Because the climate IS changing, and the effects are already noticeable, and they will get worse.
Like to eat chocolate? Bananas? Foods pollinated by bees? Concerned about what would happen if much of the Indian subcontinent ran out of fresh water and its population becomes pushed to emigrate? (And before that, the floods as those Himalayan glaciers release their stored water at an unpredictable but increasing rate?) Know anyone who has to buy homeowners' insurance in Florida, or another subtropical area? Concerned about Dengue and West Nile Virus moving north into new territory?
If the answer to any of those questions is YES, then you care about climate change.