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Comment by delecti | Hacker News Reader

It may require a complicated computer model to pin down exactly what the effects will be, but it doesn't take any of that to accept the basic premises that lead to accepting climate change. We know (and have known for over 100 years) that CO2 in the atmosphere slows the escape of heat energy, which means the equilibrium temperature will go up. The specifics of 1 degree or 1.5 or 1.6 are more complicated, but it's really as simple as that. When I was in grade school, we learned that there were 300 PPM of CO2 in the atmosphere, and now they're learning that there are 400 PPM of CO2.

It may take some math to figure out how much warmer you'll get, but it's simple enough to realize that if you go outside on a comfortable sunny day, and then put on a blanket, you'll get warmer.

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It isn't actually that simple, though. Adding CO2 to the atmosphere in isolation, with no reaction from the environment will indeed cause warming. But we don't live in a static model. The environment reacts to things in complex ways. It's entirely possible that adding CO2 to the environment could have caused cooling, in equilibrium (by, e.g. increasing tree density in response to the increased fuel, leading to an ultimately cooler climate). It doesn't happen to work out that way, unfortunately, but it was a possibility.

Without knowing if there were some mechanism that could balance the effect of added CO2, it would indeed be possible for such a thing to exist. Without checking, you couldn't assume it didn't exist, but coming from a place of ignorance, it's not reasonable to assume such a thing does exist. So without making unfounded assumptions, upon learning that CO2 insulates, the reasonable conclusion is that the measurable increase in CO2 (~300 to ~400 PPM) will lead to warming.

There is a vast gulf between "we should assume it would be likely to cause warming, all else equal", which is more or less reasonable, and "We have proven that it would definitely cause warming".

There's no reason to assume the complex models and naive assumption don't match though, which is the point I'm trying to argue. If the first step is "we should assume it would be likely to cause warming, all else equal", then there's no reason to jump to assuming the complex models disprove that basic assumption. They might, they do in plenty of circumstances, but it's reasonable for the working assumption to start from assuming they match. The naive assumption should convince most ignorant people (which is virtually everyone, almost nobody is doing PhD level climate research, and not many more really understand that research) to listen to the PhD scientists shouting the same thing. It's not reasonable to deny the conclusion of climate change scientists with complicated models just because you don't understand them, when the simple science agrees.

There are very good reasons to do exactly that. I don't know how often you work with complex models like this - but I do all the time. They are very often wrong for very subtle reasons. It's extremely difficult to satisfactorily prove something in a descriptive analysis, especially of a complex, dynamic system.

By default, you should basically never trust any descriptive analysis of a system like climate or the economy. Climate change specifically has received so much scrutiny by now that it's probably trustworthy. But in general you should have a very low prior on this entire category of research.

You seem to be deliberately avoiding my point. The fact that some complicated models are wrong is irrelevant. The fact that you've worked with lots of complicated wrong models is irrelevant. The rational default assumption for a lay person, when the experts say that their complicated model agrees with the simplified model which can be explained to the lay person, is to tend to accept what those experts say. It makes no sense to go from "I understand the grade school science behind climate change" to "but those experts use complicated science, so they're probably wrong".

Yes, the rational default for a lay person is to accept expert consensus. But the question at hand is what weight they should give that consensus. And that weighting should change, depending on the nature of the system being understood. We're talking about credences, not point estimates of beliefs.

Every time I've seen someone suggest that plants could have taken up the load it seems trivial to demonstrate this is not the case.

For plants to take up the load, they would need to absorb and retain 30,000,000,000 tons of additional plant matter annually. A pine tree can absorb ~1 ton/year. If you put 100 per acre, and assume the trees are 100% sequestered, you'd need 30,000,000 acres (50,000 sq. miles) of additional pine forest, where none of the material was allowed to decay back into CO2 just to break even.

Plants don't generally sequester much of the carbon they capture in their lifetimes naturally. Mostly it's the root matter of the plant that stays sequestered. So, if you wanted the world to take this up without human intervention, you'd have to figure out how to get 30,000,000,000 tons of root matter generated each year.

I agree, but that's beside the point. The point is that the earth is a complex, dynamic suite of feedback loops, where changing one knob does not necessarily lead to the simplistic outcome that it might, if all else were held constant.

Please take this question in good faith, as I am not a denier, but how do we rule out unknown earth-scale homeostasis mechanisms without a full understanding of the whole system?

If you have any links or thoughts I'd appreciate it

I think most folks aren't super worried about a Venus-like runaway scenario where the planet starts boiling lead.

Instead the concern is that while the planet will reach homeostasis over the long term, in the short term it will cause mass extinctions, destroy coastal communities, disrupt food production, destabilize governments, etc.

It's like saying, "Won't a city rebuild after a major disaster?" Yes, of course. New Orleans wasn't completely eradicated by Katrina. But it was also awful. If we had it within our power to avoid a disaster, we should try to avoid it.

It's known that there were "greenhouse periods" in the distant past where substantially all the glaciers melted, so whatever homeostasis mechanisms might exist can't be strong enough to prevent that scenario.

We can look at the geological evidence from past periods when atmospheric CO2 was higher than 280 ppm. And of course that has been done in great detail.

The evidence confirms the theory.

The problematic aspects of climate change aren't its first-order effects. The worst case scenarios involve warming by a couple of degrees Celsius - much smaller than existing variations from day to day or city to city. The only reason we're concerned is that we expect, based on climate modeling, that a worldwide shift of even this relatively small magnitude will have large second order effects.

But you're getting into "why is warming bad?", when the issue is people doubting that warming might be an outcome at all.

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