"Although adaptation is possible, historical shifts in climate have never occurred under conditions of such high human population numbers. Natural resources and ecosystems are already taxed and further climate perturbation is likely to be disruptive. Climate shifts in the past have frequently been accompanied by collapse of governments or extensive mortality. Increasing population pressure exacerbates the likelihood of pandemics and the destabilization of food-insecure regions can lead to failed states and threats to global security. Humans have survived numerous past changes in climate, but survival of the species is a poor measure of the true consequences and costs associated with adaptation to climate change."The threat of complete human extinction gets too much attention in some circles. There is plenty for us to be concerned about before we reach that stage - indeed, there are 6.8 billion reasons for concern prior to getting that far.
And it is worth repeating the point that humanity has never faced a situation quite like this before; the threats are on an unprecedented scale. We have never had anywhere near this many people, with anywhere near this amount of infrastructure investments to protect, with anywhere near this level of consumption, with anywhere near this level of firepower to hurt ourselves if things turn pear-shaped geopolitically. Climate change is far from the only issue we face, but it is a threat multiplier in a world already under incredible and growing stresses. We are living in a historically novel period for all kinds of reasons and the stakes are higher than they have ever been.