Are you actually insinuating that the collapse of the AMOC is as unlikely as a zombie outbreak?

No, it's just as likely. It was to illustrate a point that there's many "possible catastrophes" waiting for us and governments should be prepared for all of them. But writing sensationalist articles predicting the end of the world is not how it's done. They want to increase anxiety, so people become scared and start making dumb decisions, like mob mentality. The downvotes on my post prove my point. People are confused and scared and are going to do whatever the closest perceived authority tells them.

Because the report actually states that the IPCC category of “medium confidence” is applied to the prediction the AMOC won’t collapse in this century. And the open letter is published because the scientists believe that the IPCC has underestimated the risks.

Yes, exactly. Regular doomsday predictions aren't bringing in the money they used to, gotta turn it up to 11. My favourite part is how they say that it can collapse this century, but it won't be apparent until the next century (when conveniently all the undersigned scientists will be dead).

Funny you say that since China is the one country in the world doing the most to keep warming

Without writing a single open letter?! I don't believe it.

Their work on developing renewable is why we even have a chance of succeeding

You're making it sound like the only motivation a country can have for switching to renewables+nuclear is "to save the environment" (or some other slogan), but consider this: renewables decrease the amount of CO and CO2 in the air, China has problems with air quality; renewables and nuclear reduce dependence on oil trade, increasing self-suffiency and protecting from sudden price increases of oil, etc. China is also producing the most coal plants in the world too. You shouldn't assume just because someone does what you'd do that they're motivated by the same things.

How is first person or third person relevant?

"We" or "I" is a personal pronoun that refers to a group of people or person. Saying "Science confirms..." is giving agency to something that exists only in the abstract ans therefore cannot confirm or deny. They didn't write "Scientists from this and that university confirmed..."

Are you going to tell me that all of the communists who sacrificed their lives to create the PRC and USSR did so out of selfishness?

Why else? They certainly didn't do it so that someone would praise them online for it a hundred years later. Also, most people don't do things thinking they will certainly die, they do them regardless of the possibility of death. And yes, they did it to make a better life for themselves, their families, their friends, community and children.

For example, I pick up garbage on the street where I live out of purely selfish reasons, not for the environment, not because I hate littering, not because I want to make the world a better place, but because I love there and I don't want the place I live to be littered with garbage, it looks bad.

If everyone started looking out for their actual interests and started acting selfishly, we'd have full communism in a week. We don't have communism precisely because people are convinced to act against their own interest by ideology.