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passive_fist comments on Open thread, Sep. 28 - Oct. 4, 2015 - Less Wrong Discussion
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I'm really hesitant about posting about controversial topics like climate change because of the heavy mind-killing effect they have. But I was recently involved in a debate about climate change, and one of the opponents in the debate pointed to evidence supposedly supporting the 'global warming hiatus' in the past 15 years and that 90's climate models did not predict the hiatus. On the other hand, work by NASA/NOAA suggests that the supposed hiatus is actually illusory and an artifact of uncorrected ocean temperature data. Other sources suggest that the time period in question is too short to say with high confidence whether a hiatus has occurred or not.
Both sides of this debate agreed that climate change was happening; the disagreement was just over the existence of a recent hiatus in land-ocean surface temperature warming and the predictive power of climate models. I am not experienced enough in climate science to determine what the truth is here. Does anyone have any more information?
There are a lot of decade-scale cycles that pump heat energy around the earth system, making it pile up more rapidly in the atmosphere than the deep hydrosphere or vice versa, and various other similar things . Patterns at timescales shorter than a decade or so are almost meaningless as a result.
That certainly wasn't what global-warming people were saying at the end of 1990s.
Well the question is less about heat energy and more about land-ocean surface temperatures. In the debate, both sides agreed that the climate heat content was increasing and that this was due to human activity. The disagreement was about whether surface temperature models should be taken seriously or not.
"Suitability of climate models" is a... complex subject. I don't think there is a short and easy answer other than that most models overstate the certainty of their conclusions.
Whether the hiatus ("pause") exists is a much easier question. Just take a look at temperature plots for the last 50 years or so and check what your eyes tell you :-)
This is the same procedure that leads a lot of people to lose a lot of money trying to pick stocks, and a lot of other people to believe in the efficacy of prayer. Human eyes attached to human brains are very good at seeing patterns that aren't really there.
I am not a climate scientist and haven't looked at the data in detail. But, for what it's worth, when I eyeball the plots what I see is a highly noisy time series whose last 10 years or so do indeed look cooler than trend but not so much so that I'd want to rule out random variation as a sufficient explanation. And at least some people who have looked at the data in detail have arrived at the same conclusion; see e.g. passive_fist's second and third links.
I don't know whether those people are right, but what they say seems to me obviously credible enough that saying "just eyeball the data, it's obvious" is really bad advice.
[EDITED to add:] Maybe what's actually going here is different interpretations of "the hiatus exists". It seems fairly uncontroversial that (e.g.) the slope of the least-squares straight line fit to mean surface temperature from 1998 to 2013 is somewhat smaller than that of a corresponding fit from 1983 to 1998. (Though IIUC this is in fact what the NOAA guys are calling into question.) On the other hand, it's obvious from, er, eyeballing the data that whatever medium-to-long-term trends there may be are overlaid with a lot of short-term variation, and the question is: does that fact about slopes of 15-year fits actually give us reason to think that whatever processes are responsible for the longer-term increase in measured temperatures have stopped or slowed or otherwise changed? The answer to that could well be negative, and my own impression on eyeballing the data is that it probably is negative, and that's what I mean by saying it's doubtful whether there has actually been a hiatus.
I'm not afraid of a long and hard answer, if you have one.
Looking at the official data released by NASA, there is no warming hiatus.
The long and hard answer is about a book's length in size and might well be more.
As to data, there are several "official" series, IIRC from NASA, from NOAA, and from the Hadley Centre. See e.g. this. Data is freely available, so you can plot your own.
However I don't know why there is controversy over the existence of hiatus if even the IPCC 2013 report accepts it as existing and spends a few pages (Ch. 9) discussing it.
Science moves on... are you suggesting that just because it was in the IPCC report the matter is fully settled and over with? Even though I agree with the conclusions of the IPCC report, I'm sure there are many things in the report which will have to be revised in the future.
Just like gjm, I think you're confusing existence and interpretation.
Outside of political posturing, I don't know why someone would claim that hiatus as a feature of the historical data set does not exist. It does and it's pretty clear. That's existence. What does the hiatus mean is a different and a much more complicated question. You can claim it's just an artifact of random variation. You can claim it reflects multi-year cycles in global climate patterns. You can claim it shows that our models are deficient and we don't understand climate variation. You can claim many things -- but a claim that the hiatus just does not exist doesn't seem reasonable to me.
Not sure why you're using this unusual terminology, but I'm arguing about what you call existence. It seems that you're arguing that the 'hiatus' exists with either absolute certainty (in which case you'd have to provide a logical proof) or at least with very high likelihood. However, I see no reason we should assign a very high likelihood to its existence.
The 'existence' of a 'trend' or 'hiatus' in general time series data is part of the map, not the territory. If the climate temperature data were just a smooth line (like this - graph not relevant to the discussion) then I'd agree with you, but it's not. It looks like this.
What's unusual about my terminology?
I am not sure about that. In your "smooth line" example, is the trend part of the map or the territory? More generally, what can I say about a time series that you would consider to be territory and not map?
Oh, and if you want to be technical about it, the time series you're looking at is not part of the territory to start with. It's a complex model-dependent aggregate.
If the temperature graph looked like the first graph, then inference of a trend (which is, again, part of the map) with high probability might be made. But it does not look like that.
That f(t) = x.
For the sake of discussion of the existence of a hiatus I'm assuming the temperature graph is a given. But you're right in that the big picture is that the temperature graph itself is not part of the territory.
In this case I am not sure what do you mean by "exists".
Can you give a definition, preferfably a hard one, that is, an algorithm into which I can feed the time series and it will tell me whether a particular feature (e.g. a hiatus) exists or not?
http://www.nature.com/articles/srep16784
Lewandowsky has an... interesting reputation.
If there's something wrong with the article, it seems like you should be able to say what it is rather than making insinuations about one of its authors.
(Lewandowsky is strongly disliked by those whose position on global warming differs from the mainstream scientific consensus, no doubt. So far as I can tell he doesn't have a reputation for dishonesty or incompetence among groups without a strong motivation to put him down.)
I haven't read the article, just glanced at the front page, saw the name of the lead author and thought "Hmm... that name looks familiar".