I think its pretty simple; with climate change and pollution comes environmental collapse and starvation. Clean water, food and other ressources will become even harder to obtain. Desperate people will be more likely to turn to exremism and civil unrest will increase. Our politicians know this and are trying to get into a position where they can stay in power and not be eaten. Obviously with hindsight it would probably have been better for everyone involved if we had taken the necessary steps to protect our climate and ecosystems a few centuries ago, but that doesnt get you elected and doesnt matter to you if you are going to rule just for the next 5 years or so.