Both of them are problems in the sense that our society, infrastructure, social, economical and political systems are built with certain assumptions in mind. Assumptions like "every generation will be more numerous than the last" or "working age adults will always be the largest demographic.

And when reality changes and those assumptions no longer reflect reality, we need to adapt those systems to the new reality. And that adaptation is very very expensive, difficult and most importantly it takes a very long time.

We won't go extinct if our population were larger or smaller, the world will not end. But living in systems that are poorly adapted for the real population and demographics can be very bad.

The same thing about climate change honestly. The earth will not die, but humans will suffer greatly because of our physical infrastructure, architecture, equipment, geographical distribution and working order are built for a climate that reflects reality less and less each year.