Anything that's skin-deep is shallow or superficial. Your skin-deep commitment to saving the environment isn't terribly serious.
You may have heard the saying "beauty is only skin-deep," which means that while someone may be beautiful on the outside, their character—what's inside, and more meaningful—isn't necessarily attractive. The first attested use of skin-deep was in "A Wife," a 1613 poem by Sir Thomas Overbury: "All the carnall beauty of my wife, Is but skin-deep." Its publication infamously resulted in Overbury's murder when its subject deduced that it was about her.