Jake's progress

These days, transforming an indie kid into a Hollywood hero would seem an almost annual Tinseltown tradition. Think Heath Ledger with

Not that you'd know it from meeting him in a Santa Monica beachside hotel. Hardly dressed for success (frayed jeans, scuffed boots, a motheaten long-sleeved T-shirt), he is so laid-back, he's practically flat-out. 'I'm expecting whatever is supposed to happen,' he drawls, full of West Coast lethargy. 'I'm comfortable with whatever that is. I feel OK, I'm excited. There's only so much that someone who has been through it can tell you.'

He can only be referring to his girlfriend of the past year, Spider-Man starlet, Kirsten Dunst. He certainly doesn't mean his actress sister Maggie, who played Cupid between the two after working with Dunst on Mona Lisa Smile. 'She doesn't know what a Hollywood movie is,' Gyllenhaal scoffs, gleeful of the chance to get one over on his sibling. Yet, as one half of Hollywood's cutest power-couple - evidenced by the promise ring he's wearing - Gyllenhaal is quick to dismiss the notion that it was Dunst who influenced his step up to stardom. 'I did this movie before I met Kirsten,' he retorts, when the subject is broached, sounding weary and wary of media interest in his personal life. When asked how he copes with this, he shoots back, 'A lot of ice and a lot of painkillers.' The reason Gyllenhaal has landed himself the biggest payday of his career is his politics. One of an increasing number of Hollywood youngsters using their fame to trumpet green causes, he was immediately attracted to a film --in which he plays the son of Dennis Quaid's climatologist - that seemed to be on his wavelength. 'I try to say things with what I do,' he says. 'I don't think this film will have people protesting, like they did with The Passion Of The Christ, but it does raise issues. They're issues we all know about, and take for granted. Hopefully, it'll scare the shit out of some people.'

Growing up in LA, Gyllenhaal was taught to recycle in school, though he admits, 'I don't think I was ever really conscious of the ramifications of what I did on the environment, or, more importantly, what corporations in the world have done.' These days he sidelines a portion of his income to plant trees in a forest in Mozambique to offset the carbon dioxide he puts into the atmosphere. 'It would probably be better to buy a hybrid car rather than plant trees, but I'm trying to do my bit.' Also an avid supporter of the Rock The Vote campaign, which encourages youngsters to head to the ballot boxes, Gyllenhaal comes across as a committed individual, while managing not to sound self-righteous.

This 'old head on young shoulders' vibe no doubt stems from his childhood. Godson to Jamie Lee Curtis and Paul Newman - who gave him his first driving lesson when he was 15, by throwing him behind the wheel of a racing car - his upbringing virtually assured his entry into the arts. His father, Stephen Gyllenhaal, directed such acclaimed films A Dangerous Woman (featuring Debra Winger, and Jake in a small early role). His mother, Naomi Foner, is a screenwriter, Oscar-nominated for Running On Empty, which starred the late River Phoenix. 'I've been on my parents' sets since I was little,' he says. 'And they have always been people that I've looked up to. They've always supported me, and probably will support me in whatever I do.'

That said, aside from a brief role as Billy Crystal's son in City Slickers in 1991, Gyllenhaal wasn't allowed to take a lead role until he played a teenager obsessed with rocket science in the saccharine 1999 effort, October Sky. At the time, rather than follow it with more roles, he followed his sister to Columbia University, to study Eastern religions on a course presided over by Professor Robert Thurman (Uma's father). In the year Maggie graduated, he dropped out. 'I had gone to school to be intellectual and cerebral,' he says, 'but I'm happier when I'm acting. I don't want to be seen as an icon for college drop-outs.'

While he may avoid this, Gyllenhaal is already a poster boy for angst-ridden, disenfranchised teens, thanks to his impressive recent CV. The youthful object of affection for Jennifer Aniston and Catherine Keener in, respectively, The Good Girl and Lovely & Amazing, he played a grief-stricken teen in Moonlight Mile and a schoolboy who stops taking the pills in Donnie Darko before taking an acclaimed West End stage role in Kenneth Lonergan's This Is Our Youth last year. 'I played a lot of characters that had a lot of similarities to them, because that was what I was going through,' he notes, though his sunny demeanour today would suggest his teenage troubles were, at best, growing pains.

Although he declined a role in Bernardo Bertolucci's controversial love-triangle, The Dreamers, reputedly because of the nudity, Gyllenhaal's not about to give up on the indie scene. Set to star in Ang Lee's gay cowboy drama Brokeback Mountain, opposite Heath Ledger, he has already wrapped an adaptation of Broadway smash Proof, alongside Gwyneth Paltrowand Sir Anthony Hopkins. Busy he may be, but is he happy? He admits he is. 'It feels odd for me to say that, especially as I don't think I've ever played a role that would reflect that,' he says. Until now, that is.

The Day After Tomorrow opens Fri 28 May.