I don't quite get the downvotes, seems like a legitimate question to be.

But to answer your question, let spin the scenario I'm currently most worried about.

Let's take for a given that the antrophogenic climate change won't stop at the blue-sky +2°C that everyone is hoping so hard for (hoping, not acting). According to IPCC 2018, we're currently between +0.75 and +1.25°C, with the very real possibility of reaching +2°C by the 2040.

I know! +2°C, that not that much, isn't it! But even at +1°C, we see extreme weather. Huge swaths of India are experiencing drought like /never/ before. Glaciers, the natural water reservoirs in the European Alps, are not growing during the winter anymore. Africa, whose population is expected to continue to grow for another 50 years, is experiencing massive heat waves that threaten to make it's biggest cities inhabitable.

We thought that we had about 30 years to mitigate some of the worst damage. But now - holy shit! - the arctic permafrost is melting, about 70 years earlier than expected. And it's starting to release methane, a way more potent greenhouse gas than CO2. Sure, it rapidly decays in the atmosphere, but not before kicking us to about +4°C. This is the temperature range where some Scientists fear that frozen methane from the ocean floor will start to be released.

Hey, you say, isn't that what happened at the Permian–Triassic extinction event that killed off 96% of all marine species and 70% of terrestrial vertebrate species? Yes, exactly, I reply. But that took about 300'000 years to come to unfold. Not the 200 years we're dealing with.

So, we have a massive temperature increase at an unprecedented speed that makes huge areas of earths most populous regions inhospitable or even inhabitable. Do you think the Syrian refugee crisis was bad? Think about ~1 BILLION PEOPLE on the search for greener (literally) pastures. Do you think they will be welcome with open arms? Yeah, you bet..

Agriculture will be severely impacted. Not only by the heat, but also by the massive die-off that ensues. Because we'll be dealing with a global ecosystem collapse. Most of the animals on earth have a lifecycle that's very closely tuned to the hum of the seasons. At +4°C you can kiss all that goodbye. The only things that will survive are generalist species that have a lifecycle not tied to the seasons. (Cockroaches maybe. Certainly not butterflies. Enjoy them while they last!)

There will also be terrible conflicts and wars about the most precious resource of them all. No, not oil. We'll have oil in barrels, nobody will be lacking oil (at least at first). No, I mean water. We'll have water wars.

This will also be the time that the global economy will start to collapse. War is good for only one business, and that's weapons. Everything else will suffer. Don't expect any deliveries from your Chinese online shop of choice. Consumer markets will crash, everything will come to a standstill.

Now, this is a good moment to have a look at your counter example; the plague that killed almost one third of Europe. You're right; that didn't let civilization collapse, indeed. But you have to understand that back then, about everyone was self-sufficient. You didn't get your electricity from half a continent away. You didn't get your avocados from Peru (you didn't have any avocados, actually...). So while it might be bad that the cobbler doesn't visit anymore (because you really need new shoes), but you can endure that.

How many people nowadays are living in cities with no way whatsoever of supporting themselves for more than four days without electricity? Just make the experiment; you have no electricity anymore for the foreseeable future; how long would your dry rations last? Oh, you don't have any dry rations, everything is in the fridge? Good look then.

So, between collapsing ecosystem, the hunger riots, the wars and the waves of desperate migrants trying to survive, our global civilization will slowly be ground to pieces. We're so very interdependent nowadays that there's no workable way for it to survive the collapse of our trade networks, the wars, the walls (against migrants).

I'm very sorry about this all. I don't know what I could have done different. I wish I could look my children in the eyes and say to to them:

"There's hope. Everything will be fine."

But I can't. So I tell them the truth.

This reply got a bit out of hand, but I think your deserves a fair response. Not downvotes.