U.S. President Barack Obama said on Thursday the world had made "important strides" towards arresting climate change by agreeing to limit warming, but U.N. chief Ban Ki-moon said it was simply not enough, Reuters reported.
"This is politically and morally (an) imperative and historic responsibility ... for the future of humanity, even for the future of the planet Earth," said Ban.
Major economies meeting in Italy agreed to restrict global warming to 2 degrees Celsius (3.6 Fahrenheit) -- a development that was unthinkable 12 months ago, before Obama was elected president of the world's second biggest greenhouse gas emitter.
But the Group of Eight rich nations failed to persuade top emitter China and India to join in a push to reduce global greenhouse gas emissions by 50 percent by 2050 -- a blow to efforts to secure a new U.N. pact by year end.
And Canada and Russia appeared to turn their back on the G8's stated aim of cutting its emissions by 80 percent by 2050 within 24 hours of it being announced.
In Washington, there was a setback for Obama's global warming bill when the committee pushing it forward suspended work on it until after the Congress recess ends in September -- raising doubts whether it can be delivered in time for Obama to present it at December's U.N. climate summit in Copenhagen.
Obama, at his first meeting of Group of Eight leaders, said the "days are over" when his country fell "short of meeting our responsibilities" on greenhouse gas emissions.
"Ice sheets are melting, sea levels are rising, our oceans are becoming more acidic and we have already seen its effects on weather patterns our food and water sources and our habitats."
"Every nation on this planet is at risk and just as no one nation is responsible for climate change, no one nation can address it alone."
Obama said he understood China and India's qualms about reducing energy consumption when rich industrial powers had "a much larger carbon footprint per capita".
"They want to make sure that they do not have to sacrifice their aspirations for development and higher living standards," Obama told reporters at the G8 summit in L'Aquila in Italy.
"Yet with most of the growth in projected emissions coming from these countries, their active participation is a prerequisite for a solution," said the American president