Drone footage revealed group of leopard seals taking turns to rip bits of flesh from a penguin carcass.
Attenborough said he was encouraged by the action of young people around the world who are publicly fighting for climate justice.
"In the 20 years since I first started talking about the impact of climate change on our world, conditions have changed far faster than I ever imagined," the British naturalist and broadcaster says.
"The continuation of civilizations and the natural world upon which we depend is in your hands," Attenborough told leaders.
Trump's decision to withdraw the U.S. from the Paris climate agreement was widely condemned.
Was this ancient creature done in by one of its own kind?
The footage on the BBC wildlife show made headlines this week.
The 89-year-old will get back behind the mic to narrate the BBC's upcoming 'Planet Earth' sequel.
The species has eight eyespots to scare away predators.