this post was submitted on 31 Jul 2023
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IPCC projections barely cover anything past 2100. I'm an environmental scientist and I'm telling you, the earth's equilibrium systems will only tend towards the current status quo within a narrow range of parameters. When global warming rises over a few degrees, the systems that currently keep the earth cool will fail. We don't know what the new equilibrium point looks like after that. But we do know human beings did not evolve to live on that environment, and there is zero guarantee that we aren't going the way of the wooly mammoth.
What you write suggests to me that temperatures would, in a worst case scenario, rise beyond approximately +4C after 2100. Often, when I read comments, they seem to imply runaway climate change. Last I checked science was saying that this seems very unlikely to be possible at all, and that a hothouse earth would possibly reach a stable state at approximately +4C.
I also figure that most people to not know that additional warning would require more, and not less CO2. As far as I know, research has shown that humanity would likely not be capable of reaching such a level of emissions.
So, what we are left with is the +4C scenario. Its consequences are uncertain enough, that’s fair. However, when you say that this is an environment humans did not evolve to live in, while technically true, it just makes it sound a lot more dramatic than it probably is likely to be.
To get back to the initial claim about the end of human civilization, this clearly requires unsurvivable conditions globally, including in regions least effected by climate change. While this may sound cynical, the worst effects that are likely to affect Africa, the Sahara, or the Middle East, certainly to not mean the end of human civilization. Implying so is in my opinion dubious. If we look at that Wikipedia article that has been shared, there seems to be a lot of handwaving about a combination of effect supposedly somehow combining to lead to humanity’s extinction mostly by triggering migration and wars. A dubious proposition.
Without trying to go into conspiracy territory, it often seems to me that scientists are hesitant to clearly communicate basic facts around climate change that might be used to oppose needed climate action.
And for the record, I agree that action is needed. However, I disagree with spreading apocalyptic scenarios that seem very unlikely to even be possible, much less a likely outcome. Studies have suggested that climate fears affect a large number of young people, it’s in my opinion a mental health concern. People online love to fuel it, there’s nothing more popular than climate change hyperbole.
Weren't there periods in the past where temperatures were "a few degrees" higher and still had conditions that could sustain human life?
Here is a very good graph demonstrating the first part of the problem:
https://xkcd.com/1732/
The globe is warming faster than any animal can adapt. And it's going to keep warming, even on net zero emissions, because the carbon dioxide is already in the atmosphere.
The second part of the problem is that previous periods of warming did not involve the release of underground carbon reserves. That carbon has been there since the age of the dinosaurs. That carbon is going to CONTINUALLY warm the earth, it's not going to just stop warming up like a volcanic eruption. Not until it's recaptured and buried.
Also, the carbon dioxide is turning into carbonic acid in the oceans, and we haven't felt most of the effects of that because the calcium carbonate buffer has been protecting us. When the buffer runs out, we're going to see some very big changes very quickly.
According to graphs I have seen, this won't be the fastest warming period ever, even by worst predictions. Example: https://scitechdaily.com/images/Past-and-Future-Global-Temperature-Trends-scaled.jpg
The second problem I have with your post is that there were far higher CO2 levels in history which didn't correlate with temperature rises.
Also, a lot of this global extincion theories are just theories that are based on predictions that are dependant on inputs and not all inputs (not even close) are considered in those calculations. Even IPCC itself thinks not including clouds feedback (and it's dominant termostatis control of temperature) could be a potential problem in their predictions.
All in all - human extinction theory is not something there is a consensus for and it certainly is a part of alarmism.
However, scientists have conclusively demonstrated that in the 19th through 21st centuries, CO2 emissions directly predict rises in temperature.