The G-8 did set a long-term commitment to reduce their carbon emissions by 80 percent by 2050. But they made no shorter-term target, despite warnings from a U.N. panel that they must cut emissions between 25 percent and 40 percent by 2020 to keep average global temperatures from rising more than 2 degrees Celsius above levels 150 years ago.

Most scientists agree that even a slight increase in average temperatures would wreak havoc on farmers around the globe, as seasons shift, crops fail and storms and droughts ravage fields.

Countries like China and India — the next generation of big polluters — want the industrial countries to commit to reducing carbon emissions by 40 percent over the next decade before they commit to any reductions of their own. Without that commitment from the G-8, they refused to make any targets of their own.

"The ground for a breakthrough can only be prepared if the G-8 leaders reach consensus on the midterm binding goals of cutting greenhouse emission and stop asking the developing nations to act first as an excuse for their not committing to the binding goals," China's official Xinhua News Agency said in a commentary earlier this week.

The failures earned the G-8 a sharp rebuke from U.N. Secretary-General Ban Ki-moon.

"The policies that they have stated so far are not enough, not sufficient enough," Ban said Thursday. "This is the science. We must work according to the science. This is politically and morally imperative and a historic responsibility for the leaders for the future of humanity, even for the future of planet Earth."

Obama did announce Thursday that the Group of 20 major economies would take up the climate financing issue at their meeting in September in Pittsburgh — a move environmentalists said could help break the logjam while sending developing countries a signal that the G-8 is serious about financing.

"To get the finance ministers focused on this topic is a useful way of pushing forward one of the key agenda items," de Boer said.

He stressed that it was perfectly understandable for developing countries to refuse to commit to reduction targets when they have no idea how they're going to pay for them or what industrialized countries are going to commit to in the short term.

That failure of the G-8 "made it very much a black box for the developing countries ... because if you don't know what the industrial countries are going to commit to by 2020 and you don't know what financing is going to be on the table for developing countries, it becomes very much a leap of faith."

Annie Petsonk, lawyer for the Environmental Defense Fund, said that the outcome of the talks were natural given that there are five months to go before the Copenhagen treaty summit.

"It's no surprise if developing nations aren't rushing in to sign up for new goals and targets right away," she said. "This is a negotiation after all. But the starting gun has sounded and everyone knows they need to go home and start thinking seriously about what they can bring to the table."