G8 leaders have endorsed a goal of cutting greenhouse gas emissions in half by the year 2050, but critics say the declaration is meaningless because it appears to lack a firm base year.

The Group of Eight declaration was issued Tuesday, as Prime Minister Stephen Harper and the other leaders planted trees and posed for photographers in the Japanese resort village of Toyako.

Harper praised the declaration as a breakthrough from the 2007 G8 summit in Germany, when the United States and Russia would only agree to "seriously consider" such a plan.

"Russia and the United States have both agreed (to the declaration)," Harper said. "This is the first time either of those countries have conceded the necessity of having a long-term, mandatory goal for reduction."

But Marthinus van Schalkwyk, South Africa's minister of environmental affairs and tourism, said the declaration was useless without stronger targets.

"To be meaningful and credible, a long term goal must have a base year, it must be underpinned by ambitious midterm targets and actions," he said. "As it is expressed in the G8 statement, the long-term goal is an empty slogan."

It's unclear what base year G8 countries will use to measure their reductions. A Canadian official told The Canadian Press countries would be free to choose their own base level, while Reuters quoted Japanese Prime Minister Yasuo Fukuda as saying it would be "current levels."

Whichever the case, Antonio Hill of Oxfam International denounced the announcement as a stalling tactic. "At this rate, by 2050 the world will be cooked and the G8 leaders will be long forgotten," he said.

The declaration calls on developing economies like China and India to cut emissions, which is seen as a diplomatic win for Canada and the U.S.

South Africa, Mexico, Brazil, India and China are to meet Wednesday with the G8 leaders to discuss climate change and other issues.

The five nations issued a statement Tuesday urging developed countries to set an interim target of at least a 25 per cent cut below 1990 levels by 2020.

A step forward?

Harper said Tuesday's declaration shows G8 countries are willing to work hard at long-term goals at reducing GHG emissions.

There is "a firm recognition of all countries that to make these objectives effective, even in the long term, we have got to have mandatory participation by all major economies, by all major emitters," he said.

The complex declaration holds that all major economies must sign on to a future plan to curb GHG emissions, but with different roles and responsibilities.

China and India, two of the biggest emerging economies, were excluded from having to make GHG cuts under the 1997 Kyoto Protocol.

But as their economies have grown, the emissions of the two Asian giants have risen significantly. China is now considered to be the world's biggest total GHG emitter, although its per-capita emissions are still about one-quarter of those in the U.S. and Canada.

The world is currently negotiating a successor treaty to Kyoto, which expires in 2012. Harper has previously said any new deal must include China, India and the U.S.

"What we want to see is an effective agreement that will help avoid dangerous climate change," Environment Minister John Baird told Canada AM from Japan. "If we want to fight climate change, we need all oars in the water."

The world will hold a major climate meeting in Copenhagen next year.

Canada's Conservative government has said it won't try to meet this country's Kyoto commitment of a six per cent cut below 1990 levels by 2012.

The Tories have blamed Liberal inaction, but they killed a 2005 Liberal plan that would have made Canada Kyoto-compliant -- albeit through buying emissions credits. The Tories fiercely opposed that approach.

The Conservative plan focuses on industrial emitters and sets a target of a 20 per cent cut below 2006 levels by 2020. Critics have said even if the Tory plan works, Canada wouldn't reach its Kyoto target until 2025.

Oil prices

The leaders have also called on oil-producing nations to increase production in an attempt to reverse the trend that has seen crude's price shoot up by nearly 50 per cent since January.

Analysts expect the trend to continue in the second half of this year.

Harper said Canada, which he has described as an emerging energy superpower, has expanded its supply of oil.

A call for cheaper oil, however, would appear to conflict with the goal of dramatically reducing GHG emissions over time.

"I think what we want to see is do what we can to increase the supply so that causes the price to go down," Baird said. "There's no doubt that with the emerging economies of China and India, we're going to see an increase in demand."

Baird noted that in terms of gasoline, Canada is short of refining capacity. New refineries planned for Ontario, Quebec and the Maritimes will take years to come on stream.

Harper said G8 leaders also discussed ways to reduce demand and increase energy efficiency. They like the idea of Britain's Prime Minister Gordon Brown to establish an energy forum in which producing and consuming nations could discuss ways to prevent price surges in the future.

With a report by CTV's Graham Richardson and files from The Canadian Press