It's hyperbolic but there is value in its core - ecosystem collapse would bring us close. And the point below is not unreasonable - our collective response to 1.5 vs 4.5 degrees warming will not be linear. Mass migration, resulting fascism, resource wars and mismanagement, evaporation and starvation could finish those who remain.

If we're forced to live a completely different lifestyle it may be tantamount to the extinction of modern humanity.