Prime Minister Yukio Hatoyama and U.S. President Barack Obama reaffirmed at their summit Friday the shared goal of achieving an 80 percent cut in greenhouse gas emissions by 2050 and supporting efforts by "the poor and most vulnerable" nations to combat climate change.

In a "joint message on climate change negotiations," the two leaders agreed that it is "vital that we achieve a successful outcome" at the Dec. 7-18 U.N. climate conference in Copenhagen that had been arranged in a bid to produce a deal on a new framework on fighting global warming.

Hatoyama and Obama endorsed a pledge by the Group of Eight major economies in July in L'Aquila, Italy, to halve global greenhouse gas emissions by 2050. However, they did not touch on an emissions reduction goal by developed countries by 2020, as it is the focal point of the current U.N. climate negotiations.

Hatoyama hopes to achieve a 25 percent cut in the nation's heat-trapping gas emissions from 1990 levels by 2020.

Shifting to low-carbon growth is indispensable to the health of the planet and will play a central role in reviving the global economy, Obama and Hatoyama agreed.

They urged all major economies to "take ambitious concrete actions" on setting emission reduction targets and be "subject to a robust regime of reporting and international review."

Sharp differences between developed and developing countries have cast a shadow on the Copenhagen talks.