Every organism and ecosystem you’ve ever encountered in your life is adapted to an Ice Age climate, but we’ve recreated the conditions of a Hot House earth. Species and ecosystems adapt on much slower time scales. They cannot adapt to changes this abrupt, which means they will necessarily collapse if we do nothing and allow emit CO2. Every other time in earths history that the CO2 levels have rapidly risen it’s lead to a mass extinction. Yes it’s been hotter before but that change happened gradually. It’s like the joke about poison vs medicine, it’s the dose that kills you.