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gwern comments on Separating the roles of theory and direct empirical evidence in belief formation: the examples of minimum wage and anthropogenic global warming - Less Wrong
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Comments (65)
Yes, but some googling suggests that average snowfall in England hasn't changed very much over the 2000s, which doesn't seem consistent with the linked article.
"Over the 2000s" is certainly too short a period to reach significant conclusions. However the longer term trends are pretty clear. See this Met Office Report from 2006.
Figure 8 shows a big drop in the length of cold spells since the 1960s. Figure 13 shows the drop in annual days of snow cover. The trend looks consistent across the country.
I think the first question here is whether we have reached agreement on the forecasts being wrong, not what excuses should be made or conclusions drawn from said wrongness.
Yes, I'm sure they were, and that those were the basis for the mistaken prediction. Your point?
I think we have agreement that:
A) The newspaper headline "Snowfalls are now just a thing of the past" was incorrect
B) The Climatic Research Unit never actually made such a prediction
C) The only quoted statement with a timeline was for a period of 20 years, and spoke of heavy snow becoming rarer (rather than vanishing)
D) This was an extrapolation of a longer term trend, which continued into the early 2000s (using Met Office data published in 2006, of course after the Independent story)
E) It is impossible to use short periods (~10 years since 2006) to decide whether such a climatic trend has stopped or reversed.
I can't see how that counts as a failed prediction by the CRU (rather than the Independent newspaper). If the CRU had said "there will be less snow in every subsequent year from now, for the next 20 years, in a declining monotonic trend" then that would indeed be a failed prediction. However, the CRU did not make such a prediction... no serious climate researcher would.
From the article:
Does heavy snow cause chaos in England now?
Is snow a 'very rare and exciting event' in England now?
If we asked them, would they not know first-hand what snow is, anymore than they know first-hand what wolves are?
You can't?
What's the date?
By your reaction, and the selective down votes, I have apparently fallen asleep, it is the 2020s already, and a 20-year prediction is already falsified.
But in answer to your questions:
A) Heavy snow does indeed already cause chaos in England when it happens (just google the last few years)
B) My kids do indeed find snow a rare and exciting event (in fact there were zero days of snow here last winter, and only a few days the winter before)
C) While my kids do have a bit of firsthand knowledge of snow, it is vastly less than my own experience at their age, which in turn was much less than my parents' experience.
If you are a resident of England yourself, and have other experiences, then please let me know...
Well, all the quotes I gave were drawn from http://www.independent.co.uk/environment/snowfalls-are-now-just-a-thing-of-the-past-724017.html which was 14 years ago. That sounds like it'd cover 'within a few years'. And as for the exact 20 year forecast of 2010, well, that's just 6 years away. Not a lot of time to catch up.
Yes, looks like the usual chaos you could find in the '80s and '90s to which the predicted 'chaos' was being compared as being greater.
And has your region changed much? And is your anecdote very trustworthy compared to the nation-wide changes in snowfall since 2000 (not much) when these predictions were made?
Sigh... The only dated prediction in the entire article related to 20 years, not 14 years, and the claim for 20 years was that snow would "probably" cause chaos then. Which you've just agreed is very likely to be true (based on some recent winters where some unexpected snow did cause chaos), but perhaps not that surprising (the quote did not in fact claim there would be more chaos than in the 1980s and 1990s).
All other claims had no specific dates, except to suggest generational changes (alluding to a coming generation of kids who would not have experienced snow themselves).
Regarding the evidence, I already gave you Met Office statistics, and explained why you can't get reliable trend info on a shorter timescale. You then asked anecdotal questions (is snow "rare and exciting", what would kids say if you asked them?) and I gave you anecdotal answers. But apparently that's not good enough either! Is there any set of evidence that would satisfy you?
Still if you really want the statistics again, then the very latest published Met Office set runs up to 2009 if you really want to check, and the downward trend lines still continue all the way to the end of that data. See for instance this summary figures 2.32 and 2.35.
So if you want to claim that the trend in snow has recently stopped/reversed, then you are looking at a very short period (some cold winters in 2010-14). And over periods that short, it's entirely possible we'll have another shift and be back onto the historic trend for the next five year period. So "catch up in six years" doesn't sound so implausible after all.
I'm sorry, I didn't realize 'within a few years' was so vague in English that it could easily embrace decades and I'm being tendentious in thinking that after 14 years we can safely call that prediction failed.
So first, that's 'air frost' ("usually defined as the air temperature being below freezing point of water at a height of at least one metre above the ground"), which is not what was in question. Second, looking at 2.32, the decline 2000-2007 (when the graph ends, so fully half the period in question when warming seems to have stopped) is far from impressive. Third, what's with it being 'filtered'? some sort of linear smoothing borrowing from the steeper-looking decline 1984-2000?
No, I'm fine with your chosen smoothed graphs indicating only a shallow decline at best 2000-2007. No need to look just at 2010-2014, although certainly more recent data would probably help here.
That sounds like wishful thinking. In those graphs, is there any 5-year period which if repeated would abruptly vindicate the confident predictions from 2000 that snow would soon be a thing of the past in England?
P.S. On the more technical points, the 2009 reports do not appear to plot the number of days of snow cover or cold spells (unlike the 2006 report) so I simply referred to the closest proxies which are plotted.
The "filtering" is indeed a form of local smoothing transform (other parts of the report refer to decadal smoothing) and this would explains why the graphs stop in 2007, rather than 2009: you really need a few years either side of the plotted year to do the smoothing. I can't see any evidence that the decline in the 80s was somehow factored into the plot in the 2000s.
Got it - so the semantics of "a few years" is what you are basing the "failed prediction" claim on. Fair enough.
I have to say though that I read the "few years" part as an imprecise period relating to an imprecise qualitative prediction (that snow would become "rare and exciting"). Which as far as my family is concerned has been true. Again in an imprecise and qualitative way. Also, climate scientists do tend to think over a longer term, so a "few years" to a climate scientist could easily mean a few decades.
And you're right, no further 5 year period would make snow "a thing of the past" but we already agreed that was the Independent's headline, and not CRU's actual prediction. Rare snow in the 2020s is different from no snow in the 2020s.