Smith, the 21-year-old son of actors Will Smith and Jada Pinkett Smith, joined mass youth-led protests that took place in cities around the world in September imploring leaders to confront the climate crisis.

While climate activists such as 16-year-old Swedish student Greta Thunberg have targeted older generations for failing to act, Smith said involving adults was critical to tackling the threat posed by a warming planet.

"It's amazing the youth have got so involved. And they have to stay involved," Smith told the Thomson Reuters Foundation on the sidelines of the Web Summit technology conference in Portugal.

"But that bond (with parents) really matters," he noted, adding "Eventually, parents will see things have to change."

Smith, who co-starred with his father in the 2006 film The Pursuit of Happyness about an entrepreneur's struggle with homelessness, posts regularly on social media about water scarcity and global warming.

In September he urged his eight million Twitter followers to consider the environment and reduce their meat consumption.

Smith helped set up Just Water, a company that sells drinking water in bottles made mostly from paper and plant-based plastic, after spotting a discarded plastic bottle in the ocean while surfing as a teenager.

Read also: 'Never give up', Swedish teen tells Iowa climate activists after UN summit 'failure'

"Seeing the ocean polluted... sparked a journey into learning about the environment. I was like 'Wow, this is so groundbreaking.' I wanted to make an impact. I started learning about the environment, about plastic, about carbon dioxide."

Young people like Thunberg, anxious about the future of a hotter planet and angry at world leaders for failing to address the crisis, are rallying to fight climate change because they have the most to lose in future owing to their age.

Some parents have supported activist children as they skip school to protest. Smith, similarly, said his parents and teachers had played a "crucial role" in nurturing his passion for the environment.

A study by North Carolina University researchers published in May found that teenagers in the US coastal state who were schooled in the basics of man-made climate change saw their parents become more concerned about the issue.

Currently 37 of 50 US states plus Washington DC have adopted science education guidelines which include studying climate change as a result of human activity, according to Glenn Branch, the National Center for Science Education's deputy director.

Smith appears in a forthcoming feature-length documentary, Brave Blue World, which examines how technology can tackle rising water scarcity through tools like better waste management.

"Water is everything," he said. "It is such a special resource. We all have to care about it."

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