Inching beyond a pledge made a year ago, the world's top economic powers on Tuesday embraced a goal of slashing greenhouse gas emissions at least in half by mid-century, aiming to keep alive languishing talks on a new global warming pact. In a nod to the United States and others, however, the Group of Eight nations insisted it would be the whole world doing the cutting - rebuffing developing nations and environmentalists demanding rich countries first make their own commitments clear. “It has always been the case that a long-term goal is one that must be shared,” said Jim Connaughton, chairman of the White House Council on Environmental Quality. “So what the G-8 has offered today is a G-8 view of what that goal could be and should be, but that can only occur with the agreement of all the other parties,” he added, referring to nearly 200 countries involved in the UN talks. The G-8 powers also agreed to explore ways to reduce the impact of biofuels on food prices amid concern they may be hurting the poor and adding to global warming. Biofuels, derived from organic materials such as palm oil and sugar beet, were once seen as a promising way to reduce greenhouse gas emissions blamed for global warming by cutting the use of fossil fuels. But some experts have warned that current biofuels policy could push up grain prices and cause greenhouse gas emissions rather than savings. Biofuels were a hot topic among leaders of Britain, Canada, France, Germany, Italy, Japan, Russia and the United States huddled in this spa resort in northern Japan, a senior Japanese foreign ministry official said. “Some leaders said it's necessary to study the (effect of the) use of biofuels and ethanol in particular,” he told reporters. The G-8 leaders pledged in a statement to “ensure the compatibility of policies for the sustainable production and use of biofuels with food security.” They vowed to “accelerate development and commercialization of sustainable second-generation biofuels from non-food plant materials and inedible biomass.” The British government said Monday it would slow the expansion of biofuels following a report that found they might increase greenhouse gas emissions and contribute to food price rises. The G-8 statement, released by host Prime Minister Yasuo Fukuda in an announcement with the verdant hills of northern Japan behind him, solidified a pledge made at the last G-8 summit in Germany a year ago to seriously consider such a target. But the move fell far short of demands by some developing countries and environmentalists pushing for deeper cuts by 2050 and a firm signal from wealthy countries on what they are willing to do on the much tougher midterm goal of cutting emissions by 2020. The G-8 also did not specify a base year for the 50 percent cut, meaning that the actual emissions reductions and their effect on the environment could vary widely. Reductions from 1990 levels, as in the Kyoto Protocol, would be far larger than cuts from 2005 levels, for instance. “Achieving this objective will only be possible through common determination of all major economies, over an appropriate time frame, to slow, stop and reverse global growth of emissions,” the statement said. Some developing nations complained bitterly, accusing wealthy countries of attempting to avoid responsibility for causing global warming. The US has long been the largest emitter, though some estimates say China has eclipsed it as No. 1. “To be meaningful and credible, a long-term goal must have a base year, it must be underpinned by ambitious midterm targets and actions,” said Marthinus van Schalkwyk, South African Minister of Environmental Affairs and Tourism. “As it is expressed in the G-8 statement, the long-term goal is an empty slogan.” The G-8 agreement - and the ecstatic praise it elicited among European countries usually more ambitious on climate change - reflected leading nations' attempt to avoid the serious shortcomings of the 1997 Kyoto accord. Kyoto, while considered by many a worthy first step, is also seen as deeply flawed by its failure to commit developing countries like China to emissions controls, prompting the US refusal to ratify it. In addition, many countries with reduction commitments, such as Japan and Canada, are falling seriously behind. Another dynamic is that US President George W. Bush is leaving office next January and both major candidates to succeed him are willing to go further in reining in American emissions. “It's sort of OK, let's take what we can ... and live to fight another day, and raise the really nitty-gritty issues when you have a new president,” said Alden Meyer, climate change point man for the Union of Concerned Scientists. The G-8 has been under pressure to voice commitments by wealthy nations to push forward stalled UN-led talks on forging a new accord to battle global warming by the end of next year. The new pact would take effect when Kyoto's first phase expires in 2012. The climate talks, however, have been plagued by divisions. Quickly developing nations have urged wealthy countries to take the first, toughest steps. The United States, Japan and others, meanwhile, say they want to hear what China and others are willing to do. The Europeans have pushed harder for rich countries to reinvigorate talks by making unilateral commitments. Germany, for instance, has pledged to cut emissions by 20 percent by 2020, and by 30 percent if other countries join the effort.