Greta Thunberg is a 16 year-old girl who has become worldwide famous for her campaings to raise awareness against climate change and other environmental issues. She is very articulate in English and an excellent communicator.
Above, you can watch the emotional speech that she gave at the Climate Summit at the UN, which she reads slowly and clearly, but has no subtitles (C1) and below, you can see an interview on the Daily Show where her discourse becomes more natural and colloquial, even humorous at times, which can be accessible to B2 students.