A lawyer for the Attorney General of Canada fielded questions Thursday about the line between provincial regulation of greenhouse gas emissions and the federal government's responsibility.

Sharlene Telles-Langdon said greenhouse gases have "cumulative dimensions" because emissions don't respect provincial boundaries once pollutants are emitted into the air.

She said each province's emissions contribute to Canada's overall greenhouse gas levels and every jurisdiction must work toward a solution.

"It's not necessary for each of the systems in each province to be the same to achieve the objectives of the legislation or to address the matter of national concern," Telles-Langdon said at a hearing in the Saskatchewan Court of Appeal. "What is necessary is that a pricing system applies throughout Canada."

The Saskatchewan government has asked the Appeal Court to rule whether a federal carbon tax is constitutional. The province argues it is not because the tax isn't being applied equally across the country.

Saskatchewan, New Brunswick, Ontario and Manitoba do not have their own carbon-pricing plan and will be subject to Ottawa's tax starting in April. The federal government's carbon price starts at a minimum at $20 a tonne and rises $10 each year until 2022.

"It's not singling out any one province," said Telles-Langdon. "There's been a national benchmark set. Provinces can enact their own legislation. It is assessed against that benchmark."

The federal government says it can levy a carbon tax because climate change and greenhouse gas emissions affect everyone in Canada and are a national concern.

"One province's refusal or failure to sufficiently regulate greenhouse gas emissions impacts Canada as a whole," Telles-Langdon said.

Ottawa has pointed to a section of the Constitution that states the federal government can pass laws for the "peace, order and good government of Canada."

Appeal Court Chief Justice Robert Richards interjected Telles-Langdon's arguments about jurisdiction.

"You want to try to make room for both levels of government for legislative respect of greenhouse gas issues," he suggested.

He also asked for a clear explanation from Telles-Langdon about "how it is you're slicing and dicing."

She said Ottawa looks at greenhouse gases from a national perspective and that constitutionally provinces are unable to address Canada's overall emissions level.

Lawyers for Saskatchewan and other carbon tax opponents argued in their submissions Wednesday that Ottawa is overreaching into provincial jurisdiction.

The lawyers said the case is not about climate change at all, but the divisions of power.