'Accelerated action needed to avert global warming'
Ban Ki-moon says national emissions pledges from more than 180 nations are a good start.
JOHANNESBURG - United Nations Chief Ban Ki-moon has called on world leaders at the start of two weeks of climate talks in Paris to accelerate action to avert a dangerous rise in temperatures.
He says national emissions pledges from more than 180 nations are a good start, but aren't enough to curb global warming at the two degrees Celsius limit scientists say can prevent the worst consequences.
He adds Paris must mark a decisive turning point.
"A political momentum like this may not come again. But neither have we encountered as such a great opportunity at this time; you have the power to secure the wellbeing of this and succeeding generations."
US President Barack Obama also addressed the COP21 climate change conference in Paris, telling delegates that cynicism is the greatest enemy at the meeting.
He says long term strategies must be found.
"Here in Paris let's secure an agreement that builds in ambitions and where progress paves the way for regularly updated targets, targets that are not set for each of us but by each of us, taking into account the differences that each nation is facing."
Obama says America has accepted its responsibility as the world's second biggest greenhouse gas emitter to help fix climate change, adding that global action need not damage economic growth.
He says a growing threat of climate change could define the contours of this century more dramatically than any other.
The US president has echoed his French counterpart Francois Hollande and Ban in calling for decisive action and a lasting solution.
"The defiance that proves nothing will deter us from building the future we want for our children. What greater rejection of those who tear down our world, than marshalling our best efforts to save it. The declaration that for all the challenges we face, the growing threat of climate change could define the contours of this century more dramatically than any other."
CNN's Jim Acosta reported that, "These leaders, we should point out, are in pursuit of a large climate agreement that will commit nearly every country on earth to big reductions and carbon emissions over the next couple of decades. Scientists are sure there will be enough to avert the most severe effects of global warming."
Earlier, President Hollande warned the fight against terrorism could not be separated from the fight against global warning.
Hollande warned delegates that 'good will and statements' of intent are not enough because humanity is now at breaking point.
"Paris must be the start of a deep change. We can no longer consider nature as a vulgar and inexhaustible source destined for our own accomplishments."
Just two weeks ago Paris was rocked by coordinated terror attacks carried out by Isis.
Accompanied by Hollande, Obama earlier laid a single white rose at the place where 90 of the 130 victims were killed.
Security has been stepped up significantly this week, where 150 world leaders are attending the conference.
Terror analyst Jean-Charles Brisard said, "It's a unique moment and a unique opportunity, not only to show unity and solidarity, but also to try to build up a coalition against Isis in Syria. So this is important because we have all the heads of states here in Paris."