TOYAKO, Japan,  - Leaders of the world's top industrial powers ended a summit Wednesday with pledges to act on soaring oil and food prices, but failed to bridge deep differences with poor nations on fighting climate change. US President George W Bush hailed his last Group of Eight summit, at which rich nations agreed to at least halve global greenhouse gas emissions by 2050, as "very productive". "I'm pleased to report that we've had significant success," Bush said before he left the resort venue where the annual summit was held in the mountains of northern Japan. Emerging nations invited to attend a special summit on tackling global warming however declined to back the G8's much-touted carbon emissions goals, saying they amounted to empty rhetoric. The global economy, under threat from skyrocketing oil and food prices and also being battered by the subprime mortgage crisis that has infected global financial markets, preoccupied the leaders. The G8 powers - Britain, Canada, France, Germany, Italy, Japan, Russia and the United States - account for two-thirds of the world's gross domestic product. Their leaders said in a joint statement that while global growth had "moderated," they remained positive on the future. They called for efforts to bring down oil prices, which have jumped five-fold since 2003, as well as the soaring cost of food which has set off riots in parts of the developing world. "There's a need to improve transparency on the oil market," Japanese Prime Minister Yasuo Fukuda told a news conference. G8 leaders also called on all countries to end export restrictions on food to allow supplies to be sent to countries that most need them, Fukuda said. The summit was dominated by discussions on global warming amid growing concern that rising temperatures caused by carbon emissions are threatening entire species of plants and animals. The rich nations' club on Tuesday agreed on the need for a global emissions cut of at least 50pc by 2050, a step praised by G8 leaders as progress after years of hesitation by Bush. "This, against a 1990 baseline, is a clear step forward. But we must go further," UN Secretary General Ban Ki-moon said. But Fukuda said he believed the baseline was current levels and developing countries slammed the statement as too weak. Leaders including Chinese President Hu Jintao and Indian Prime Minister Manmohan Singh tussled with rich nations at a special expanded summit on Wednesday. The deadlock between rich and developing nations has held up talks on reaching a new climate treaty by the end of 2009 in Copenhagen - a goal set in December at a UN-backed conference in Bali. "Climate change is one of the great global challenges of our time," the 16 leaders said in a statement. "Our nations will continue to work constructively together to promote the success of the Copenhagen climate change conference." But their statement said only that rich countries would implement their own goals for cutting greenhouse emissions while developing major economies would also take action, without proposing any numbers.