A filmmaker creates an imaginary letter to his daughter in dreaming of a world where best current practices and technology are applied to solve climate change in “2040,” an almost tearfully optimistic take on a subject that has long lived on “gloom and doom.”

Aussie Damon Gameau (“That Sugar Film”) and wife Zoe plant a tree with his then-four-year-old daughter Velvet, and then take us to visit legions of school children from much of the world, listening to their concerns. Then Gameau takes us to experts and academics, and hands-on engineers of soil, power, ocean and planet “regeneration” to see how things might be for 24 year-old Velvet (Eva Lazarro).

We hear another version of the economic/environmental “donut” theory of how to rethink the global economy to make it more planet-friendly and equitable from Cambridge economist Kate Raworth.

We’re shown what can be achieved by decentralizing the economy and the power grid with the “bottom up” solar home microgrids of Bangladesh, where villages without power have been brought into a healthier, more stable 21st century by adapting solar-roof/battery setups that have revolutionized life for the better.

Gameau hangs with Paul Hawken of Project Drawdown to learn how vital rethinking agricultural practices (killing “Big Ag”) to improve farm practices, soil regeneration and reap the rewards of carbon sequestering that come with that.

Gameau goes to see where near-futurists envision offshore kelp farms that start the process of healing the oceans as they create whole new sectors in a post-fossil fuel economy.

And we hear one other “Big Vision” idea that “We need to have now” — the global empowerment of girls and young women. Education, sexual independence (freed from forced marriages and pregnancies) and adding millions of great minds to throw at the world’s problems might be the single most important thing we can do about climate change.

Illustrated with digital effects and whimsical stop-motion animation, “2040” is the opposite of the decades of documentaries built on the dire warnings about the future that is already here — climate disasters on the rise with rising temperatures, rising sea levels, mass extinctions and spreading droughts.

And it’s more upbeat and less cynical than the cautionary “Planet of the Humans,” pulled from Youtube for attacking the less-than-stellar record of those in the forefront of the environmental movement, misguided champions of “biomass” fuels and the like.

Gameau takes it as a given that things have to be done, and now, and that we’ll do them. Maybe that’s as naive as leaving the short-sightedness of human greed out of his film’s calculations. The swipes at Big Ag, Big Fossil and Big Banks aren’t going to be enough to break their stranglehold on this century.

But in showing us the upside of turning a deaf ear to those with the money to amplify their self-interested voices of doubt, Gameau and “2040” give us the tiniest of hopes that maybe things will get better soon enough for us to escape the very worst.

MPAA Rating: unrated

Cast: Damon Gameau , Zoe Gameau, Velvet Gameau, Eva Lazarro, Helena Norberg-Hodge, Kate Raworth, Paul Hawken, Colin Seis, many others

Credits: Written and directed by Damon Gameau. A Together Films release.

Running time:1:31