A panel of senior statesmen known as the Elders on Friday called for renewed efforts to conclude a world climate pact by the end of 2015 and appealed for a "carbon-neutral" planet by 2050.
"Given the compelling weight of evidence, it can be hard to understand why anyone is still dragging his or her feet on the coordinated action needed to reduce greenhouse gas emissions," the group said in a statement.
"Every year the world fails to act brings us closer to the tipping point when scientists fear that climate change may become irreversible.
"This is a terrible gamble with the future of the planet and with life itself."
It urged momentum at UN climate talks where countries are struggling over a pact to roll back greenhouse gas emissions and channel aid to climate-vulnerable poor nations.
The negotiations, scheduled to wrap up in Paris in December 2015, are supposed to align with a goal of limiting warming to two degrees Celsius (3.6 degrees Fahrenheit) over pre-industrial times—a target that scientists say will be hugely overshot on present trends.
"This is a decisive year," the Elders said, referring to a special summit in September called by UN Secretary General Ban Ki-moon aimed at easing some of the roadblocks in the talks.
The Elders said the road from 2015 should lead to a "carbon-neutral world" by 2050, meaning no more man-made carbon emissions would be added to Earth's atmosphere by mid-century.
"No one wants the generations to come to say that we failed them," they said.
Founded by Nelson Mandela in 2007 to promote peace and human rights, the Elders are chaired by former UN secretary general Kofi Annan.
Members include former US president Jimmy Carter, Nobel-winning South African prelate Desmond Tutu and former Algerian independence fighter-turned-mediator Lakhdar Brahimi.
Explore further: California beaches reopen after goo cleanup