Why has there not been a Hollywood movie that seriously tackles climate change?
Spotlight (2015) star Mark Ruffalo, one of Tinseltown's most ardent environmental activists, thinks it is because the issue has not reached a cultural tipping point.
But it is only a matter of time, says the 48-year-old, who also believes celebrity activists such as himself and Oscar-winner Leonardo DiCaprio have also been growing more vocal about such issues despite efforts to silence them.
Speaking to The Straits Times in New York, where he was promoting the magic caper Now You See Me 2, Ruffalo - a respected dramatic actor and star of films such as last year's Best Picture Oscar winner Spotlight, reveals that there are not many movie scripts about climate change despite it being a hot-button topic.
"There hasn't been one yet like The Kids Are All Right was to gay marriage or Spotlight to journalism," he says of two of his best-known films.
Spotlight, about the Boston Globe newspaper's expose on the cover-up of child molestation in the local Catholic Church, earned Ruffalo a nomination for Best Supporting Actor. Also acclaimed was The Kids Are All Right (2010), a movie about a lesbian couple whose child seeks out his biological father, which netted him a nomination in the same category.
"But I also think that those kinds of movies, they don't just come out on their own - the culture's got to be ready for it. We have to be at the fever pitch of a conversation and then, boom, they sort of happen. I don't think we're quite there yet with the conversation on climate change, although it's starting to break free a little bit now."
The star himself, who also played the Hulk/Bruce Banner in The Avengers (2012) and Avengers: Age Of Ultron (2015), has not always been so passionate about such causes.
This changed when gas companies began looking into fracking - a controversial method of extracting gas and oil from shale rock - on his family's land in New York state eight years ago, prompting him to look into the risks involved, and become the first celebrity spokesman for the anti-fracking movement in the United States.
He speaks out on this and other causes because of his three children, aged eight to 15, with his wife actress Sunrise Coigney, 43.
"And then I was living in a place where they were going to do hydro-fracking. I could have left, I could've just protected that one area - they offered to just take that one area off the table and do everywhere else.
"But then your morality comes into question - who are you as a person, what are your beliefs and do your beliefs line up with your actions."
He eventually realised he had to speak up. "I wanted to run away from activism - that was my first reaction. But then I just didn't feel good about myself. I catch s*** from people, but I also don't think what I'm saying is that extreme. Most people agree with it," says Ruffalo - although he has also espoused certain fringe beliefs, including conspiracy theories about the real culprits behind the Sept 11, 2001 terror attacks and the current Zika virus outbreak.
He says the activism has also made him a better actor "because it brings me closer to people's struggles and what is great storytelling other than exploring one struggle or another? And what is a great actor or artist other than someone who knows what's happening in the time that they're living and knows it in a really experiential way?"
Being thrown into the middle of a conflict over such issues "is where the growth is - as an artist, as a human being, as a citizen."
Ruffalo believes his career has so far not suffered from his activism, although he jokes that maybe it is why the Hulk was not included in Marvel's latest film, Captain America: Civil War (2016). "That's the beginning."
Maybe a career backlash will happen at some point, but "I'd have to be incredibly unpopular for people to decide to stop watching the movies I'm in. That's all they care about at the end of the day in Hollywood - ticket sales".
And while certain celebrity activists have been criticised for their stances, he thinks it does help a cause if more famous people are on board.
"DiCaprio's reach in the world is greater than any politician when you look at the social media reach he has compared to the United Nations or The New York Times."
But he adds that there has been a sustained effort to smear artists over the years. "Starting after the Vietnam War (which ended in 1975), there has been a concerted effort to discredit artists as scumbags, as morally impaired, as being unreliable or having no credibility.
"But people are breaking free of that now, they're starting with baby steps, but I see it everywhere, actors are becoming much more socially involved.
"Once artists find their voice, they have the credibility, they're not beholden to any interests. I think people are becoming emboldened."