I'm agnostic about the requirements for addressing COP25. I assume the organizers and attendees know what criteria makes sense for them.
I'm trying to relate her attendance back to the arguments offered in this thread for her attendance: That she knows something the other attendees don't, and that her message to them would be more effective if delivered in person.
As to whether she knows better than the other attendees: I'm skeptical. The primary audience at COP25 appears to be policy makers and subject matter experts. Call them the diplomats and the scientists.
I doubt she knows more than the scientists attending COP25. Her message is that she's listening to the scientists, and so should the rest of us. Surely the scientists attending COP25 are listening to themselves, and each other. If one of them is ignorant of something, they have other scientits in attendance to set them straight via personal encounter. The scientists probably don't need Greta at COP25.
What about the diplomats, the policy makers? Does Greta know things about policy that they don't? The whole point of COP25 is to get diplomats and scientists together. Even if Greta has policy ideas that haven't occurred to the diplomats, she got them from the scientists. If the diplomats aren't listening to those same scientists that they're going to COP25 specifically to talk to in person, why would they listen to Greta?
Given that Greta's main source of science and policy information seems to be the same people and organizations that put on and attend the COP conferences, why does Greta need to go there and talk to them at all?
I'm skeptical that anyone attending COP25 doesn't already know everything Greta knows, if not more.
I'm skeptical that anyone attending COP25 who doesn't already know what Greta knows, needs to hear it from Greta as opposed any of the other diplomats and scientists also attending COP25.
And I'm skeptical that anyone attending COP25 who wasn't already sympathetic to Greta's message, will be more sympathetic if they get it from her in person. Assuming anyone like that exists. And that Greta can get to them at the conference. And that they'll agree to listen to her talk to them.
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My theory is that Greta's attendance at COP25 isn't about telling anyone there anything they don't already know. I think it is about meeting people in person, but not to try to persuade them.
I think the message is flowing out from COP25, not into it via Greta. Rather, Greta's attendance lends cachet to the proceedings. Schoolchildren who believe in Greta will see her at COP25, and believe in COP25 by extension. They'll see her with the various diplomats and scientists, and believe in those diplomats and scientists. It's good PR. It reinforces the general appeal to let the UN take charge of fighting global climate.
That's my theory, anyway. I think it's much more plausible than the theory that she has an important message for the diplomats and scientists attending COP25, and it she has to deliver it in person.