Peter Gabriel, “io.”

A small subset of British prog rockers from the 1960s and ’70s lost their hair and wound up puttering about in their gardens. The list includes Brian Eno, Ian Anderson and now, Peter Gabriel (Yes’ Jon Anderson retains a wonderfully coifed mane!). Like a fine wine, these artists mellow with age, and like a raging party, the laws of thermodynamics demand they eventually chill out. At which point they release music to putter in the garden to.

While the music is mellower, the message is more urgent.

Former Genesis lead singer Peter Gabriel’s latest, i/o, will have you thinking some big thoughts while you’re out there among the azaleas. The album, his first studio long-player in more than two decades, tackles issues from global warming to our faltering psyches from a perspective that’s equal parts pessimist and visionary. It comes in multiple mixes highlighting the work of producers Mark “Spike” Stent (“Bright-Side Mix”), Tchad Blake  (“Dark-Side Mix”) and Hans-Martin Buff (“In-Side Mix”). The album shares its name with one of Jupiter’s moons and Gabriel has released several songs on various full moons.

Opener “Panopticom” appears to be a riff on Michel Foucault’s metaphor for disciplinary power structures, the panopticon. During Gabriel’s fairly extensive introduction to the song during a recent concert in San Francisco, it seemed Gabriel’s take involved wiring up nature into a giant wifi network.

“In the air, the smoke cloud takes its form/ All the phones take pictures while it’s warm,” he sings. “Panopticom, let’s find out what’s going on/ … where clues are leading/ … won’t you show us what’s going on?/ … so how much is real?”

The song’s anthemic chorus could’ve been souped up with horns and electric funk, a la Gabriel’s other big solo hits, “Big Time” and “Sledgehammer,” but instead the mood is muted. The vibe is sort of akin to trying not to make too much of a racket and rouse your mum as keyboards and synthesized sonic washes punctuate the groove.

The somber piano and heartfelt vocal melody of “Playing For Time” feels a bit like a Randy Newman number on a Pixar film soundtrack.

“Oh, oh the moments come and go/ While the memories ebb and flow/ Play again, play again,” Gabriel muses. “Oh, there’s a hill that we must climb/ Climb toward these mists of time/ It’s all in here what we’ve been through.”

Gabriel is joined by none other than Brian Eno on the synth-heavy “Road to Joy,” which feels a lot like the seasick and slinky groove from David Bowie’s 1975 hit “Fame.” “Olive Tree” exudes ’80s pop joie de vivre via handclaps and velvety synths. The song’s upbeat musical stabs are eerily similar to some half-forgotten song from that decade that I’ve just spent far too long trying to recall to my brain.

On the album’s closing track, “Live and Let Live,” Gabriel waxes psychoanalytical over a heartwarming groove, perfect for the decision-making montage in a Hallmark movie: “Just how much does it have to hurt/ Before you let go of the pain?/ Just how deep does it have to be/ Before you yearn to be free again?/ Everyone can lock you away/ Or, you can choose to remain /Every day can pass you by/ While you were holding the key.”

Listeners expecting the high-energy Peter Gabriel that dominated MTV in the mid-’80s may be surprised by how much he’s mellowed in the intervening years. But anybody old enough to remember the psychedelic claymation of the “Sledgehammer” video from their youth has more than likely slowed their pace a bit as well, and maybe even discovered the joys of tending their gardens. And now they have another album as a soundtrack for their pensive puttering.