The Hollywood star and former California governor said he despairs of what Trump's energy policy, which is heavy on fossil fuels, will do to the planet.
"When I hear he wants to bring coal back, that's going backwards. The next thing he'll want to bring horses and buggies (carts) back," the actor and activist told reporters at the Cannes film festival.
"Trump or no Trump we all have to move forward," he added.
And he urged people worldwide to rise up to save the planet.
"All great movements -- civil rights, the vote for women, the anti-apartheid movement, the freedom movement in India -- all started on a grassroots level.
"We cannot wait for Washington. The people have to rise up and say we got to protect what we have so we don't have climate change and seven million people dying every year because of pollution."
Schwarzenegger narrates a new documentary by the son of undersea explorer Jacques Cousteau, "Wonders of the Sea 3D", which he claimed would make "people fall in love with the ocean".
Environmental shaming
He said its positive message worked much better than "the shaming, guilt and finger pointing" that Schwarzenegger believes puts people off environmentalism.
"You can't just tell people all the time you should turn off your jacuzzi and not drive a big car," he told the Hollywood Reporter.
"If you want people to change you got to make people feel good. Like 'Come to the gym and you will feel so much better.' When you see this film you will inevitably fall in love with the ocean," he added.
Even though Schwarzenegger is also a Republican, he has had prickly relations both politically and personally with Trump.
In January, Trump blamed the low ratings of "The Apprentice" television show on Schwarzenegger, who took over from Trump as presenter.
Schwarzenegger said in March that he was quitting the show because it had too much "baggage".
He said Trump's name in the credits as executive producer scared away sponsors and viewers.
While in Cannes, Schwarzenegger also congratulated French voters on electing the centrist Emmanuel Macron president earlier this month.
Trump had praised his opponent, far-right leader Marine Le Pen.
"I love being in France," he told Screen International, adding the French people had done "a great job with the election of the president".
The "Terminator" star is also playing the world's greatest hitman in a forthcoming film being sold at Cannes, "Why We're Killing Gunther" by "Saturday Night Live" performer Taran Killam.
The action-comedy follows a group of assassins on a mission to kill Gunther, the world's greatest assassin.
Schwarzenegger also confirmed he would be making a sequel to "Twins" with Danny DeVito and Eddie Murphy, called "Triplets" and that he would be returning to the "Terminator" franchise.
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