WARNING: The following contains spoilers for Supergirl Season 6, Episode 6, "Welcome Back, Kara!," which aired Tuesday on The CW.
Supergirl Season 6, Episode 8, showed not just Kara returning from the Phantom Zone, but her estranged father, Zor-El. While he initially planned to travel to Argo City to see his beloved wife Alura, he tells Kara that he's changed his mind. At first, it's unclear where this sudden change of heart has come from, especially since he often told Kara that it was the memories of both her and her mother that kept him alive for so long in the Phantom Zone.
But, Zor-El soon reveals that his stalling to return to Alura has everything to do with his past guilt for letting the planet of Krypton die. And now, after learning that Earth's oceans are dying out, he wants Kara to help him save her new home from the same disastrous fate.
At first, Zor-El isn't entirely straightforward about his regrets. Initially, he tells Kara that he wants to spend some time on the planet of the yellow sun to see what her life has been like since she's lived on Earth. Zor-El even goes undercover -- with a delightful "glasses" disguise a la Clark Kent -- to accompany Kara to work at CatCo as her zany uncle. While he does his best to fit in, with the exception of lifting a copy machine with one hand in the air, it's clear that he's more interested in learning how these yellow sun-fueled superpowers could be of use to Earth. When J'onn calls upon Kara to help stop a satellite on its way to crash-land in National City, Zor-El tags along, excited to help his daughter on a mission.
In a charming scene, the two Kyptons easily blast away a satellite from hitting Earth. However, this mission leads them to discover an island made of trash in the middle of the ocean that quickly bursts into flames. After the duo puts out the fire, Zor-El cannot stop thinking about the trash and how it must be harming the ocean. He proceeds to run a test on all of the Earth's bodies of water and sadly discovers that Earth's oceans are dying. While the rest of the Super Friends aren't entirely shocked by this, having been aware of the Climate Crisis on Earth for some time, Zor-El is insistent that when Krypton started to die, its oceans went first.
Zor-El decides to upgrade Kelex, renaming him Oscar, and programming him to safely process/eat up the trash. He believes that this robot will then clean up all of the trash in Earth's oceans. While J'onn voices concern over Zor-El's seemingly too quickly made plan and exactly how his "upgrades" will work when mixing alien technology that shouldn't be mixed, Zor-El assures the team that his plan will work.
Spoiler: it does not work. Instead, it creates a kaiju-like trash monster that attacks them with a wide range of "upgraded" alien weapons. Although the team ultimately defeats Oscar and safely turns him back into Kelex again, everyone is shaken by the event. Then, Zor-El admits why he put off seeing his wife and any remaining Kryptonians: he was ashamed that he let their planet die by not investing in sustainable ways of life for their planet sooner. Similar to his behavior with Oscar, Zor-El admits that he tried to find quick fixes to environmental problems without really weighing the long-term consequences of messing with eco-systems.
Kara lovingly tells her father that she respects his ambition but that a problem like the Climate Crisis cannot be solved by one person. Echoing the heart of the entire series, Kara tells her father that it's through collective action on a global scale that will be what saves the planet from dying. It's the first time in Supergirl that the show broaches climate change, but its execution is one that reminds us all that we need to do our part to help the planet, and no one is exempt from that -- not even superheroes like Supergirl.
Supergirl airs Tuesdays at 9 p.m. ET/PT on The CW.