In what's being billed as one of the most ambitious steps to address climate change in U.S. history, the Environmental Protection Agency today announced it is choking off carbon emissions from coal-fired power plants.

We know it's a bold move, because environmentalists love it and business groups hate it.

Love it or hate it, the move also sends a message to other countries that claim an interest in fighting climate change.

U.S. President Barack Obama will long be out of office before anyone knows if today's announcement on carbon dioxide limits lives up to the hype or is full of hot air, but the move has been made.

It provides the U.S. administration something concrete to point at when chastising other countries (including Canada) for not doing enough to curb their emissions.

And this isn't just about bragging rights or clean air — it's business.

In the fight to build the Keystone pipeline in order to ease the flow of land-locked Alberta oil, the U.S. has pointed to Canada's lack of action on climate change as a barrier to approval.

Canada is already jumping to the defence of actions already taken.

In 2012, the government introduced new regulations to curb greenhouse-gas emissions from coal-fired power plants (although a month later it also watered down those regulations), a fact Conservative MP Rob Merrifield is happy to point out.

"When it comes to coal … that is something they are way behind on, that's unfortunate, but it's good to see [Obama] catching up."

Coal vs. oil and gas

When looking at issues as complex as this, however, trying to compare apples to apples becomes far more difficult.

It's true that Canada got a jump start when it comes to curbing coal emissions, but it's what those emissions represent that makes the difference.

In Canada, coal-fired power plants make up 11 per cent of the country's total greenhouse-gas emissions.

In the U.S., they pump out 38 per cent of that country's CO2 and are the largest single source of emissions.

Canada's single largest source is the oil and gas industry, which produces 25 per cent of the total.

Kathryn Harrison, who teaches political science at the University of British Columbia and is an expert on climate change policy, says, "I think the more important part of today's announcement is that the U.S. is going after the source of carbon pollution that is most significant for its economy."

"In contrast, Canada has delayed time and again proposed regulations for upstream oil and gas emissions," Harrison adds.

Asked today if Canada will follow suit on cutting emissions, Prime Minister Stephen Harper kept his answer focused on coal.

"Not only have we already been acting, but under the regulations this government has already brought forward we will have a 150 per cent larger reduction than those in the United States."

Another difference, though, is in the bigger picture.

With this announcement, the U.S. reckons it is on track to meet its Copenhagen pledge to cut emissions by 17 per cent by 2020.

In contrast, with the actions taken so far in Canada, the federal government said last year it's only halfway to meeting its Copenhagen pledge.