A lot of climate change experts claim that it is an "existential threat."
Why do some people call climate change an “existential threat”? | MIT Climate Portal
“There is a genuine possibility that within the coming century, we will hit temperatures that are deeply incompatible
with the continued existence of human life."
If the experts truly thought that climate change would cause the end of human life, I wouldn't think that they would fly around the world in private jets to attend climate change conferences.
Even if I thought that the modern world - gas cars, gas furnaces, air conditioning - would kill everyone, I am not sure that most people would want to go back to a 19th century life style.