David Attenborough warned world leaders at a climate summit we are "already in trouble" but "our motivation must not be fear but hope" for change.
Speaking during the opening ceremony of Cop26 in Glasgow, he said young people can "give us the impetus we need to rewrite our story" and turn the tragedy of climate change into triumph.
The climate campaigner charted carbon emissions throughout human history, which has peaked at 414 parts per million.
"Our burning of fossil fuels, our destruction of nature, our approach to industry, construction and learning, our releasing carbon into the atmosphere - we are already in trouble," he said.
"The stability that we all depend on is breaking. This story is one of inequality as well as instability.
"Today those who have done the least to cause this problem are being the hardest hit - ultimately all of us will feel the impacts, some of which are now unavoidable."
US president Joe Biden gave a standing ovation to Sir David following his speech.
The naturalist and broadcaster told the summit that those who have done the least to cause the problem are being the hardest hit.
He asked: "Is this how our story is due to end - a tale of the smartest species doomed by that all too human characteristic of failing to see the bigger picture in pursuit of short-term goals?"
He added: "Perhaps the fact that the people affected by climate change are no longer some imagined future generations but young people alive today, perhaps that will give us the impetus we need to rewrite our story, to turn this tragedy into a triumph."
He added that "we are after all the greatest problem solvers to have ever existed on earth" and that we "now understand the problem" of how to put climate change into reverse.
Sir David told the climate summit the motivation for tackling climate change should "not be fear, but hope".
He said: "It comes down to this. The people alive now or the generation to come will look at this conference and consider one thing - did that number stop rising and start to drop as a result to drop as a result of commitments made here.
"There's every reason to believe that the answer can be yes.
"If, working apart, we are a force powerful enough to destabilise our planet, surely working together we are powerful enough to to save it."
He told delegates: "In my lifetime I've witnessed a terrible decline. In yours, you could and should witness a wonderful recovery. That desperate hope... is why the world is looking to you and why you are here."
Boris Johnson today opened COP26 with a desperate plea to humanity to “defuse the bomb” of climate change as he spoke to 120 world leaders.
Cop26 must mark the beginning of the end of climate change, Boris Johnson has said.
Addressing the opening of the Cop26 summit in Glasgow, the Prime Minster said: "If summits alone solve climate change then we wouldn't have needed 25 previous Cop summits to get where we are today. But while Cop26 will not be the end of climate change it can and it must mark the beginning of the end."
He added: "In the years since Paris the world has slowly and with great effort and pain built a lifeboat for humanity and now is the time to give that lifeboat a mighty shove into the water like some great liner rolling down the slipways of the Clyde.
"Take a sexton sighting on 1.5 degrees and set off on a journey to a cleaner greener future."
The Prince of Wales also addressed world leaders at the Cop26 global climate summit in Glasgow.
He said: "The Covid-19 pandemic has shown us just how devastating a global cross-border threat can be.
"Climate change and biodiversity loss are no different - in fact, they pose an even greater existential threat, to the extent that we have to put ourselves on what might be called a war-like footing."
Charles told the leaders the "eyes and hopes of the world" are on them to act fast because "time has quite literally run out".
