The Kyoto Protocol, an international pact aimed at reducing the world's greenhouse gas emissions, came into effect Wednesday, although Canada still has not spelled out its own plan for compliance.

But CBC News has learned that the emission targets for large Canadian polluters have been cut back from the original federal plan that was unveiled in 2002.

Canada has committed to chopping its greenhouse gas emissions by six per cent from 1990 levels by 2008-2012.

Environment Minister StÃ©phane Dion said Tuesday that Canada's plan to implement the agreement won't be in the Feb. 23 budget, but will be announced "in the weeks after the budget."

Ottawa's initial plan, unveiled in 2002, required large industrial emitters to cut back by 55 megatonnes as part of an overall 240-megatonne target.

But sources tell CBC News that the new deal lowers that to between 40 and 45 megatonnes.

The higher targets were unpopular on two fronts.

Alberta has long protested that it will bear a disproportionately high share of Kyoto's costs because of its energy-based economy.

On Tuesday, however, the Alberta government confirmed that it is negotiating a special agreement with Ottawa to allow the province to maintain control over environmental rules affecting the oil and gas industry as the Kyoto plan takes effect.

Meanwhile, large businesses say Canadian manufacturers will find it harder to compete with American rivals that have no Kyoto commitment to pay for.

The United States has not ratified the treaty, claiming it would damage the U.S. economy, and major developing nations like China and India are exempt.

The international agreement, negotiated eight years ago in Kyoto, Japan and ratified by 141 countries including Canada, is aimed at addressing the problem of global warming.

The accord imposes limits on emissions of carbon dioxide and other gases scientists blame for rising world temperatures, melting glaciers and rising oceans.

Implementation of the agreement has been delayed by the requirement that countries accounting for 55 per cent of the world's emissions ratify it. The goal was reached last year when Russia signed on.