MONTREAL - The Conservative government has been warned that drilling for shale gas could boost carbon-dioxide emissions, encroach on wildlife habitat and sap freshwater resources.

The risks are outlined in briefing notes prepared last spring for Natural Resources Minister Christian Paradis.

The documents, obtained by The Canadian Press under the Access to Information Act, focus on the potential of shale-gas development in Quebec.

They also highlight the promise and perils of tapping the many large reserves found across Canada.

"Canada has significant shale gas resources and industry is aggressively exploring and developing them," the briefing notes say.

They warn the process of releasing natural gas from shale -- called hydraulic fracturing or "fracking" -- could draw heavily on freshwater resources and significantly increase Canada's overall carbon-dioxide emissions.

The documents also say projects in areas without infrastructure may require the construction of roads, drill pads and pipelines, which could create "extensive habitat fragmentation" for wildlife.

Because of environmental and public-health concerns, the debate over shale gas has heated up in Quebec in recent weeks.

The province has vast reserves of natural gas trapped in the rock beneath the St. Lawrence River lowlands.

The natural-gas industry and the provincial government see lucrative opportunities in the shale. They argue that tapping into it would create jobs and pump cash into the Quebec government's bank account.

But opponents, including residents who live near exploration sites, say the gas projects must be stopped because of the risks.

The concerns have spurred the Quebec government to slow down the process. The province announced recently it will hold public hearings and conduct an environmental review on the issue this fall.

But the head of the Quebec Oil and Gas Association insists shale-gas projects would use only two per cent of the water needed for the pulp and paper industry.

And Andre Caille said groundwater would barely be touched by contamination.

"Very little, for instance, compared to other industrial sectors," he said in an interview Tuesday.

The amount of carbon dioxide emitted from drilling would be offset by savings in transporting natural gas from other jurisdictions, he said.

Caille said the industry would also work to limit the impact on wildlife.

"We want our footprint to be as light as possible," said Caille, a former head of Hydro-Quebec.

Paradis was not available for comment Tuesday, his office said.

Shale-gas exploration and development is in its early stages in British Columbia, Alberta, Ontario and New Brunswick.

Paradis' briefing notes say major players in the gas industry started acquiring land rights on Quebec's shale reserve in 2005. The area is now fully leased.

Quebec is not the only North American jurisdiction where there are concerns over exploiting shale gas.

New York state called a temporary moratorium in August on fracking -- a drilling technique in which water, chemicals and sand are blasted down a well, causing enough pressure to free the gas.

The issue has also been raised in several other states, prompting the U.S. Environmental Protection Agency to launch a study to examine the environmental and human-health risks of fracking.

An oil and gas expert from Cornell University, who is completing a study on the environmental impacts of shale-gas operations, says enormous amounts of energy are needed to access it.

"It's being promoted as environmentally clean energy and sort of a transitional fuel into the future to help with global climate change, and I don't think it's either one," environmental science professor Robert Howarth said in an interview.

He also says carbon dioxide released from shale-gas wells is relatively minimal -- it's the methane leakage that creates the biggest climate-change effect.

"Methane is an incredibly potent greenhouse gas," Howarth said.