I spent most of this weekend calculating solar elevations at different latitudes and different times of the day, which involved a lot of messing about with sines, cosines and tangents (and a lot of simplifications and sensible assumptions, which you have to test back and forth until you get plausible results).
The reason for this was to look into a theory expounded by climate contrarian Joseph Postma. His theory is that Alarmists wilfully understate incoming solar energy by assuming that the earth is flat and sunlight arrives smoothly over each 24-hour period at an average rate, instead of it all arriving in the day time. So I needed to have a spreadsheet that worked out incoming sunlight and outgoing radiation for every minute throughout a 24-hour period, for which I need to know solar elevation. It turns out that while the Alarmist approach is deeply flawed and misleading, the answer you get from averaging is not wildly different than if you do it properly.
Postma should know that, but he has lots of other very useful insights. So much so that Skeptical Science has a whole page dedicated to slagging him off.
After I finally got the spreadsheet to work, I did a proper 'daily radiation budget' for somewhere at latitude 45N close to sea level (which happens to be Bordeaux, France). 45N or 45S is a good place to start because at that altitude you know that solar insolation is precisely the average for the whole planet. After more tweaks, I got daily high, low and average temperatures to match up perfectly for the month of September, which is the month of the autumn solstice. Arguably, this overstates temperatures because it's still warm from the summer; but the model also overstates temperatures because I ignored the +/- 23 degree wobble of the earth, and the two effects seem to cancel each other out.
I did one tab for ground level and the boundary layer (the lowest 500m of atmosphere, where the temperature is similar to ground level) and the next tab for ground level plus the column of troposphere above it (10 km up), both as adjusted for the gravito-thermal effect. They reconcile nicely with each other.
The main lesson here is that you have to make endless assumptions for albedo and emissivity and so on (starting with traditional assumptions and tweaking) and you can only get the starting temperature by trial and error - if you set it too high, you get too much outgoing radiation, which indicates cooling as incoming solar radiation is fixed (and vice versa). If you change albedo or emissivity by one percent, you get an additional degree of warming or cooling.
You can firm up on these tweaks and assumptions, I suppose, but in doing so, you would have to make more tweaks and assumptions to resolve the uncertainty; and more tweaks and assumptions to resolve those... until you end up with a house of cards ready to collapse at the slightest peturbation.
Sunday, 31 January 2021
Fun with climate models
My latest blogpost: Fun with climate modelsTweet this! Posted by Mark Wadsworth at 18:43
Labels: global warming, Science
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14 comments:
Interesting. It is pretty well impossible to believe that climate model folk don't work backwards from the kind of results they want.
What you're saying, then, is that, in effect, the models on which the whole of climate "science" is built can always be tweaked to give the desired result. In other words, it's all policy-based evidence, as you, me and AKH suspected.
AKH, B.
You've reminded me why I actually bothered. I've added a paragraph explaining why: I was investigating a contrarian theory that - while appealing - turns out to be not particularly true.
Apart from that, the game was just to do something that gave realistic results, so yes, I started with basic principles but equally, I was working backwards from a known (i.e. desired) result.
B. Policy based evidence making is I believe the phrase. Happens all the time and everywhere.
MW. So, I understand that all this 'science' is extremely sensitive to small changes in assumptions?
L, "this 'science' is extremely sensitive to small changes in assumptions?"
Yes, all the models do is confirm that whatever assumptions you made are correct.
If you assume that there is a direct correlation between average temp and CO2 levels and run it from 1980 onwards, you get a good match proving that, er, temperature is directly correlated to CO2 levels.
Hmm. So that's correlation, not necessarily causation.
L, indeedy!
If you spend a year delving into this, which I have done, they started from one end - theory = CO2 = warming - and then from the other end - measured temperatures, to the extent they are accurate - and then considered this as proof of causation in one direction
It could just as well be causation in the other direction - warming = CO2, or mere coincidence - the real cause is more likely ozone depletion.
Ozone depletion. Read that in your other post. It makes more sense to me. And we've fixed that.
What 'we' need is a large island somewhere - temperate to warmish (sic) - where 'we' can all move to and conduct our lives without all this crap.
L, we've not fixed ozone. Some naughty countries are still making CFCs, and there is a lot of it left which is drifting slowly upwards into the stratosphere, where it does the damage. It will be decades before ozone has returned to pre-1970s levels.
MW. OK then. Partially fixed the CFC/ozone issue. So who's still making and releasing CFC's? Let me guess. China? The USA?
Ah....
https://www.theguardian.com/world/2019/may/23/china-factories-releasing-thousands-of-tonnes-of-illegal-cfc-gases-study-finds
Admittedly the Gruniad, but...
L, the measurements show that it's mainly China. The Americans have developed far less damaging alternatives.
From the Gruniad article:
Two decades ago, CFCs – more potent by far as greenhouse gases than carbon dioxide or methane – accounted for about 10% of human-induced global warming.
Someone has been there ahead of you?
L, CFC's have two quite different effects, the G only talks about one of them (the minor one).
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