The broadcast isn’t a call to action. It’s a warning to the world. That’s it.
“Hey guys, there’s a chance a mass extinction event is occurring in your lifetime, please prepare. Here’s the reason I believe it’s occurring. Here’s the proof that it’s man made, and has happened before and how this is possible.”
He’s not telling random civilians to stand up and fight; he’s just trying to give people warning so they can try and survive the sinking of the world. It’s likely Oda taking inspiration from the story of Noah where he would travel and warn everyone to prepare for the imminent flood, but those he warned would laugh at him like people are doing to Punk now.