The 95-year-old documentary maker, who was announced at Monday’s ceremonial opening as the “people’s advocate,” spoke ahead of presidents and prime ministers from more than 100 countries.
He said for much of humanity’s existence, the climate on Earth had swung wildly before stabilising 10,000 years ago, allowing human civilisations to flourish.
“The stability we all depend on is breaking,” he said.
Sir David said the action necessary to curb greenhouse gas emissions to levels that would prevent dangerous global warming was possible, if countries move quickly and decisively.
“We are, after all, the greatest problem solvers to have ever existed on Earth,” he said.
“If working apart, we are a force powerful enough to destabilise our planet. Surely working together, we are powerful enough to save it.”
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The broadcaster warned against short-sightedness, asking leaders how they might explain to a child that “the smartest species” on the planet failed to see the bigger picture “in pursuit of short-term goals.”
He added that the answer to the climate crisis needed to be equitable, saying that “those who have done the least to cause this problem are being the hardest hit.”
The conference had the chance “to rewrite our story to turn this tragedy into a triumph.”
“We are all the greatest problem solvers to have ever existed on Earth,” Sir David said.
“Our motivation should not be fear but hope.”
British Prime Minister Boris Johnson earlier opened the summit by saying the world was strapped to a “doomsday device” and future generations “will not forgive us” if major changes are not made.