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Assessing global surface temperature reconstructions

Posted on 24 July 2010 by Ned

Guest post by Ned

There are three prominent reconstructions of monthly global mean surface temperature (GMST) from instrumental data (fig. 1):  NASA's GISTEMP analysis, the CRUTEM analysis (from the University of East Anglia's Climatic Research Unit), and an analysis by NOAA's National Climatic Data Center (NCDC).  

Figure 1.  Comparison of global (land & ocean) mean surface temperature reconstructions from NASA GISS, the University of East Anglia's CRU, and NOAA NCDC.

How reliable are these temperature reconstructions? Various questions have been raised about both the data and the methods used to produce them.  Now, thanks to the hard work of many people, we can conclude that the three global temperature analyses are reasonable, and the true surface temperature trend is unlikely to be substantially different from the picture drawn by NASA, CRU, and NOAA.

The three GMST analyses have much in common, though there are significant differences among them as well.  All three have at their core the monthly temperature data from the Global Historical Climatology Network (GHCN), and all three produce both a land-stations-only reconstruction and a combined land/ocean reconstruction that includes sea surface temperature measurements.

Let's explore the reliability of these reconstructions, from several different angles.

The data and software used to produce these reconstructions are publicly available

Source code and data to recreate GISTEMP and CRUTEM are available from NASA and CRU websites.  (The data set provided by CRU excludes a fraction of the data that were obtained from third parties, but the results are not substantially affected by this).

The software has been successfully tested outside of NASA and CRU, and it works as advertised

Both GISTEMP and CRUTEM have been successfully implemented by independent investigators. For example, Ron Broberg has run both the CRUTEM and GISTEMP code.  In addition, the Clear Climate Code project has duplicated GISTEMP in Python.   Figure 2 shows a comparison of the output of the GISTEMP reconstruction process as implemented by NASA and by Clear Climate Code ... but since the results are identical, the second line falls exactly on top of the first.

Comparison of GISTEMP and CCC

Figure 2.  The GISTEMP land/ocean temperature analysis as implemented by NASA and by Clear Climate Code.   Results of the two analyses are effectively identical.

Similar results can be obtained using different software and methods

Over the past year, there has been quite a flurry of "do-it-yourself" temperature reconstructions by independent analysts, using either land-only or combined land-ocean data.  In addition to the previously-mentioned work by Ron Broberg and Clear Climate Code, these include the following:

(There are probably others as well that we're omitting!)

Most recently, the Muir Russell investigation in the UK was able to write their own software for global temperature analysis in a couple of days.

For all of these cases, the results are generally quite close to the "official" results from NASA GISS, CRU, and NOAA NCDC. Figure 3 shows a collection of seven land-only reconstructions, and Figure 4 shows five global (land-ocean) reconstructions.


Figure 3.  Comparison of land-only reconstructions, 1900-2009.  Note that the NASA GISS reconstruction using only land stations is not shown here, because it is conceptually different from the other analyses.

Figure 4.  Comparison of land-ocean reconstructions, 1900-2009.

Obviously, the results of the reconstructions are quite similar, whether they're by the "Big Three" or by independent analysts.


The temperature increase is not an artifact of the GHCN adjustment process

Most of the analyses shown above actually use the raw (unadjusted) GHCN data.  Zeke Hausfather has done comparisons using both the adjusted and raw versions of the GHCN data set, and as shown in fig. 5, the results are not substantially different at the global scale (though 2008 is a bit of an outlier).

Figure 5.  Comparison of global temperatures from raw and adjusted GHCN data, 1900-2009 (analysis by Zeke Hausfather).


The temperature increase is not an artifact of declining numbers of stations

While it is true that the number of stations in GHCN has decreased since the early 1990s, that has no real effect on the results of spatially weighted global temperature reconstructions.  How do we know this?

* Comparisons of trends for stations that dropped out versus stations that persisted post-1990 show no difference in the two populations prior to the dropouts (see, e.g., here and here and here).

* The spatial weighting processes (e.g., gridding) used in these analyses makes them robust to the loss of stations.  In fact, Nick Stokes has shown that it's possible to derive a global temperature reconstruction using just 61 stations worldwide (in this case, all the stations from GISTEMP that are classified as rural, have at least 90 years of data, and have data in 2010).

* Other data sets that don't suffer from GHCN's decline in station numbers show the same temperature increase (see below).

 One prominent claim (by Joe D'Aleo and Anthony Watts) was that the loss of "cool" stations (at high altitudes, high latitudes, and rural areas) created a warming bias in the temperature trends.  But Ron Broberg conclusively disproved this, by comparing trends after removing the categories of stations in question.  D'Aleo and Watts are simply wrong.


The temperature increase is not an artifact of stations being located at airports

This might seem like an odd statement, but some people have suggested that the tendency for weather stations to be located at airports has artificially inflated the temperature trend.  Fortunately, there is not much difference in the temperature trend between airport and non-airport stations.


The temperature increase is present in other data sets, not just GHCN

All of the above studies rely (mostly or entirely) on monthly station data from the GHCN database.  But it turns out that other, independent data sets give very similar results.


Figure 6.  Comparison of global temperatures from the Global Historical Climatology Network (GHCN) and Global Summary of the Day (GSOD) databases. (Analysis by Ron Broberg and Nick Stokes).

What about satellite measurements of temperatures in the lower troposphere?  There are two widely cited analyses of temperature trends from the MSU sensor on NOAA's polar orbiting earth observation satellites, one from Remote Sensing Systems (RSS) and one from the University of Alabama-Huntsville (UAH).  These data only go back to 1979, but they do provide a good comparison to the surface temperature data over the past three decades.  Figure 7 shows a comparison of land, ocean, and global temperature data from the surface reconstructions (averaging the multiple analyses shown in figs. 3 and 4) and from satellites (averaging the results from RSS and UAH):


Figure 7.  Comparison of temperatures from surface stations and satellite monitoring of the lower troposphere.

We'll end by looking at all the surface and satellite-based temperature trends over the entire period for which both are available (1979-present).  What are the trends in the various data sets and regions?  As shown in fig. 8, the surface temperature trends over land have a fair amount of variability, but all lie between +0.2 and +0.3 C/decade.  Surface trends that include the oceans are more uniform. 

Figure 8.  Comparison of temperature trends, in degrees C per decade.

Overall, the satellite measurements show lower trends than surface measurements.   This is a bit of a puzzle, because climate models suggest that overall the lower troposphere should be warming about 1.2X faster than the surface (though over land there should be little difference, or the surface should be warming faster).  Thus, there are at least three possibilities:  

  • The surface temperature trends show slightly too much warming.
  • The satellite temperature trends show slightly too little warming.
  • The prediction of climate models (about amplified warming in the lower troposphere) is incorrect, or there are complicating factors that are being missed. 

It should be noted that in the past the discrepancy between surface and satellite temperature trends was much larger.  Correcting various errors in the processing of the satellite data has brought them into much closer agreement with the surface data. 


The well-known and widely-cited reconstructions of global temperature, produced by NASA GISS, UEA CRU, and NOAA NCDC, are replicable

Independent studies using different software, different methods, and different data sets yield very similar results.  

The increase in temperatures since 1975 is a consistent feature of all reconstructions.  This increase cannot be explained as an artifact of the adjustment process, the decrease in station numbers, or other non-climatological factors. 

In contrast to normal practice here at Skeptical Science, for this post we have emphasized the "near-real-time" results of studies undertaken by individuals (in some cases non-specialists and highly talented amateurs) as published on blogs, rather than the work of professional scientists published in the peer reviewed literature. Since many of the "controversies" about the reliability of surface temperature trends first arose in the blogosphere, it is perhaps appropriate that those controversies are now being carefully and thoughtfully resolved in the same environment.



We would like to thank the scientists of GISS, CRU, and NCDC for their work and their patience.  We would also like to thank the individual authors of the "independent" temperature analyses featured here, particularly Zeke Hausfather who compiled the results of multiple different reconstructions, and Lucia L. who provides space for Zeke's work on her blog.

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Comments 51 to 73 out of 73:

  1. Ned, I'm a bit late to stumble upon this, but great summary of the work to date. One quick clarification: figure 5 is based on an incorrect interpretation of the v2.mean_adj dataset. Namely, it is a change-log rather than an independent dataset in its own right, and should be combined with all v2.mean months not present in v2.mean_adj. When that is done, the differences become much smaller. See the update on the bottom of The net adjustments can be seen here:
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  2. Hi, Zeke. Thanks for stopping by, for the kind words, and for the correction to figure 5. The two time-series are already quite similar, so if this brings them even closer together the results must be virtually indistinguishable! In any case, I'll update the post to reflect this (though it may be a couple of days before I'm able to do so). I'm sure you're a busy guy, and seems to be a good venue for your writings. But if and when you have the time, we'd all very much appreciate any thoughts you'd care to share over here.
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  3. Hi, I'm a student doing a Cambridge Pre-U essay and I need to find out the names of some of the scientists who have found that temperatures have risen by "over 0.5 degrees Celcius in under 100 years" and I also need to find the names of some prominent scepticswho have pointed out the Medieval Warm Period as evidence of a continual natural cycle of warming and cooling. If anyone could help me find some names of such scientists/sceptics it would be much appreciated, Thanks
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  4. Are there any peer reviewed article there that gives deterministic answer for "How global surface temperature is reconstructed with each worldly known contributory factors and its corresponding weights? In short, I am only looking for temperature defining budget balance statement template, that can be used over the years to clearly test with observed data. Additionally one can also give temperature-flow statement, similar like we have cash-flow statements in accounting and auditing professions. Please only provide pin-point reference matching the need expressed, else refrain responding.
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  5. patonomics - "Are there any peer reviewed article there that gives deterministic answer for "How global surface temperature is reconstructed with each worldly known contributory factors and its corresponding weights?"" What you appear to be looking for are attribution studies. I would suggest you read the Comprehensive Review of the Causes of Global Warming, as the papers listed there are exactly what you are asking for. You can use those as references regarding forecasting and hindcasting temperatures. In addition you might benefit from looking at Trenberth et al 2009, Earth's global energy budget, which discusses energy flows. "Please only provide pin-point reference matching the need expressed, else refrain responding." - Please avoid the inflammatory tone, lest you simply get ignored.
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  6. #54 patonomics, in addition to KR's links, if you really want to know how global surface temperature records are constructed, you would do worse than to look at Glenn Tamblyn's 4-part series "On Averages and Anomalies" here at SkS (first post linked). They are an excellent complement to the above post, and will tell you a great deal about how we determine the surface temperature record. And remember, readers here are free to respond to any post they like, so long as they conform with the Comments Policy!
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  7. patonomics#54: You asked a virtually identical question on this thread and rejected all replies. Then you stated you couldn't be bothered to do the research. So what is different this time? Consider looking at the fundamental paper by Meehl et al 2004, if it is not too much bother. The late-twentieth-century warming can only be reproduced in the model with anthropogenic forcing (mainly GHGs), while the early twentieth-century warming is mainly caused by natural forcing in the model (mainly solar). However, the signature of globally averaged temperature at any time in the twentieth century is a direct consequence of the sum of the forcings. There follows considerable discussion of principal component analysis. And please do not presume to instruct others whether they can respond to your requests.
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  8. It's all there but we have to package it nicely for you eh? Radiative transfer laws, fluid dynamics, atmospheric chemistry etc, etc. Patonomics's thought process and sequence of actions is unfortunately all too common. It usually proceeds like this: One comes on this site touting very entrenched ideas on the nature of scientific knowledge and/or the scientific process, all of these ideas being somewhat supeficial, wrong, oversimplified or misguided. From there, one proceeds on to claim that climate science findings are moot unless such or such demand is met. However, when more specific concerns are adressed, the poster reveals that he/she has not done the ground work, but then states he wants others to do it for him. I am not about to do that work, I have enough of my own. In my several years of reading and contributing to SkS, I have seen this, and worse things, happen more times than I can count. If Patonomics considers himself to have the intellectual honesty needed, then he must do his own research. Starting with Spencer Weart, going to Meehl, Trenberth, Iacono and Clough, etc, etc. Last thing Patonomics: You have no authority to dictate reactions to your posts. If this one does please you, move on. I did not write it specifically for you but for any reader who would happen to have an interest in this thread.
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  9. muoncounter#57: "Consider looking at the fundamental paper by Meehl et al 2004, if it is not too much bother." Thank you very much. "3) GHG (CO2, water vapor, O3, CH4, N2O, CFC12, CFC11) (G)" I am really looking for, each component breakdown of GHG and then for each GHG component, further breakdown for 1) 'by source' and 2) 'by sink' for those sub-component and there respective weights. If you know some peer reviewed document, you may through some light.
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    [DB] "If you know some peer reviewed document, you may through some light."

    Fiat Lux.  Try the IPCC AR4, found on this page:

    A very accessible and useful search tool for it can be found here:

  10. Philippe Chantreau#58: "It's all there but we have to package it nicely for you eh?" - Not at all. I am asking to the guys who might claim the knowledge is definite/deterministic in AGW, then don't you think that "any 'man in the street' expecting that packaging is done already". Is that expectation is too much to ask, or its obvious expectation?
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  11. @patonomics. Trolling!!! Really, you profess to ask for knowledge, but you ask for "definite", "deterministic", "breakdown by source/sink". Either you do not understand how science of the big works or you are doing that on purpose, ergo Trolling!!. There are no deterministic/precise/exact answers. Only observations, attributions, trends, cause and effect relationships. The same way that you were asking for a simple equation!! There is no simple answer. We know all the components, we understand most of the physics,and we realize the connectivity between the various physical phenomena in models to test if the connectivity is accurate to give us further understanding. The only true quantitative solution of the fully coupled physics is nature itself. Back to sink/sources and respective weights??? We know them as well as we know GDP.
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  12. I reluctantly must agree with DrTsk here on patonomics (not because of anything with DrTsk, as the good doctor always has pertinent insights to share). Patonomics is simply trolling with the straw man arguements & goalpost shifting. Science is difficult, at best, to understand. And as (essentially) a multidisciplinary and interdisciplinary field, climate science is even more so difficult. Proof that he has some understanding of this is found on his own website, which I will not link here. Patonomics therefore sets up an artificial barrier to understanding by the conditions he imposes. There simply is no substitute for doing the hard work needed to gain the level of comprehension he asks. And to then further limit possible answers to predetermined formats is also trolling. Do the work. Or accept the answers already locatable at many websites, not just this one. Else you are here simply to waste time. Ours and yours.
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  13. DrTsk#61 "The only true quantitative solution of the fully coupled physics is nature itself." - I could not agree with more. why then so much noise around AGW? What it helps one "to claim as science" in their respective profession?
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  14. Huh??? How did you manage to make the connection between what I said and "why then so much noise around AGW?". Ehhh, sorry for a microsecond I thought you are honest and not trolling. We are the forcing!! We understand that, even if we cannot 100% quantify it. Sorry but the insurance industry works with infinitesimal percentages. You don't go back and ask them where is their 100% certainty before you pay your bills!! It is a good insurance to reduce our GHG emissions. Sorry but there is no GEICO for nature. Nobody will replace it if we total it!!
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  15. DrTsk#64: "It is a good insurance to reduce our GHG emissions." - I support that though process completely. (-snipMy only concern (with professionals who claim "AGW is science", and nothing else) that support with your statement "There are no deterministic/precise/exact answers." at DrTsk#61,-)
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    [DB] Off-topic snipped.

  16. patonomics wrote: "why then so much noise around AGW?" Because... nature is demonstrating the impacts of AGW. Duh? Or hadn't you noticed the decreasing global ice coverage, species migrations, seasonal shifts, atmospheric circulation changes, weather changes, rising temperatures, ocean acidification, et cetera? To look at nature and not see AGW one needs to be willfully blind.
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  17. @"AGW is no science". Could not be more wrong. AGW is basic physics, as basic as you can get. You either have no clue what science is or you are trolling. By the way. Chaos is deterministic. Not random. That does not mean you can model a chaotic system 100%.
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  18. Patonomics, you are demonstrating exactly what I argued. If you were sincere, you would already have found on your own all the info linked by moderator above. Language seems to be a barrier but I get your drift with your "man on the street argument." I'm sure the man on the street expects this "packaging" no more than he would with oncology. Do I hear anyone demanding determinism with cancer treatment? [crickets chirping]. No, I guess something that works will suffice after all. Of course, in these matters too the answers will be unwelcome and subjected to all sorts of denial, as with the tobacco wars. It is becoming more and more obvious that you are no interested in learning about reality. If you were, you'd already know better. I'd recommend all: DNFTT.
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  19. Philippe Chantreau#68: (-snip"Do I hear anyone demanding determinism with cancer treatment?" - - - -I have lost my mother in 1985 by NOT asking the deterministic question to the top (Provincial head, country head and many more) surgeons/Medicine Dr , just by putting him on high pedestal. And they ALL show extremely confidence all will be fine, till 3 years after 3 brain surgery and tons of medication (later declared by mail, by one doctor that quantity was enough to poison someone to death, so he will like not see my mother, she will die anyway) when they had no clue what hell they are claiming. Only when the sign of her death is imminent and all their hunch (earlier confidently claimed they know for sure)treatment was all proven wrong one after another, I understood man in the street is losing, if NOT asking the right question to the specialist.-) (-snipIn 2004 however I had the courage to ask the right question head on to the specialist when my father fell ill, and told his chose any of the following 3 options, and I will respect you - - - 1) I know for sure about the problem and how to solve, 2) I do not know how to cure 3) I know for sure no body knows any better than me, all though I am not sure. This time I told top doctor I could find in the country, and I told him I am layman in medical science, but unless his diagnosis is 100% he is suppose NOT to push any injection/medicine. Fortunately this time I get my father back fairly soon within a month to path of recovery, although after a long waiting to do all diagnosis needed to be 100% sure, and then with correct yet complex surgery.-) DrTsk#64: (-snip"We are the forcing!! We understand that, even if we cannot 100% quantify it. Sorry but the insurance industry works with infinitesimal percentages. You don't go back and ask them where is their 100% certainty before you pay your bills!!" - - - - - Insurance is a free choice of man to take or not to take, to believe or not to believe, asking risk justification or not. But try forcing Insurance to all humankind - sure some will demand deterministic answer. I am just one individual, who happen to ask my question to specialists.-) (-snipLabeling someone as troll is easy, I could have done the same, but that's my nature!-)
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    [DB] The topic of this post is Assessing global surface temperature reconstructions, not health care.  While sensitive to the nature of the information you share, it has no bearing on the topic of this post.

    Everyone, please refrain from anything that patonomics may construe as baiting.

    Patonomics, if you genuinely wish to learn more about climate science, this website is a great resource, if approached with the right attitude and without ideological preconceptions.  If it is not a good fit for you, there are other highly recommended websites that you could be referred to.

    Off-topic snipped.

  20. Patonomics: You have still not taken the advice you have been given to read the background. Until you have some basic knowledge you cannot add anything to the conversation. Climate Change is a complex subject. You are responsible for finding out the background from the material that has been referred to you and raising the level of your knowledge. If you cannot reference peer reviewed papers to support your wild claims you need to read more. You have been provided with a great amount of data. Please go read it so you can contribute something.
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  21. Micheal Sweet - Patonomics is playing the "impossible expectations" card. With his impossible expectations unable to be met by any scientific discipline, he can convince himself of whatever he chooses. Hard to say whether this just a more polite, sophisticated form of trolling, or if he really does believe what he writes. But regardless, I fear any advice to him will fall upon deaf ears.
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  22. DB, I must say that it was not my intention to bait on an off-topic subject. The impossible expectation of pure deterministic knowledge is in fact not widespread among people, this was the first example that came to my mind as an illustration, but there are plenty of others (geology comes to mind).
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  23. Philippe, my words (not singling anyone out) were
    "Everyone, please refrain from anything that patonomics may construe as baiting."
    with the operative word being "construe". Given the circumstances, patonomics is protecting his "secret inner worldview" by selectively ignoring, misinterpreting, taking out of context and by even deliberately taking faux outrage at perceived slights from among the best-intended contributions of others. Given such an individual, "blind" by his own volition, perhaps the best response is no response at all. It is not my wont to tell stories, but in this case I shall make exception:
    There once was a US politician from the southern part of the country. This gentleman had won elections so often his victories could not easily be counted. At a political rally, a shy boy came up to the great man and asked "Sir, what is the secret to your being able to win so many elections?" The politician smiled, knelt and whispered into the boy's ear (so no one else could hear), "Son, the secret to winning an election is to keep the third of the people who hate your guts from swaying the third of the people who have yet to make up their minds..."
    The obvious takeaway being that there exist those whom you trust, those in the middle and those that you cannot trust. Some lost sheep are unrepentant and unrecoverable. For those last, shake the dust off of your feet and move on. Let us go and do likewise.
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