But back on the topic of physics, it’s true that there are conditions under which simplifying assumptions (let’s go with the single-object simplification of Arrhenius) are and are not safe even to get an order of magnitude estimate. Do small forcings get amplified or damped by more than 10x by feedbacks (like water vapor or cloud cover)? To what extent do other conditions (like… water vapor or cloud cover) affect the greenhouse effect from CO2?
The second one is fairly straightforward, since in the upper atmosphere (the part that radiates to space, at least in the wavelengths where the atmosphere absorbs) there’s not much competing with CO2 (since water precipitates out miles below), and so we can treat a change in CO2 as a change in energy flux and ignore some complicated stuff. The first bit is more complicated, maybe the clearest way is to look at non-CO2-caused variation in temperature: if there were too much damping or amplification we’d expect things to look different when the sun dimmed by a known amount (e.g. around 1700). We can tell from that that there’s a bit of amplification, but definitely less than 10x. So Arrhenius’ estimate should be fairly good.
I would certainly consider that positive evidence, but it’s not knock out evidence. It’s not even 90% confidence evidence, in my opinion. The data is just too noisy to draw high confidence conclusions after only a handful of years.
The IPCC must agree with you that that’s not 90% confidence evidence, because there’s a whole heck of a lot more evidence and they (well, several years ago) only gave human-caused global warming 95% certainty.
That’s just a good example of a prediction, compared to all the inference from physics and historical data.
Successful predictions, you say?
But back on the topic of physics, it’s true that there are conditions under which simplifying assumptions (let’s go with the single-object simplification of Arrhenius) are and are not safe even to get an order of magnitude estimate. Do small forcings get amplified or damped by more than 10x by feedbacks (like water vapor or cloud cover)? To what extent do other conditions (like… water vapor or cloud cover) affect the greenhouse effect from CO2?
The second one is fairly straightforward, since in the upper atmosphere (the part that radiates to space, at least in the wavelengths where the atmosphere absorbs) there’s not much competing with CO2 (since water precipitates out miles below), and so we can treat a change in CO2 as a change in energy flux and ignore some complicated stuff. The first bit is more complicated, maybe the clearest way is to look at non-CO2-caused variation in temperature: if there were too much damping or amplification we’d expect things to look different when the sun dimmed by a known amount (e.g. around 1700). We can tell from that that there’s a bit of amplification, but definitely less than 10x. So Arrhenius’ estimate should be fairly good.
I would certainly consider that positive evidence, but it’s not knock out evidence. It’s not even 90% confidence evidence, in my opinion. The data is just too noisy to draw high confidence conclusions after only a handful of years.
The IPCC must agree with you that that’s not 90% confidence evidence, because there’s a whole heck of a lot more evidence and they (well, several years ago) only gave human-caused global warming 95% certainty.
That’s just a good example of a prediction, compared to all the inference from physics and historical data.