Six Sigma Deviation for Antarctic Sea Ice
44 points by rene_d 1 year ago | 32 comments- kuhewa 1 year agoIt's clearly a signal of ongoing warming, but the assumption of a Gaussian probability distribution of annual ice extent- something we only have a few tens of years of data to estimate - seems peculiar.
- harperlee 1 year agoI’m not a statistician, but I’ve read somewhere the argument that the gaussian is the distribution that assumes the least about its data (just that there’s a mean and non-infinite variance) so it is typically safe to use when you know little about the real distribution.
(I’m just commenting to compel someone to correct me and expand on this subthread really :) )
- kuhewa 1 year agoGood tactic!
> so it is typically safe to use when you know little about the real distribution.
That was what the quants doing risk assessment at the big banks thought pre-2008, which is the other context I associate with the n-sigma notation for probability
- carlmr 1 year agoSo what OP is missing is the central limit theorem[1]. According to which any sum diatribution of independently-identically-distributed random variables in the limit becomes gaussian distributed.
So taking it apart, given some restrictions, any sum of randomly distributed data is gaussian distributed.
If you take an average of some value. E.g. sea ice extent at fixed date x, e.g. January 1st every year, you have a sum distribution.
So you're not talking about the random distribution of any date, but of the random distribution of the average value. Only this has the Gaussian distribution.
Now there are some restrictions IID - independently identically distributed. This is the part the quants got wrong. Identical distribution is usually not the issue, we can, for a certain timespan, assume that the random distribution stays roughly the same.
But independent was the issue. If one event is correlated with the next, the central limit theorem may hold for a bit, but if the correlation is, too extreme will break down, like in the quant models of yore.
Their estimates for the housing market risk were ok as long as the credit defaults were not highly correlated, but as soon as the crisis started some vicious cycles formed between the foreclosures and tumbling house prices causing more foreclosures.
The models broke down.
Back to the ice sheats, if we assume the melting of the ice sheats won't increase (or decrease) the melting of the ice sheats we're good. I don't know about causative mechanisms here, but it could be that the models do break down in these times of extreme change.
That doesn't mean that the extreme change is nothing to worry about, since only by being extreme might it break the models.
- carlmr 1 year ago
- kmmlng 1 year agoMaybe you can make an argument that, in the absence of any information, your best bet is assuming a Gaussian distributon, but it definitely is not safe to assume so. Your data might not be symmetrically or even unimodally distributed and making these assumption can lead to completely wrong conclusions.
- joe__f 1 year agoIf you know that your data has a well-defined mean and standard deviation but you know nothing else about it then you start with a Gaussian distribution. This isn't an assumption. The Gaussian distribution has the highest entropy and hence encodes the least information possible about the data. Then as you learn more about your data, you would update this distribution using Bayes' theorem. This could give rise to skew or multiple maxima.
- joe__f 1 year ago
- cozzyd 1 year agoIn this case, as each day is highly correlated to the previous one, it is safe to say that the distribution of daily sea ice variation is probably not Gaussian? (Though obviously, this is very bad...)
- evandijk70 1 year agoThe comparison is between ice extent measurements at the same date, at differing years, so the day-to-day correlation is not the relevant metric here, but the year-to-year correlation, which should be very low.
- evandijk70 1 year ago
- kuhewa 1 year ago
- defrost 1 year agoThirty years of antartic sea ice extent varied in a Gaussian fashion - with a fairly tight std deviation.
The last few years have been further and further from the [1981 - 2010] "normal flux cycle".
This may help visualise the data better:
https://nsidc.org/arcticseaicenews/charctic-interactive-sea-...
( click the antartic button to switch poles; the default is to grey the thrirty year normal data band and to only show last year and this year, other choices can be made by selection on the data table )
- harperlee 1 year ago
- junon 1 year agoSo we're fucked at this point, and nobody is saying anything about it.
Don't Look Up was right. We're dumb idiots of a species.
- rf15 1 year agoThe fun thing is, we cannot recognise this kind of danger. Our regular animalistic detection mechanism cannot be triggered by this, so we're kind of aware but nothing in us tells us to get away from the problem. Even as you write this, you probably don't truly believe that this could very well be the end. For once the slowly boiled frog thing is actually true.
- junon 1 year agoI certainly have had my panicky days about this, so something inside me is getting at least part of the picture.
Unfortunately the people who can actually do anything about this lack the parts of their brain that could ever hope to understand.
- 11235813213455 1 year agoover 20 years I completely recognized a warming, and I'm doing my best (no car, minimal consumption/spending, CO2eq footprint about 5% of average person in Western Europe), not many people are doing this, but there are plently benefits, not just environmental
- hotpotamus 1 year agoIt seems a bit like dying of a radiation overdose - a lethal exposure can take just moments, and you will go on as though nothing happened for a time, but the damage is done and irreversible.
- 11235813213455 1 year agolike cigarettes, another dumb behavior of humans
- 11235813213455 1 year ago
- junon 1 year ago
- noneoftheaboveu 1 year agoIt’s noneoftheabove that stands above the don’t look up.
- rf15 1 year ago
- balnaphone 1 year agoPractically speaking, unverifiable and unfalsifiable.
They say once in 7.5 million years, so why don’t they show the previous 7.5 million years?
If that's not possible, and we only have 1989-2023 data, then the 7.5 million year comment is particularly ridiculous, as is making any generalization with data for only 0.0001% of the time span in question.
- BobbyJo 1 year agoThe timespan is just a more easily digested framing of the odds. It's meant to be easier for a layman to understand, and doesn't actually have anything to do with what things would look like over 7.5 million years. That would take models with an impossible level of detail about planet scale dynamics.
- BobbyJo 1 year ago
- defrost 1 year agoThe quote from one researcher here:
Antarctic sea ice levels dive in 'five-sigma event' (abc.net.au)
https://www.abc.net.au/news/2023-07-24/antarctic-sea-ice-lev...
34 points by adrian_mrd 1 day ago https://news.ycombinator.com/item?id=36839757
has it a bit over five sigma and easily less than six.
Still hella significant.
- dredmorbius 1 year agoI want to make clear up front that I take global warming absolutely seriously, that it is undoubtedly human-caused, and that it is progressing faster than consensus models have predicted.
But the interpretations given to 34 years of highly-correlated time-series data are highly questionable and largely unwarranted.
Put briefly, we have very little long-term global remote-sensing data largely because remote sensing didn't exist until the 1960s, and largely came of age long after then. As with this data series which begins in 1989.
We *ABSOLUTELY DO* have many other long-term data series showing tremendous changes and associated climatic conditions: ice-core data going back 800,000 years, sea-level measurements going back a billion+ years (at which point plate tectonics are a major confounding factor), plant growth distributions and patterns dating back millions of years, and global temperature inferences also dating back on the order of a billion years or more.
And yes, assuming a normal distribution, a six-sigma event is extraordinarily rare. But to make accurate inferences of such extreme-outlier events based on 34 measurements is statistical malpractice.
Call this "unprecedented in the data record". Call it "extremely concerning". Find other data series with which this pattern can be correlated and from which stronger inferences might be drawn.
(Note that ice-field extant data before the age of satellite observation are very thin, though outlier events such as bergs being sited in temperate waters might well occur, and that shipping logs do tend to record numerous events of interest and date back about 500 years over a fairly wide area. Indigenous records from, say, Tierra del Fuego might also note sitings over a longer period.)
Sources: three years of stats courses at uni, work in stats and data reporting professionally and at an amateur level, though not an actual statistician.
- HocusLocus 1 year agoWell bite me for not chiming in with some rehash of the Earths-heating-be-very-afraid greenhouse dogma, but specifically
( https://www.nature.com/articles/s41598-022-05449-8 ) Persistent extreme ultraviolet irradiance in Antarctica despite the ozone recovery onset ?
That is an Earth change I could sink my teeth into because our measurements of ozone are first rate, the crisis continues and Antarctica is a known target of the phenomenon.
- 11235813213455 1 year agoWhere are those persons saying that with global warming Antarctica would actually get cooler?
- roflyear 1 year agoIt is incredibly easy to bash something, very hard to come up with your own ideas.
To show this, reader, try to do a small experiment yourself - something your interested in - but make it really, really small. Can be testing products you use often to see which is the best for you.
It is REALLY hard! And it's extremely easy for people to pick it apart. "Oh, you know more than the guys who wrote the standards?" "I've been using that for years, you're just using it wrong" "Here's a picture of me doing xyz it works fine"
They spent two seconds, you almost certainly spent days and days on your really small test.
This is why you won't see people back up these claims. They didn't spend time or effort getting there, and they won't spend that time or effort backing them up.
- roflyear 1 year ago
- RyanAdamas 1 year ago[flagged]
- defrost 1 year agoIn order to melt ice of 0°C to water of 0°C, a high amount of energy is needed, equivalent to 334 Joules for each gram, this is latent heat.
The specific heat of water is 4.190 J/(g°C). It means that it takes 4.190 Joules to heat 1 g of water by 1°C.
The same energy that melts 0°C ice to 0°C water will raise 0°C water to 79.7°C which is more than three quarters of the way to boiling.
We're facing higher and higher amounts of trapped energy as a result of increasing thermal insulation from CO2 ( and more and more from methane and water vapor ).
While we have large amounts of ice as a buffer that energy has a sink that won't drastically* raise near surface tempretures.
As the ice caps dwindle more and more energy goes towards greater and greater rates of tempreture increase.
- rcarr 1 year agoUsername checks out
- RyanAdamas 1 year ago[flagged]
- rcarr 1 year ago
- mschaef 1 year ago> It boggles my mind that a warm blooded creature that needs arable land would be upset about icecaps melting.
The earth is a large system with lots of inertia. When some aspect of it changes relatively quickly, it's natural to be uneasy. Particularly when the downstream consequences of that change are already becoming visible.
To wit CO2 levels over the last 1my.
https://www.epa.gov/climate-indicators/climate-change-indica...
The notion of increased CO2 leading to higher atmospheric heat capture dates back to at least 1856:
https://static1.squarespace.com/static/5a2614102278e77e59a04...
So the combination of well-established science connecting CO2 to atmospheric heat, a relatively massive increase in CO2, and the emergeng changes predicted by a atmospheric heat increase - that is a valid reason for concern.
> We want the poles to be livable.
If it was possible to make this happen in isolation, maybe it would be a desirable goal. Given that this is not possible, it has to be viewed in context of the costs it also imposes. More severe weather is part of it, but also loss of both coastline due to sealevel rise and inland areas that become unlivably hot or newly unsuitable for agriculture.
> These changes are absolutely unpredictable and the models these researchers use are so heavily interlinked and layered one small mistake in the foundational data can skew the entire output. Almost as if thats how you lie with statistics...
Here you make the other sort of error - the error where you throw up complexity as a smokescreen to distract from the potential need to take action. If you're waiting for a complete set of totally accurate predictive models before you're willing to take action, you'll be waiting for a long time.
> Even so, I want Greenland to be habitable within the next 100 years. Even at the expense of coast line.
Have you consulted the people that live on the coastline? It doesn't take a whole lot of sea level rise before you're displacing hundreds of millions of people. (Not to mention the other associated costs of higher atmospheric energy.)
- RyanAdamas 1 year ago[flagged]
- mschaef 1 year ago> as opposed to your faith in hubristic science? science that has been bought and paid for time and time again for big money interests? are those just red herrings and whataboutism as opposed to 'learn from history or repeat it'? you're using corporate science to justify arrogant status quoian perspectives.
I expressly linked to experimental science dating to the 19th century. Not sure how that qualifies as 'corporate' or 'big money' science. There are other extant discussions of the subject that predate the influences you mention.
If you're claiming bias in the other figures (the increase in CO2 or the temperature numbers), then it should be possible to produce counterexamples and more formal rationales about why they make sense.
> > people who live along the coastline
> you mean the millionaires who are constantly pushing the global warming myth?
No. Just to pick a counterexample, Bangkok's elevation is 5 feet above sea level, and it's a city with ~10MM people. Lots more likelihood of catastrophic impact there than the US 'coastal elite' you seem to be alluding to.
- roflyear 1 year agoDo you have stake in the game? If you are wrong about this, will you take responsibility?
The wager is: we try to do the conservative thing by reducing emissions. The side effects are positive, anyway, since it will also reduce pollution.
The other side of this wager is, we do nothing: and the potential is catastrophic for everyone.
Doesn't it seem like a silly gamble?
- mschaef 1 year ago
- RyanAdamas 1 year ago
- roflyear 1 year agoIs this sarcasm? Almost impossible to tell. I think it isn't.
- defrost 1 year ago