa was planning to intensify lobbying efforts in Washington, and in the U.S. in general, to make sure Americans did not label oil from the Alberta tar sands "dirty" oil, subject to extra penalties that would make its development prohibitive.

If it can win that case, Ottawa might then make a national argument that accepting the American greenhouse gas targets is both sensible and necessary. But even then, the case would not be an easy one.

Alberta and Saskatchewan, rich with energy that produces pollution, currently want the "intensity" approach to targets favoured by the Chinese and a few other countries.

Quebec, rich in clean energy from hydro-powered electricity, says it will adopt targets similar to those in Europe. The Bloc Québécois says the Harper Conservatives are selling out to their political base in oil sands Alberta by not having the same standard.

Good reason, you would think, for Harper to stay away from Copenhagen and keep the greenhouse gas discussion as vague as possible.

It all seemed like a great idea, until Barack Obama changed his travel plans. And Stephen Harper felt he had to tag along.