A South African who battled apartheid as a teen, then went on to lead global campaigns to end poverty and protect human rights took over on Monday as the new international head of the environmental group Greenpeace.

Kumi Naidoo, Greenpeace International’s new executive director, said climate change makes his new job a logical addition to his resume.

“If the whole planet is under threat ... what’s the point of not addressing that and saying we’ll do other development work?” he said in an exclusive interview with The Associated Press on Thursday.

Mr. Naidoo, 44, has fought for the rights of women and children, among the most vulnerable when droughts bring hunger or floods disrupt livelihoods. He has pushed to strengthen international cooperation and has ensured the concerns of poor countries are heard when rich nations plan the future.

Greenpeace will be there when negotiators sit down next month in Copenhagen to try to draft an agreement to cut the greenhouse gas emissions blamed for global warming.

“We either get it right and all of humanity comes out on the other side with a new world,” Mr. Naidoo said of climate negotiations. “Or we get it wrong and all the world is going to sink.”

World leaders said on Sunday it was unrealistic to expect an international, legally binding agreement to emerge from Copenhagen, something for which Mr. Naidoo had hoped. Instead, the goal is a political framework, with a fully binding legal agreement left to a second meeting next year in Mexico City.

“Anything short of a binding treaty in Copenhagen must be read as a failure of leadership on the part of the political class,” he said on Monday. “We can’t change the science. The science is clear. We have to change the politics. If we can’t change the politics, then we have to put our energies into changing the politicians.”

Gerd Leipold, whom Mr. Naidoo is replacing at Greenpeace, said his successor represents a watershed for the organization founded in the 1970s by Americans campaigning against U.S. nuclear tests.

Mr. Naidoo is the first African to head Greenpeace, and the first to come from outside the organization, said Mr. Leipold, a German who once headed Greenpeace’s nuclear disarmament campaign.

Poor nations, particularly in Africa, are expected to be hardest hit by climate change, though they have contributed little to the pollution that created the phenomenon. Mr. Naidoo is among those who argue that industrialized nations that got rich off dirty technology not only need to change their ways, but pay to help developing nations cope with the severe weather associated with climate change and to get access to clean energy to fuel their rise from poverty.