I think that total ecosystem collapse and the extinction of wildlife is a possible scenario this century (perhaps even likely, if we continue with business as usual rather than addressing the climate crisis).
Followed by the death of everything that depends on birds and insects, which is probably a large percentage of the remaining wildlife. Similar extinction scenarios are plausible with ocean life.
I guarantee that this would result in the collapse of civilization if it were to occur.
This is one reason it's absolutely vital to halt greenhouse gas emissions. Loss of habitat and pesticides are also huge problems for insects and other wildlife, so dealing with global heating is necessary but perhaps not sufficient to save them, but we have a clear deadline for when we must reach carbon neutrality, so that seems like the top priority.
I think that the decrease in biodiversity is dangerous, but not threatening an extinction event yet - or at least I've never seen a credible scientist who works in that field making that claim.
(I'd also note that both of these things seem to be caused primarily by pesticide usage and other agricultural practices, not climate change)
I once saw the Monarch migration. I can try to describe it but I can't
tell you what it was like. Maybe if I was a poet. Can you feel it if I
say "1/m^3"? I was within them. The whole world was butterflies.
It doesn't happen anymore. We killed them. We took their food. They
weren't hurting anyone. We didn't mean to kill them. We did it by
accident. We weren't paying attention.
You can see how it would happen with e.g. insects dying off: https://news.ycombinator.com/item?id=18541536
Followed by birds that eat insects dying off: https://news.ycombinator.com/item?id=21018916
Followed by the death of everything that depends on birds and insects, which is probably a large percentage of the remaining wildlife. Similar extinction scenarios are plausible with ocean life.
I guarantee that this would result in the collapse of civilization if it were to occur.
This is one reason it's absolutely vital to halt greenhouse gas emissions. Loss of habitat and pesticides are also huge problems for insects and other wildlife, so dealing with global heating is necessary but perhaps not sufficient to save them, but we have a clear deadline for when we must reach carbon neutrality, so that seems like the top priority.