I hope you realise that these posters are not necessarily entirely factual. They are just trying to get people to actually do something about climate change and make a difference, because telling someone calmly and gently is not the way to express urgency. We've had the time to do that, and it didn't get through to people.
People need to understand that crises like Brexit and climate change aren't going to be solved by being idle. People go about, acting as if life is just business as usual, but (to an extent), life is not business as usual, because there are threats to our longevity as a race that will remain threats unless we take action and try to solve them. Maybe if people are scared, they will be more inclined to actually take action than to just let the words wash over them and carry on.