I can understand why they're doing it. These sort of disruptions are the only way to draw attention to the issue.
It's the same with the Hong Kong protests. If they didn't do it then no one would know about the police brutality going on in HK.
They're raising an issue around climate change and about how big a problem it really is. Sure, they don't really understand it and neither does 99% of the population. I spent the last 5 years learning everything I can about climate change and I still don't understand that much of it. And yep, Australia only contributes 1.4% to the emissions locally (if you don't count the fact that Australian coal makes up over 30% of the global market but that's a much more complex discussion), but we also pollute more per capita than India and China. Like we pollute a ton more per person so we're telling developing countries that they should suffer more (or kill off their populations) so us and other countries don't have to be inconvenienced.
The point of the protests are to cause disruption to make people realise that there is a real issue. So the rest of the world may listen and the high total polluters (China, India and America) and the high per capita polluters (American, Australia and Russia) may start finding better ways to reduce emissions.
They're still annoying though.