In a statement released at the summit, the G8 leaders said, "We seek … the goal of achieving at least 50 percent reduction of global emissions by 2050, recognizing that this global challenge can only be met by a global response, in particular, by the contributions from all major economies …"

While some observers applauded the long-term goal, critics said the agreement lacked tough, short-term objectives. It calls only for "the development and deployment of low-carbon technologies in ways that will enable us to meet our sustainable economic development and energy security objectives."

As leaders such as German Chancellor Angela Merkel said they were "satisfied" with the pronouncement, Phil Clapp, an expert in climate change at the Pew Environmental Group, told The New York Times it actually weakened language the G8 adopted at last year's meeting in Germany.

"The emissions reduction goal is extremely weak," Clapp said. "The science shows that we have to reduce 80 to 90 percent from current levels to avoid the worst impacts of climate change."