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Tom Jamieson

She has worked in Thailand, Laos, Nepal, and elsewhere on the social impacts of deforestation, landscape restoration, and climate mitigation. Sato, 25, is from suburban Tokyo but now studies in the U.K. “Climate change is not just an issue related to the environment,” she says. “It exacerbates social exclusion, conflict, classism, racism. We all have to take part in climate justice.”

After capturing the world’s attention at the United Nations in New York City last September, Greta Thunberg, now 17, spoke in December at the UN’s climate change conference in Madrid. Her main theme: science. “I’ve given many speeches and learned that when you talk in public, you should start with something personal or emotional to get everyone’s attention,” she said. “But today I will not do that because then those phrases are all that people focus on. They don’t remember the facts, the very reason why I say those things in the first place.”

Rosie Mills, 19, led a petition drive that persuaded the local council in Lancaster, England, to declare a “climate emergency” after catastrophic flooding. Last year she ran for a seat in the European Parliament as a Green Party candidate. She lost, but didn’t finish last. “One of the weirdest things is when a teacher comes up to you and says, ‘I’m going to vote for you.’ Then she assigned me an essay the next day.”

On a school assignment in Rwanda, Irakoze, 20, came upon an overflowing landfill in his hometown. He learned that discarded electronics create more than 50 million tonnes of waste globally each year. Now a university student, he founded Wastezon, which uses a mobile phone app to connect consumers with recycling industries. The company has helped send 460 tons of electronics to recyclers in Kigali, Rwanda’s capital.