A whole lot of food needs to be pollinated by insects. Those insects have a time when they get out of their eggs in spring. But what if the tree blossoms before the insects are here? No pollination. This means it dies a blossom, never to be turned into food. Continue this for some years and the insects die out, some more and the final plant will die.
It’s always happened, yes, but it’s too fast.
The people will die, the planet recovers.
And what’s a planet if there’s no people to enjoy it.