Here’s an interesting Q&A on issues with trying to determine the SAT of the Earth that I have not seen before. There’s a surprise at the end as to who wrote it.
Q. What exactly do we mean by SAT ?
A. I doubt that there is a general agreement how to answer this question. Even at the same location, the temperature near the ground may be very different from the temperature 5 ft above the ground and different again from 10 ft or 50 ft above the ground. Particularly in the presence of vegetation (say in a rain forest), the temperature above the vegetation may be very different from the temperature below the top of the vegetation. A reasonable suggestion might be to use the average temperature of the first 50 ft of air either above ground or above the top of the vegetation. To measure SAT we have to agree on what it is and, as far as I know, no such standard has been suggested or generally adopted. Even if the 50 ft standard were adopted, I cannot imagine that a weather station would build a 50 ft stack of thermometers to be able to find the true SAT at its location.
Q. What do we mean by daily mean SAT ?
A. Again, there is no universally accepted correct answer. Should we note the temperature every 6 hours and report the mean, should we do it every 2 hours, hourly, have a machine record it every second, or simply take the average of the highest and lowest temperature of the day ? On some days the various methods may lead to drastically different results.
Q. What SAT do the local media report ?
A. The media report the reading of 1 particular thermometer of a nearby weather station. This temperature may be very different from the true SAT even at that location and has certainly nothing to do with the true regional SAT. To measure the true regional SAT, we would have to use many 50 ft stacks of thermometers distributed evenly over the whole region, an obvious practical impossibility.
Q. If the reported SATs are not the true SATs, why are they still useful ?
A. The reported temperature is truly meaningful only to a person who happens to visit the weather station at the precise moment when the reported temperature is measured, in other words, to nobody. However, in addition to the SAT the reports usually also mention whether the current temperature is unusually high or unusually low, how much it differs from the normal temperature, and that information (the anomaly) is meaningful for the whole region. Also, if we hear a temperature (say 70°F), we instinctively translate it into hot or cold, but our translation key depends on the season and region, the same temperature may be ‘hot’ in winter and ‘cold’ in July, since by ‘hot’ we always mean ‘hotter than normal’, i.e. we all translate absolute temperatures automatically into anomalies whether we are aware of it or not.
Q. If SATs cannot be measured, how are SAT maps created ?
A. This can only be done with the help of computer models, the same models that are used to create the daily weather forecasts. We may start out the model with the few observed data that are available and fill in the rest with guesses (also called extrapolations) and then let the model run long enough so that the initial guesses no longer matter, but not too long in order to avoid that the inaccuracies of the model become relevant. This may be done starting from conditions from many years, so that the average (called a ‘climatology’) hopefully represents a typical map for the particular month or day of the year.
Q. What do I do if I need absolute SATs, not anomalies ?
A. In 99.9% of the cases you’ll find that anomalies are exactly what you need, not absolute temperatures. In the remaining cases, you have to pick one of the available climatologies and add the anomalies (with respect to the proper base period) to it. For the global mean, the most trusted models produce a value of roughly 14°C, i.e. 57.2°F, but it may easily be anywhere between 56 and 58°F and regionally, let alone locally, the situation is even worse.
Source is here
h/t to: Nick Boyce
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“richardscourtney says:
August 15, 2013 at 1:32 am
You are absolutely correct. However, its even worse than that. Given the fact that 7/10’s of the surface does not have a thermometer anywhere near it so a “global average” is even more meaningless than you state. Here in Australia, the BoM/CSIRO developed a new way to calculate a nationwide average and similarly with GISS and HadCRU, don’t identify their data, sites, measurements, adjustments nor their methods. Of course, the average generated is splashed across newscasts on TV, in “angry” red, as being the highest evah!
Put it simply – it’s a mess. But what a surprise who said it!
<bReply to richardscourtney, August 15, 2013 at 1:32 am
Richard,
You are right!
But these days to be right is not enough: when climate issues are reduced to only one parameter – temperature – we are stuck with this physical and societal nonsense.
And everyone has an opinion on temperature…
According to GISTEMP’s version 3 of station data
http://data.giss.nasa.gov/gistemp/station_data/
there are two weather stations at Amundsen-Scott at the south pole. They have a continuous record since 1957, apart from a gap of one year for one of them. Taking into account this break, the average temperature, 1957 to 2012, at one of them was -48.4°C, and -49.4°C at the other. So even after GISTEMP’s “homgenisation” (whatever that may mean), there’s still a difference of 1°C for two weather stations at virtually the same location. Both are at 90.0°S, 0.0°E. Presumably, because of the prestigious location, both stations are properly equipped and well maintained. I’m just an old fool who knows knows ****** about ****** all, but it seems to me that if we know the temperature at Amundsen-Scott to no better than (+/-(0.5))°C, the margin of error is bound to be greater than that for an estimate of global surface temperatures, even if we employ temperature anomalies. Temperature anomalies are inferred from absolute temperatures, or they’re inferred from nothing at all. As it happens, I have a deep loathing for temperature anomalies. They conceal at least as much as they reveal. They are a degraded form of information. From absolute temperatures you can infer as many temperature anomalies as you please until the cows come home. But it doesn’t work the other way about
The major thing that Gavin and the other “climatologists” don’t seem to realize, is that if you have a meaningless, undefined quantity, then the anomoly calculated from that meaningless undefined quantity is still MEANINGLESS and UNDEFINED.
davidmhoffer writes “The notion of anomalies in cold regimes being averaged with anomalies from warm regimes is absurd.”
Which is why estimations of energy content, specifically the ocean heat content, are much better measures of global warming. Gavin may be correct and candid about SAT but when it comes to comparing the OHC from the models to the measured OHC he shows his true “team” colours.
For years now he has refused to make a true comparison in his annual “comparison of models vs reality” that happens early in the year. Instead he extrapolates what the models might have done rather than simply working out what they did do. Apparently understanding this measure isn’t worthy of his time.
Steven Mosher says: August 14, 2013 at 2:45 pm
“For example we have 39000 stations.”
No, you don’t. Show me your list of 3900 stations for 1880.
A few points of interest as a follow on from the Q&A.
1. The convention for surface temperature is to use 1.5m temperature, as this is at a height where the thermometer is easy to read without stooping down or climbing a ladder.
There are some oddities with this. I’ve seen 2m temperature quoted in a few places, though I’m not sure where that comes from. Also, for the global temperature averages the 1.5m temperature over land is often combined with the sea surface temperature (SST), which is generally the temperature of the top layer of the ocean water, rather than the air 1.5m above it.
Finally, most models do not have a level at 1.5m above the surface – the lowest level will be typically somewhere like 5-20m above the surface. Obviously some sort of algorithm is used to convert the lowest level temperature in the model to the 1.5m temperature.
2. The Q&A is absolutely right to say that calculating a daily mean is fraught with complications, but this is the sort of thing that averages out in a global mean. I did a comparison with model data between a daily mean over all timesteps and a daily mean = (max + min) / 2 and locally the differences could be very large. In the global mean, nothing.
The only potential pitfall here is if you compare observational data calculated in one way with model data calculated in another.
Alistair Ahs:
You conclude your post at August 15, 2013 at 9:02 am
http://wattsupwiththat.com/2013/08/14/the-elusive-absolute-surface-air-temperature-sat/#comment-1390845
saying
NO! You are plain wrong.
If the so-called “observational data” is meaningless then it cannot be modeled by a true model of the Earth’s real climate. And it is meaningless.
Please read my above post at August 15, 2013 at 1:32 am
http://wattsupwiththat.com/2013/08/14/the-elusive-absolute-surface-air-temperature-sat/#comment-1390605
and all of its link which I copy to here
http://www.publications.parliament.uk/pa/cm200910/cmselect/cmsctech/memo/climatedata/uc0102.htm
Richard
How does one average a temperature?
What is the average temp of a cup of nearly boiling hot water next to a glass of ice cubes?
Does said average say anything important about the system?
If so, what?
If not, why take it at all?
Max™ :
re your post at August 16, 2013 at 2:48 am.
As you say, ‘average global temperature’ is a meaningless metric.
But it can be compiled in any way one wants, so it can show whatever one wants to be shown.
This meaningless and undefined nature of ‘average global temperature’ makes it politically useful. I explain the usefulness as follows.
Governments need to raise taxes, but people do not want to pay taxes.
So, politicians desire a tax that people want to pay. The UK has one such tax. i.e. the National Lottery.
Failing to obtain sufficient taxes people want to pay, then politicians desire a tax that nobody would object to paying. And who could object to a tax (e.g. a Carbon Tax) intended to save the planet for our children and our children’s children?
Hence, governments pay so-called “scientists” to determine ‘average global temperature’.
I hope this is sufficient answer to your questions.
Richard
Hey Mosher, where are those 39,000 weather stations for 1880?
“Sleepalot says:
August 16, 2013 at 5:56 am”
No! It’s worse than that. It’s X number of stations that have “measured” global land AND sea “average” temps since 1880.
Well yes, it’s both: if you change the particular stations, and/or change the number of stations used you make yearly averages incomparable, and the “series” is a work of fiction.
Where’s Mosher? Did he run away?
Sleepalot says: @ur momisugly August 15, 2013 at 8:49 am
Steven Mosher says: August 14, 2013 at 2:45 pm
“For example we have 39000 stations.”
No, you don’t. Show me your list of 39000 stations for 1880.
>>>>>>>>>>>>>>>>>>>>>>>
Actually it is much worse than that.
Jo Nova, May 21, 2010 The Great Dying of Thermometers
ChiefIO, Febuary 2, 2010 Zombie Thermometers – Return of The Un-Dead: In looking for what thermometers died in 2010, I discovered that there are Zombie Thermometers. They appear to be alive in some years, but sometimes are unresponsive and give no data.
On top of that the actual sample size is ONE since you are measuring a unique location at a unique time without duplication.
This means the error bars are at least +/- 0.5 to 1°C link