Average global temperature

Discussion in 'Earth Science' started by vhawk, Mar 2, 2009.

1. TrippyALEA IACTA ESTStaff Member

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You idiot. In other words, you're simply going to avoid the topic, because you have no argument.
I'm well aware of the assumptions, I've even expounded on some of them for you.

And you're right, you're analogy is absolutely useless. Nobody who knows anything about statistics actually believes that there are people out there with 1.5 cars, and 2.4 children.

More to the point, have you read your own source?
the argument comes down to this:
Which i've already stated I agree with, but don't think is neccessarily relevant.

In short, that paper raises many of the things that i've already mentioned, even some of the concerns i've expressed (not neccessarily to you, but that's whta you get for making assumptions), and as far as the deomstration with the coffee and the iced water goes, all that really demonstrates is the importance of choosing the correct statistic. I would also argue that that particular example is a really bad example, because how you define the system is also critically important. That example compeltely ignores the room, and only looks at the various averages of the two cups, when anyone with two braincells to rub together (which, admittedly might exclude you) can see that the cups aren't reaching equilibrium with each other, but they're reaching equilibrium with the room, and the averages of the cups are not representative of the averages of the system. So they've looked at bad measures, and compared bad measure to good measures, and they've poorly defined the system that they're taken the averages of, and on the basis of those bad choices, come to the conclusion that the original idea is meaningless.

Anybody who's actually studied statistics knows that not all measures of the center of the data are equally valid for all systems. Some can give false impressions and indicate false trends.

That's the simple fact that you seem to have lost site of - is that an average is 'simply' a measurement of the center point of the data.

To use their example, the Harmonic mean of the temperature of the two cups is genuinely pretty much meaningless. The temperature at a location on the earths surface tends to pretty much follow a normal curve, but the harmonic mean is really only useful in a log normal distribution. The Harmonic mean is calculated by taking the nth root of the product of the individual data points (nothing to do with sums at all). This is equivalent, however to taking the average of the logs of the data points, but this is only useful when dealing with something that varies over several orders of magnitude, which temperature doesn't.

So saying that because the harmonic mean decreases while the simple mean decreases the idea of applying a mean to temperature is meaningles, is quite simply, a logical fallacy (in part because no sane statistician would try and apply a harmonic mean to temperature, because it's the wrong mean to use).

Something similar can be said for the Root Mean Square, which is calculated by squaring the data points, taking their average, then taking the square root of that. RMS gets used where the simple average would be zero - for example, the simple average of the voltage in the mains line is 0 volts. Does that mean I think it's safe to shove a fork in the plug, because on average, there's no voltage in the lines, so surely it must be safe. So again, they've used the wrong measure, and claimed because it disagrees, the idea of a mean temperature is wrong.

They say it's precedented, but that doesn't mean it's appropriate.

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3. SyzygysAs a mother, I am telling youValued Senior Member

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You idiot (since we are friends now) I asked for a value in Fahrenheit or Celsius not for an explanation.

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I asked for the fluctuation DURING the year. Now I tried to find it, but so far I haven't. My guess is that the difference is very little, probably a few Fs....

Might be?? We either do know it or we don't.

As an engineer I call this utter bullshit! Specially not down to the decimals...

Now the chart showing temperature by month, that was a special locality, and not the global correct? So is there a similar chart for the global average?? Because that's what I have been asking about.

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5. SyzygysAs a mother, I am telling youValued Senior Member

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Last edited: May 9, 2009
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7. TrippyALEA IACTA ESTStaff Member

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Sorry, I forgot engineers were unable to deal in generalities.

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Again, the GLOBAL MEAN ANNUAL TEMPERATURE doesn't fluctuate during the course of a single year.
It represents the average of the fluctuations over the course of a year, across a number (or all) localities.

Again, in this instance, I was talking about specific locations. I think, for example, based on that graph, in Orlando, the average temperature in January is different from the average temperature in September, but, it's not neccessarily that way everywhere.

Correct.

I have no idea, and I've never looked, I don't see much point at looking at timescales less than a year, because then you start getting seasonal variations come into it (for example, I imagine that the Global Mean Temperature for the month of December is going to be different from the Global mean temperature in July, because in December the Earth is closer to the sun, and it's summer in the Northern Hemisphere, where most of the land mass is - so the data starts becoming useless).

8. iceauraValued Senior Member

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It shows a steep upward trend for a century, totaling more than a full degree C in the past hundred years (a time frame which happens to begin at a low spot). If that trend continues life is going to be very different in a generation or so, for us agricultural humans.

9. SyzygysAs a mother, I am telling youValued Senior Member

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Yeah right, steep. Otherwise known as statistical noise.

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Since we don't have any record from previous centuries, we don't know if 1 C variation is normal or trendy.

10. SyzygysAs a mother, I am telling youValued Senior Member

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This is the first time you mention this, and finally I figured it out by myself too. I still asked for a numeric value, which is I think 14.7 C or so....

OK, so I will summarize what I have learnt from the net:

Measuring the global average temperature is so complex and not yet standardized task, that so far reliable data is hard to find. It is also questionable just how meaningful this data would be. Not to mention that historical data is rare if we go beyond 150+ years in time and obviously it only comes from big cities, so we have no idea how far away places' temperature varied through history.

Another point is that historically temperature is measured where humans live, which is big cities most of the time. Now anyone know that cities tend to rise the temperature of the locality for various reasons. So the "steep" increase in the last century could attributed to this or simply just statistical noise....

11. TrippyALEA IACTA ESTStaff Member

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Sounds about right, yeah, about 15°C - something you can calculate to remarkable accuracy, by treating the earth as a grey-body, and the emissivity of the atmosphere.

OK, so I will summarize what I have learnt from the net:

Measuring the global average temperature is so complex and not yet standardized task, that so far reliable data is hard to find. It is also questionable just how meaningful this data would be. Not to mention that historical data is rare if we go beyond 150+ years in time and obviously it only comes from big cities, so we have no idea how far away places' temperature varied through history.[/quote]
I would contend this statement.
Firstly, as I said, we do have reliable proxies that date back much further than that - for example δO-18. It's been possible to determine regional and global average temperatures back millions of years.

The first part of this is correct, however it is also something that can be accounted for, whether or not it's accounted for correctly is another matter entirely.

The second part, well, it's all too easy to dismiss any trend as statistical noise, but doing so may be a mistake. I could, if I wanted to, prove that chocolate causes car accidents, as long as I was willing to ignore a couple of lurking variable.

The point here is that what we're observing fits with what we expect (at least to some extent) based on the physics of the situation (Simple harmonic motion, and the stefan boltzman distribution, to name a ocuple of things) and the physics of the situation, and it's implications were first recognized about 120 years ago.

12. SyzygysAs a mother, I am telling youValued Senior Member

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1. We don't know just how accurate they were.

2. There is a huge difference apparently between 2-3 C, so saying that the average temperature in Siberia in the 15th century was between 10-15 C is not going to cut it, not to mention is that really meaningful?

3. If we really could do that, why can't we have a temperature timeline going back let's say 2000 years? Because it can not be done and not accurate in any meaningful way.

But if you know such a timeline, please post the link, because I am curious how average changed over the last 2 milleniums...

Between 1945 and 1975 according to the chart the average temperature DROPPED 0.6 C. So if this conversation took place in 1975 we would be talking about global cooling.

Now personally I accept that what humans have done in the last 150 years have a mostly warming effect on the globe, but my point is that measuring it is way more complex and historically missing then what the average media news makes us to believe...

13. TrippyALEA IACTA ESTStaff Member

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Actually, we do.
If we talk ice cores, for a moment, then the δO-18 in that ice has a strong relationship to the temperature at the time the Ice was precipitated.
Water containing δO-18 is heavier, therefore takes more energy to evaporate.
The higher the δO-18, the higher the temperature.
You can also do a δO-18 analysis on fossils containing calcite for much the same reason.
And these are relationships that can be measured in labs, and confirmed in the field over the last 150 years.
The reason why I say that δO-18 is dependent on averages is because as the water vapour moves north and cools, O-18 is the first to condense out.

Not really sure what you're asking here, and I doubt Siberia was ever that warm

Let's assume you're right here, and the variatrion between different reconstructions has nothing to do with different ice core locations, then this is why people focus on averages, and also focus on the last 150 years.

Last 2000 years:

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Last 12,000 years:

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What the colours mean: http://commons.wikimedia.org/wiki/File:2000_Year_Temperature_Comparison.png
In fact there was discussion of global cooling in the '70s. The rationale behind it, was essentially it was known that particulates and aerosols reflected sunlight back into space before it had the opportunity to really interact with the earth, or the atmosphere, thus reducing the total insolation at the earths surface. Because the aerosols and the particulates were reflecting the light back into space before the green house mechanism had the opportunity to store the energy, there was concern that continued pollution might drive the planet into an ice age in spite of the increase in CO2.

Even modern models take this effect into account.

Perhaps, which is why I generally endeavour to find the original release that was made by NOAA, or NASA or whoever to the media, so I can cut through the personal spin, mis understandings, and general bullshit.

The key point to remember here is that the media aren't scientests, and what is said by the media isn't always a direct reflection of what's said to the media.

As far as many of your points you're raising go, while they may have some validity, they're also things that you get taught in first year statistics.

14. iceauraValued Senior Member

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We have error range estimates that put them within meaningful and informative probabilities. Welcome to science in the real world.
I see nothing like that on any chart -certainly not the one you posted above. The entire range on that chart between '45 and '75 is about .1C at most, and the temp in '75 was about average for the period - not cooling.

But it was true some people were worried about the cooling phase of the Milankovitch cycle, and the likelihood that we are in the cooling phase of our current interstade. That worry did not come from the recent data, but from the overall paleontological situation - as soon as the data started coming in, the worries changed. We will have plenty of time to worry about the slow coming of the next glaciation centuries from now, if we get through the next couple of hundred years in decent shape.
The past several thousand years of continent scale temperature variation are pretty well established to informative accuracy in several different and mutually supportive ways.If you were really curious, a five minute net search would have handed you hundreds of articles, publications, data analyses, and so forth. Since you haven't bothered, I will content myself with a few links to the tree ring and coral stuff, and leave you in your burning curiosity to discover the diatom, pollen, ice core, rainwater and atmospheric gas isotope, document search, ecological residue, grological and solar traces, and various other forms of evidence and argument on your own:

http://www.climateaudit.org/?p=4783
http://www.legos.obs-mip.fr/~delcroix/PDF_PUBLICATIONS/Correge_etal_GRL_2001.pdf
http://www.sciencemag.org/cgi/content/full/295/5563/2250/DC1
http://rivernet.ncsu.edu/courselocker/PaleoClimate/Jacoby & Arrigo 1997 Tree Rings.pdf
http://www.springerlink.com/content/h685450m553x885x/

If you want to argue about the media presentations, you will find Trippy far more amenable to your point of view. You will also find yourself in need of much different arguments. You are arguing against the science, at the moment, from a pov that appears to be mostly informed by that media you claim to object to. "No such thing as an average global temperature" is talk radio crapola.

15. SyzygysAs a mother, I am telling youValued Senior Member

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Interesting, but Trippy did. Post #103. Between 1944 and 1956 the temperature dropped .6 C, now THAT is steep...

The chart what Trippy posted also shows temperature drops of 1 C in medevial times. The point is here that one doesn't need to shit himself when the temperature changes by 1 C.....

Also,because I am the curious type, would you mind telling me the average annual temperature in Siberia in 1500... I have always wondered about that..

Sure. And if the error range is 1-2 C, than 1 C change is way inside the range.

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Last edited: May 11, 2009
16. TrippyALEA IACTA ESTStaff Member

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Actually, I didn't comment on the trend that you mentioned, I simply commented that there had in fact been discussions of global cooling in the 70's. Although I can see how you might read that to confirm your comments on the trend.

I should also point out that you're only looking at one part of the trends.
Sure, the temperature may have warmed by up to 1k in the medieval period, but look at what it was warming up from, and how long it took.

Then compare that, on the same graph, to what's happened since 1800 - that's why climatologists are concerned (well, one of the reasons anyway).