>2. What is the point of studying science, if politicians do not listen to science?
That's not really what's happening.
From day one, in the eighties, the ones who have been vocal about this have been politicians. Al Gore, the IPCC, etc. I mean, most people can't name a single scientist advocating this issue. In France, just like in the US, the number one advocate on this issue is a TV show host. And in fact, the most well-known French scientist (turned politician) who talked about global warming (Claude Allegre) is what people would call a skeptic or denier...
What's happening today is that:
1. in western democracies, people predominantly vote to ignore it
2. in developing countries, leaders also choose to ignore it
Greta is protesting against point 1. That's not going to achieve much more. At this point, people have made their mind about the issue and I don't think the balance is going to be tipped significantly. I don't even understand what she's trying to achieve. She can shout at politicians as much as she wants, ultimately the power is held by the people of those democracies.