This new paper by Dr. Ross McKitrick of the University of Guelph is a comprehensive review of the GHCN surface and sea temperature data set. Unlike many papers (such as the phytoplankton paper in Nature, complete code is made available right from the start, and the data is freely available.
There is a lot here that goes hand in hand with what we have been saying on WUWT and other climate science blogs for months, and this is just a preview of the entire paper.This graph below caught my eye, because it tells one part of the GHCN the story well.
1.2.3. Growing bias toward lower latitudes
The decline in sample has not been spatially uniform. GHCN has progressively lost more and more high latitude sites (e.g. towards the poles) in favour of lower-latitude sites. Other things being equal, this implies less and less data are drawn from remote, cold regions and more from inhabited, warmer regions. As shown in Figure 1-7, mean laititude declined as more stations were added during the 20th century.
Here’s another interesting paragraph:
2.4. Conclusion re. dependence on GHCN
All three major gridded global temperature anomaly products rely exclusively or nearly exclusively on the GHCN archive. Several conclusions follow.
- They are not independent as regards their input data.
- Only if their data processing methods are fundamentally independent can the three series be considered to have any independence at all. Section 4 will show that the data processing methods do not appear to change the end results by much, given the input data.
- Problems with GHCN, such as sampling discontinuities and contamination from urbanization and other forms of land use change, will therefore affect CRU, GISS, and NOAA. Decreasing quality of GHCN data over time implies decreasing quality of CRU, GISS and NOAA data products, and increased reliance on estimated adjustments to rectify climate observations.
From the summary: The quality of data over land, namely the raw temperature data in GHCN, depends on the validity of adjustments for known problems due to urbanization and land-use change. The adequacy of these adjustments has been tested in three different ways, with two of the three finding evidence that they do not suffice to remove warming biases.
The overall conclusion of this report is that there are serious quality problems in the surface temperature data sets that call into question whether the global temperature history, especially over land, can be considered both continuous and precise. Users should be aware of these limitations, especially in policy sensitive applications.
Read the entire preview paper here (PDF), it is well worth your time.
h/t to E.M. Smith
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It should be noted that “GHCN” stands for “Global Historical Climatology Network,” which is managed by the National Climatic Data Center, Arizona State University and the Carbon Dioxide Information Analysis Center of the U.S. federal Department of Energy.
I confess to having flashed on “growth hormone” and “cyanide,” but that shows you how limited is the perspective of somebody skilled in sigmoidoscopy.
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You’re right, very interesting:
“Section 4 will show that the data processing methods do not appear to change the end results by much, given the input data. ”
That’s the funniest thing I’ve read for a while. Thank god we have professors of economics to explain science to us.
I look forward to the blanket coverage in tomorrow’s media.
Even more persuasive is Fig 1-10 showing “Changes (“delta”) in the global average temperature resulting from GHCN adjustments”.
Quoting from the report:
“There are two notable features of the graph. The first is that the adjustments are mainly negative prior to 1940 and positive up to about 1990, effectively “cooling” the early part of the record and “warming” the later record. In other words, a portion of the warming trend shown in global records derived from the GHCN-adj archive results from the adjustments, not from the underlying data. Our calculations show that this adds about 0.12 degrees to the 20th century average over land.
“The second, and more obvious feature is the chimney-brush appearance of the graph, indicating a massive increase in the volatility of the adjustments after 1990. The instability in the record dwarfs the size of the century-scale global warming signal, with fluctuations routinely going to ±0.5 degrees C from one year to the next. The southern hemisphere (bottom panel) is particularly noisy.
“On substantive grounds I therefore conclude that after 1990 the GHCN archive became very problematic as a basis for computing precise global average temperatures over land and comparing them to earlier decades.”
… and I thought I knew something about the subject …
Clear, detailed, understandable, authoritative, extensive references, code and data provided, very readable, my congratulations to Ross. This one will be a classic.
w.
Let me know when you want to reactivate the GHCN gallery. I’ve got a few stations saved up for you….
jws
This post returns to the theme of the questionable value of areally averaged global temperature in understanding climatic processes. It must always hugely bias the input of temperature oscillation in favour of the tropics at the expense of the high latitudes, since the global area reduces exponentially toward the poles.
The final figure in the following commentary referenced below, credited to George Kukla, demonstrates the bias
http://calderup.wordpress.com/2010/05/14/next-ice-age/
Willis Eschenbach says:
August 3, 2010 at 1:32 am
I think that this is well worth repeating, again and again.
This is indeed, praise of the highest quality.
“On substantive grounds I therefore conclude that after 1990 the GHCN archive became very problematic as a basis for computing precise global average temperatures over land and comparing them to earlier decades.”
This is very much in tune with what E.M. Smith has been saying for a while, most recently yesterday: http://chiefio.wordpress.com/2010/08/02/agw-jumping-sharks-since-1986/
Is it just me, or do the two sudden falls in average latitude c. 1985 and c. 2000 on figure 1.7 correspond rather nicely with the instrumental changes that Chiefio has been blaming for the changing temprature measurements? It looks very like to me that there has been two major relocations/rebalancings of the entire GHCN within the last 30 years, at the same time as instrumental and methodological changes were introduced
Vince Whirlwind, you obviously didn’t download and read the paper which states that the problem is not so much with the variations in post-processing by GISS, HadCRU and NOAA (though it is somewhat) but in the input data itself from GHCN. Foot, mouth, insert.
A great read although I was relieved to find that half the pages were references.
I found the references to the CRU emails were very effective since they showed how corrosive they were in context. The UHI chapter was particularly shocking. How can research without any supporting data be accepted as true whilst research backed by data be dismissed, simply because someone say it is implausible?
So almost all the data from the various climate groups are based on one source. This source has significant biases and uncertainties, similar in magnitude to the purported underlying trend. The science is very doubtful but they get away with it because the police are in the pocket of the criminals – an arrangement that they call peer review!
thank you, Rich Matarese, I was just going to ask. I don’t understand all these abbreviated initial wotsits. I thought it was usual good practice to spell it out first time with the initials in brackets to be used thereafter. Picky, perhaps, but it helps people who are new to this stuff, like me, and it is the ‘proper’ thing to do.
And those deliberate changes culminating in a warming bias just happen to be chance? In politics and in turn, policy, nothing happens by chance; everything is planned and executed to the best of their abilities. The only hiccup is when meddlesome individuals interfere, requiring plans B) C) and so on to be adapted and implemented. This observation will only add to the “to do” list in order for the planned agenda to be realized.
A detailed overview like this is just what was needed. I’d had a go at looking at the adjustments in NOAA/GHCN data back in January*, but had looked at the effect on overall trend. What Ross McKittrick is showing – that the adjustments tend to cool the older records and warm the more recent analysis is something I have seen too but wondered how widespread it was. Now we know.
*Links that look at overall trends:
http://diggingintheclay.wordpress.com/2010/01/21/the-station-drop-out-problem/
http://diggingintheclay.wordpress.com/2010/01/28/adjustment-effects-on-temperature-trends-part-2-magnitudes-of-adjustment/
http://diggingintheclay.wordpress.com/2010/01/29/adjustment-effects-on-temperature-trends-part-3-effects-by-latitude/
It would be interesting to repeat these but segmenting by the periods suggested in the paper.
Paul Clark says:
August 3, 2010 at 3:12 am
“Vince Whirlwind, you obviously didn’t download and read the paper which states that the problem is not so much with the variations in post-processing by GISS, HadCRU and NOAA (though it is somewhat) but in the input data itself from GHCN. Foot, mouth, insert.”
He doesn’t have to read it to make his appeal to authority. He thinks there is some magic trick that only scientists can do when one adds two numbers together and divide by two. Obviously, this paper isn’t the only reading material he’s skipped out of reading.
An excellent paper that should be read by all IPCC sponsored scientists. One thing puzzles me though. On page 11 we see the percentage GHCN stations located at airports from 1890 – 2009. But according to WikiAnswers the first airport was built in 1909, College Park Maryland.
I’ve made a set of KMZ files which you can feed into Google Earth to visualize just what GHCN station changes were made in the 90’s and in 2005.. You can download them as a zipfile; just click on a filename in a file browser or use Ctrl-O in GE, and you will see in GE a set of markers indicating the stations removed, labelled and colored by whether they are urban/rural, sized by years of record, etc. There are other posts with files to show the state of GHCN in each “decade year”.
The post with more description and a download pointer, is here.
Climate science are regional events!
Far too much science is missing to generate an overall Global model.
Are similar bias present between high and low altitude? Rural v city?
Shameless self-promotion: Animation of locations with data Dude, where is my thermometer which visualizes the spatial distribution of locations in the GHCN by year and graphs of station counts by country by year.
So now we see the new iconic image of climate science is not the Hockey Stick – but the Chimney Brush. I look forward to seeing this image on the front page of the next IPCC report.
Thanks to Ross.
Vince Whirlwind at 1:08 AM and Paul Clark at 3:12 AM.
Thank you two for this critical point. This tends to absolve the post processors of chicanery with the data, but how was the change in stations used by GHCN made? And, dare I ask, why?
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Conclusion to be drawn:
There is no systematic requirement for a uniformity of data collection sites in terms of longitude and latitude, land against ocean, low altitude against high altitude.
Ergo: no reliable conclusions about global climate can be drawn.
Proposal: start again with a global consortium, operating openly, scientifically, robustly, skeptically, rigorously, with appropriate redundancy and funded by a partnership of stakeholders to include Administrations, corporations, farmers groups, tourism groups, shipping groups, fishing interests and interested members of the public.
And as the usefulness of this would only be anything other than zero if funding were continuous for at least a century and probably 500 years, it is not something to be undertaken lightly or wastefully………….
This is regarding an area representing 30% of the globe and these records have been known to be corrupt for some time.
The sea surface temperatures are in worse shape and that has also been known for some time but people continue to discuss “Climate” based on known corrupted data.
If someone claims the globe has warmed the response would be: There is no reliable evidence to make that claim!
While this is a good and extensive look at the surface temperature records it should have not been needed. It will be either ignored when possible or trashed by the faithful as not being from an insider. Even though NASA GISS admits that Surface Air Temperature is guess work at best.
Quote:
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.
From here:
http://data.giss.nasa.gov/gistemp/abs_temp.html