First, thanks for asking.

Next, let me qualify "global civilization is about to tank..." by adding
"...unless we have some sort of Spiritual transformation of some kind."
I hope that will happen, but this isn't the forum to get into what are
essentially religious beliefs, eh?

Further, I believe that we actually have all the technology we need to
enact a wonderful quasi-utopia. I'm a Bucky Fuller fanboy, and he
basically laid out the math (he was an engineer) to show that, if we
applied our technology efficiently to our problems, we could create a kind
of secular utopia "without disadvantaging anyone". That's even before
you get into things like applied ecology ("Permaculture" et. al.), or
fusion power, etc. We even have the psychological science now to
reprogram our minds. If we chose "be better people" as a goal there is
no time in history more amenable.

Now then, to answer your question,

> Why do you think that?

The simple answer is that I read some books about ecology as a child and
realized that our civilization is predicated on the destruction of life.
We literally destroy living things, everywhere, all the time.

(As an aside, I've never understood how people compartmentalize the world
as "the environment" and folks who care about other [non-human] lives as
"environmentalists", as if the environment is some object or fetish.
Every breath is a bond.)

The only reason we haven't tanked already is due to the truly massive
inertia and resilience of the living world. We are strip-mining the
oceans of biomass and returning plastic. Our agriculture "mines" the
soil and causes erosion.[0] Together with our meat animals we outweigh
all other terrestrial animals by an order of magnitude.[1] I could go
on, at great length.

Since my childhood, I've seen that the ecological destruction has only
gotten worse. And, while some people have started to change their
attitudes towards Nature, the bulk of humanity seems to be just as
self-centered and destructive as ever. And now they are distracted by
their phones.

Also, we are absurdly not-quite-smart. E.g. refrigerators that open like
cabinets instead of drawers. Every time you open a fridge, the cold air
spills out and is replaced by some warm air, and the fridge then has to
cool that air off when you close the door. I can't begin to imagine the
energy we could conserve just by changing that one stupid detail.

Everything is like that. I could go on, at great length.

You mention nukes...

> The most recent officially announced setting— 2 minutes to midnight —was
made in January 2018, which was left unchanged in 2019 due to the twin
threats of nuclear weapons and climate change, and the problem of those
threats being "exacerbated this past year by the increased use of
information warfare to undermine democracy around the world, amplifying
risk from these and other threats and putting the future of civilization
in extraordinary danger.”

https://en.wikipedia.org/wiki/Doomsday_Clock

So, um, yeah...

We have massive, serious problems and I don't see enough people and
nations making the comprehensive changes that would be necessary to avert
them.

[0] "Soil and Civilization"
https://archive.org/details/SoilCivilization/page/n3
https://www.goodreads.com/book/show/14060428-soil-and-civili...

[1] https://xkcd.com/1338/

> Earth's LAND MAMMALS By Weight [[A graph in which
one square equals 1,000,000 tons. Dark grey squares represent humans,
light gray represent our pets and livestock, and green squares represent
wild animals. The squares are arranged in a roughly round shape, with
clusters for each type of animal. Animals represented: Humans, cattle,
pigs, goats (39 squares), sheep, horses (29 squares), elephants (1
square). There are other small, unlabeled clusters also. It is clear that
humans and our pets & livestock outweigh wild animals by at least a
factor of 10. ]] {{Title text: Bacteria still outweigh us thousands to
one--and that's not even counting the several pounds of them in your
body.}}