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Why the laws of physics make anthropogenic climate change undeniable

There have been quite a few articles on the climate on recently. I've not done a statistical analysis to see whether there has been a significant rise in the frequency with which that topic comes up here, but let's just say it seems like there has been. I figured it was worth creating a discussion of one aspect of the issue that hasn't been talked about much and that hasn't had many pertinent resources shared. There are 2 reasons a given phenomenon should be real in science, and we usually have both of them: the evidence can say it's true, and the laws of physics can say it's true. We haven't talked much about the latter, and that's what I will do here. It goes without saying it will involve a lot of equations I can't type here, but that's OK as I'll be linking to external material. I know maths scares or overwhelms a lot of people, but luckily these PDFs intersperse fairly verbal explanations with equations as they go along, so I think it should be OK.

I don't think those who doubt the reality of our CO2's effect on the climate realise just how many laws of physics they have to snub as part of that denial. When I was an undergraduate almost all our syllabus material was theory rather than evidence, not because evidence doesn't support the material (it does in spades), but because (a) it takes much longer to derive the theory than to notice what it would imply about data and say, “And we did the experiment and yes, it does work that way”, and (b) physicists learn as much from proving theorems in their theory (e.g. “Even though we've never seen A, it has to be true because of B, which we're sure is right because it correctly predicts C” or “D and E don't gel, so one's got to go”) as they do from the empirical data. Of course the ultimate say goes to data, and if a purported law is eventually shown up it's out. But it was made crystal clear to us in our climatology lectures just how directly uncontroversial physical laws inexorably lead to all the stuff you've heard – “CO2 warms Earth”, “The sea will rise”, “Thermohaline circulation will happen, at least in part and for quite a while”, “The polar ice caps won't easily and quickly recover even if Earth cools again”, “Our effects on the oceans will be with us for a very long time”. And when I say it was made clear, I don't mean they told us so, I mean they showed it.

I am a scientist, and when I claim something, I must immediately accept the following challenge: “Put up or shut up”. And I'm here to put up, with lecture notes. I want to share these links with you all so you can have fun reading them, because I know how much most people here enjoy learning something new. I know a problem we rationalists face is how to better disseminate the scientific facts to the public, and I don't really can't say how to do that, but here I'm doing what little I can to give people here some food for thought.

The first part is third year notes on a course of 10 lectures. Like a medical degree's review of human biology, its first half is how things work when things are going well, which the second half looks at how it can mess up; it therefore seemed worth including the titles to help you dive in where you want:
Thermodynamics of a dry atmosphere
Moist atmospheric thermodynamics
Atmosphere-Ocean General Circulation
Radiation in the Atmosphere
Radiative transfer and radiative forcing
Forcing, feedbacks and the climate response
Changes in other climate variables Part 1
Changes in other climate variables Part 2
Abrupt climate change

The rest is fourth year material. It may repeat the earlier stuff somewhat. The main meat of it is this 6-part lecture series. For some reason these PDFs make it very hard to leave the page, at least in my browser (Firefox), so I recommend opening one of these in its own tab first to see how easily you can, for example, change a number in the URL to go to the next one, or go to any other page at all, or search Google from a toolbar. It's focused mainly on the oceans, as you can see from the titles:
Air-sea interaction and circulation
Wind-driven circulation
Western boundary currents
Vertical structure of wind-driven gyres
Meridional overturning circulation
Oceans and climate variability

There's even more information on radiation (and what influences it, including CO2) in this “lecture 1” (it's standalone).

Finally, I know I said my focus was on theory, but the next step is how you relate that to evidence, right down to the error bars on conclusions. How do we measure all this? How do we know how accurately we can describe it? For all that, see here.


MORE BY Jos Gibbons



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