The (surface of the) earth is warmer than if it was just heated by the sun, because it is heated by two sources: the sun and the atmosphere. [This is the inappropriately named ‘greenhouse effect’]. More atmosphere, more ‘greenhouse effect’. For the details, read the papers.Commenter, this in no way wins you a £5 voucher. A ‘Fermi explanation’ has to be a complete chain of reasoning from cause (or evidence) to effect. Approximations are OK, so are gross assumptions, so long as they are reasonable assumptions, but every link of the logical chain has to be visible. Your comment is wholly useless in this respect. It doesn’t explain the relation between carbon emissions and ‘atmosphere’, nor the relation between ‘atmosphere’ and temperature, nor the relation between temperature and ‘damage’ or ‘harm to planet’. So, no prize, sorry.
On ‘read the article’, about a year ago I got tired of reading stuff about ‘scientific consensus’ and tried to work the whole thing out for myself. It was surprisingly hard. Wikipedia articles like this are a useful overview, but they remind me of those science books I read avidly at the age of 8, how telephones work, how air brakes work, how jet engines work. A useful ‘pictorial overview’, but without depth of explanation. This article is much better, but fails for two crucial reasons. First, it is mathematical. Although the mathematics is not very difficult, there are many people to whom this kind of reasoning is impenetrable. A verbal, or pictorial explanation (or a combination of those modes of explanation) is needed to explain the underlying reasoning, without the maths. The second fault is far worse, because it fails to connect the variable representing the amount of atmosphere, with the industrial process. It neatly explains in a quantitative way how increases in epsilon correspond to changes in equilibrium temperature. But it doesn’t explain how emissions in carbon dioxide are related to epsilon*. Which is what we wanted to know. How much is my stash of incandescent bulbs likely to increase the equilibrium temperature of the earth? Don’t know, and I am keeping the stash for now.
*To be fair, the article does state this implicitly, in the bit where it says “The radiative forcing for doubling carbon dioxide is 3.71 W m−2”. But it doesn’t explain where that figure comes from, nor does the article http://en.wikipedia.org/wiki/Radiative_forcing it links to. And it only gives figures for carbon dioxide emissions. As I mentioned in the previous post, carbon dioxide is not the only greenhouse gas.
6 comments:
You're cheating, by moving the goalposts. You started by saying:
> I am a global warming sceptic in the sense that I remain unconvinced that it exists
by which I understood you to mean that (a) you don't believe the earth is warming (implausible, I think) (b) you don't believe the current warming is caused by people. I assumed (b). Now you're insisting on proving harm, or something else.
So before you go any further, can you give a precise statement of exactly what it is that you require proved?
>>by which I understood you to mean that (a) you don't believe the earth is warming (b) you don't believe the current warming is caused by people. I assumed (b). Now you're insisting on proving harm, or something else
<<
Apologies, I accept I was not being clear. (b) is obviously and unquestionably true.
The proposition I am sceptical about is "The notion that increasing atmospheric concentrations of greenhouse gases, notably carbon dioxide, will have disastrous consequences for mankind and for the planet".
We need a 'Fermi explanation' for that one.
Ah, I wish you'd said that at the start. I'd have pointed you to: http://www.realclimate.org/index.php/archives/2004/12/just-what-is-this-consensus-anyway/
I don't think the "disastrous" bit is part of the scientific consensus (depending, of course, on the undefined word "disastrous". Would halving of GDP be disastrous, or would it need deaths of half the population?). I know you included "disastrous" right at the start, but I just assumed that was strawman stuff (where you started, http://www.firstthings.com/article/2011/05/the-truth-about-greenhouse-gases, is junk, of course).
If you're entirely happy with all the IPCC WG I report (in which case, I fail to understand why you're quibbling about logarithmic, or WV) the we have no real difference of opinion on the matter.
Where I started was Bill Vallicella's post, which linked to the 'junk'. I didn't read much of the article, the bits I saw were rehashes of other things I had seen before.
On the 'logarithm' thing, this is more a matter of exegesis rather than science itself. My understanding of the science is
(a) The amount of 'atmosphere' determines an equilibrium temperature of the globe. We are never at the equilibrium temperature because there is a considerable fluctuation around it. Nonetheless there is an equilibrium, and all things being equal the long term average would approach it. (Talking to friends and colleagues, some of them think that the mere presence of carbon dioxide is enough to cause a constant increase in temperature, even without any change in composition).
(b) ‘Global warming’ in the narrow sense is simply the direct cause of *increasing* amounts of atmosphere/greenhouse gases.
(c) The point about the logarithmic effect is that (based on talking to people) even those who do understand that warming corresponds to increase in greenhouse gases think that the relationship is linear, i.e. the more greenhouse gas we pump into the atmosphere, so in proportion the temperature increases. My understanding is that this is wrong. I.e. if doubling the greenhouse gas produces an increase in equilibrium temperature of x, then to cause an increase of 2x you have to quadruple the greenhouse gas concentration. And to produce 3x, multiply by 8, and so on. If we assume constant rate of emissions (not valid, I agree), that gives pretty long time scales.
I had a look at just-what-is-this-consensus-anyway and I note the last point – namely that there is no consensus on “This will be a problem and we ought to do something about it”. That’s it then. No one ever said anything I need be sceptical about!
I had a brief look at the report which is linked to. I have a big problem with “Statistical assessments confirm that natural variability (the combination of internal and naturally forced) is unlikely to explain the warming in the latter half of the 20th century.”
You write, "First, it is mathematical. Although the mathematics is not very difficult, there are many people to whom this kind of reasoning is impenetrable. A verbal, or pictorial explanation (or a combination of those modes of explanation) is needed to explain the underlying reasoning, without the maths."
This is a rather bizarre statement. There are lots of important things that can't truly be explained (proved, actually) without the maths. In most cases, one can produce a plausible description of the situation, but to know whether the plausible description is accurate or not, you have to do detailed analysis.
I wonder if your subtitle "Medieval Logic" is more accurate than I took it for -- the difference between medieval logic and science is mathematics.
Welcome achinhibitor.
"There are lots of important things that can't truly be explained (proved, actually) without the maths. In most cases, one can produce a plausible description of the situation, but to know whether the plausible description is accurate or not, you have to do detailed analysis."
There are quite a lot of things in here, so difficult to comment. You are talking about (1) proof (2) explanation (3) description (4) accuracy. I would definitely agree with you on accuracy. The logic of ordinary language (e.g. medieval logic) is focused on generality. 'The earth is spherical' is a general statement which is not altogether accurate. On 'proof', I had an argument two weeks ago with a mathematical economist. He went on in the usual way, proving that A implies B, taking about 10 pages, and presenting this as a proof. Which it was. But when with some difficulty I followed the proof through, of course A did imply B. But the problem was with A. A vague and unverifiable statement had been smuggled inside A. One of the terms was practically meaningless. But the mathematics obscured that.
Also, you are commenting on a post made in 2011. Following that, I went offline with another commenter here (a skilled mathematician) and we worked through the Wikipedia mathematical explanation of forcing. An important bit had been completely left out. Again, the mathematics obscured this.
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