The federal government's own environmental advisory body has lobbed sharp criticism at the Conservatives for their climate-change plan, accusing them of overestimating what the plan will accomplish.

In a report released Friday, the National Roundtable on the Environment and the Economy said the government's plan is vague, uses questionable accounting methods and exaggerated greenhouse-gas cuts it would result in.

The roundtable comprises leaders from business, labour, universities and environmental organizations.

The report examined 22 programs in the government's climate change plan and found that each either overestimated the amount of greenhouse gas emission reductions it would achieve or had insufficient information to reach any conclusion.

In some cases, the Tory plan double counts some of the cuts it is supposed to make, the advisory council says.

Friday's report comes as Prime Minister Stephen Harper prepares to head to New York next week to speak about climate change at a meeting of world leaders.

The prime minister has claimed at other world events that his government's plan will achieve real and specific greenhouse gas emission cuts.

With files from the Canadian Press