It's a little depressing to see that before Greta Thunberg, all the way back in 1992, the UN had another child of a similar age speak to them on very similar environmental and climatological topics.
Severn Cullis-Suzuki:
https://peertube.social/videos/watch/14f948d1-ed4e-489f-bbb1-77bb6d0f8b9b
Greta Thunberg:
https://peertube.social/videos/watch/ecdfd979-ab84-4d6a-a3b1-2eb082fc5082?start=9s