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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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Are surface temperature records reliable?

What the science says...

Select a level... Basic Intermediate Advanced

The warming trend is the same in rural and urban areas, measured by thermometers and satellites, and by natural thermometers.

Climate Myth...

Temp record is unreliable

"We found [U.S. weather] stations located next to the exhaust fans of air conditioning units, surrounded by asphalt parking lots and roads, on blistering-hot rooftops, and near sidewalks and buildings that absorb and radiate heat. We found 68 stations located at wastewater treatment plants, where the process of waste digestion causes temperatures to be higher than in surrounding areas.

In fact, we found that 89 percent of the stations – nearly 9 of every 10 – fail to meet the National Weather Service’s own siting requirements that stations must be 30 meters (about 100 feet) or more away from an artificial heating or radiating/reflecting heat source." (Watts 2009)

At a glance

It's important to understand one thing above all: the vast majority of climate change denialism does not occur in the world of science, but on the internet. Specifically in the blog-world: anyone can blog or have a social media account and say whatever they want to say. And they do. We all saw plenty of that during the Covid-19 pandemic, seemingly offering an open invitation to step up and proclaim, "I know better than all those scientists!"

A few years ago in the USA, an online project was launched with its participants taking photos of some American weather stations. The idea behind it was to draw attention to stations thought to be badly-sited for the purpose of recording temperature. The logic behind this, they thought, was that if temperature records from a number of U.S. sites could be discredited, then global warming could be declared a hoax. Never mind that the U.S. is a relatively small portion of the Earth;s surface. And what about all the other indicators pointing firmly at warming? Huge reductions in sea ice, poleward migrations of many species, retreating glaciers, rising seas - that sort of thing. None of these things apparently mattered if part of the picture could be shown to be flawed.

But they forgot one thing. Professional climate scientists already knew a great deal about things that can cause outliers in temperature datasets. One example will suffice. When compiling temperature records, NASA's Goddard Institute for Space Studies goes to great pains to remove any possible influence from things like the urban heat island effect. That effect describes the fact that densely built-up parts of cities are likely to be a bit warmer due to all of that human activity.

How they do this is to take the urban temperature trends and compare them to the rural trends of the surrounding countryside. They then adjust the urban trend so it matches the rural trend – thereby removing that urban effect. This is not 'tampering' with data: it's a tried and tested method of removing local outliers from regional trends to get more realistic results.

As this methodology was being developed, some findings were surprising at first glance. Often, excess urban warming was small in amount. Even more surprisingly, a significant number of urban trends were cooler relative to their country surroundings. But that's because weather stations are often sited in relatively cool areas within a city, such as parks.

Finally, there have been independent analyses of global temperature datasets that had very similar results to NASA. 'Berkeley Earth Surface Temperatures' study (BEST) is a well-known example and was carried out at the University of California, starting in 2010. The physicist who initiated that study was formerly a climate change skeptic. Not so much now!

Please use this form to provide feedback about this new "At a glance" section, which was updated on May 27, 2023 to improve its readability. Read a more technical version below or dig deeper via the tabs above!

Further details

Temperature data are essential for predicting the weather and recording climate trends. So organisations like the U.S. National Weather Service, and indeed every national weather service around the world, require temperatures to be measured as accurately as possible. To understand climate change we also need to be sure we can trust historical measurements.

Surface temperature measurements are collected from more than 30,000 stations around the world (Rennie et al. 2014). About 7000 of these have long, consistent monthly records. As technology gets better, stations are updated with newer equipment. When equipment is updated or stations are moved, the new data is compared to the old record to be sure measurements are consistent over time.

 GHCN-M stations

Figure 1. Station locations with at least 1 month of data in the monthly Global Historical Climatology Network (GHCN-M). This set of 7280 stations are used in the global land surface databank. (Rennie et al. 2014)

In 2009 allegations were made in the blogosphere that weather stations placed in what some thought to be 'poor' locations could make the temperature record unreliable (and therefore, in certain minds, global warming would be shown to be a flawed concept). Scientists at the National Climatic Data Center took those allegations very seriously. They undertook a careful study of the possible problem and published the results in 2010. The paper, "On the reliability of the U.S. surface temperature record" (Menne et al. 2010), had an interesting conclusion. The temperatures from stations that the self-appointed critics claimed were "poorly sited" actually showed slightly cooler maximum daily temperatures compared to the average.

Around the same time, a physicist who was originally hostile to the concept of anthropogenic global warming, Dr. Richard Muller, decided to do his own temperature analysis. This proposal was loudly cheered in certain sections of the blogosphere where it was assumed the work would, wait for it, disprove global warming.

To undertake the work, Muller organized a group called Berkeley Earth to do an independent study (Berkeley Earth Surface Temperature study or BEST) of the temperature record. They specifically wanted  to answer the question, “is the temperature rise on land improperly affected by the four key biases (station quality, homogenization, urban heat island, and station selection)?" The BEST project had the goal of merging all of the world’s temperature data sets into a common data set. It was a huge challenge.

Their eventual conclusions, after much hard analytical toil, were as follows:

1) The accuracy of the land surface temperature record was confirmed;

2) The BEST study used more data than previous studies but came to essentially the same conclusion;

3) The influence of the urban stations on the global record is very small and, if present at all, is biased on the cool side.

Muller commented: “I was not expecting this, but as a scientist, I feel it is my duty to let the evidence change my mind.” On that, certain parts of the blogosphere went into a state of meltdown. The lesson to be learned from such goings on is, “be careful what you wish for”. Presuming that improving temperature records will remove or significantly lower the global warming signal is not the wisest of things to do.

The BEST conclusions about the urban heat effect were nicely explained by our late colleague, Andy Skuce, in a post here at Skeptical Science in 2011. Figure 2 shows BEST plotted against several other major global temperature datasets. There may be some disagreement between individual datasets, especially towards the start of the record in the 19th Century, but the trends are all unequivocally the same.

rural-urban T

Figure 2. Comparison of spatially gridded minimum temperatures for U.S. Historical Climatology Network (USHCN) data adjusted for time-of-day (TOB) only, and selected for rural or urban neighborhoods after homogenization to remove biases. (Hausfather et al. 2013)

Finally, temperatures measured on land are only one part of understanding the climate. We track many indicators of climate change to get the big picture. All indicators point to the same conclusion: the global temperature is increasing.


See also

Understanding adjustments to temperature dataZeke Hausfather

Explainer: How data adjustments affect global temperature recordsZeke Hausfather

Time-of-observation Bias, John Hartz

Berkeley Earth Surface Temperature Study: “The effect of urban heating on the global trends is nearly negligible,” Andy Skuce

Check original data

All the Berkeley Earth data and analyses are available online at

Plot your own temperature trends with Kevin's calculator.

Or plot the differences with rural, urban, or selected regions with another calculator by Kevin

NASA GISS Surface Temperature Analysis (GISSTEMP) describes how NASA handles the urban heat effect and links to current data.

NOAA Global Historical Climate Network (GHCN) DailyGHCN-Daily contains records from over 100,000 stations in 180 countries and territories.

Last updated on 27 May 2023 by John Mason. View Archives

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Further reading

Denial101x video

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial

Additional video from the MOOC

Kevin Cowtan: Heat in the city


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Comments 126 to 150 out of 521:

  1. Using only station records when there are two versions of satellite data available is a form of cherry picking. Since those are limited time wise, I propose that a compromise set be used. This is the set I will use from now on for the instrumental period. It is a merged set that uses the CRU, Hadley, UAH and RSS. Details are available on my site as well as the file. No set is perfect, but I hope that using a set like this is acceptable, more reliable and reduces the complaints from each side of the debate on which set of data they use.…rement-is-best/ John Kehr The Inconvenient Skeptic
  2. John Kehr - you do realise that they dont measure the same thing? (and your link doesnt work). Satellite data lower troposphere is temps through section of atmosphere at around 4000m. Try reading up on how MSU measurements are made, corrected etc. ALL of them valuable, all of them show a warming trend. I think your method of combination is bogus - you need to find a way to reflect the way lower troposphere temperature operates with surface temperature.
  3. Doh!!... Those darn links... Working link. I did indicate that the satellite measurement is a measurement of wavelength. I am not saying that it is perfect method, but none of them are perfect. Hadley and CRU also give different results. This is the one place where anomaly is beneficial. I think it is a more useful method than all skeptics using satellite only and the AGW crowd using CRU only. Instead of arguing about interpolation methods and UHI I am using more sources of anomaly data. If you have a better proposal for incorporating satellite data into a standard record I am all ears. I don't particularly care what method is used, but a single set that attempts to use the station and satellite data would be helpful for all.
  4. Well me, if I wanted to know what is going on in the surface record, I would use the surface temperature record. If I wanted to know what is going on in lower troposphere, I would use MSU data. Giving the complexities in the relationship, I would certainly not be interested in a combination, least of all one put together with arbitrary weightings. What would you think of someone doing this in your area? Think you could get such an approach published. I did indicate how you would combine them properly but first you solve a very difficult problem. Also, the idea that "skeptics" use satellite and AGW use surface is bogus. It is use for what purpose.
  5. Re: The Inconvenient Skeptic As scaddenp rightly points out, you are in error. The atmosphere is layered, like an onion. The different dataset sources measure different things. Attempting to homogenize them into a "blended" dataset is less like comparing apples to oranges than it is comparing apples and breadfruit. Attempting to shift the focus of the debate to "skeptics using satellite only and the AGW crowd using CRU only" is also misleading. Scientist use the theory that best explains the preponderance of the data. Multiple, independent lines of evidence (of which station data and satellite data are but two) show that our world is warming and that we are causing it. That is what science is telling us. Most "skeptics" choose to focus on part of the evidence available rather than all of it. I can appreciate wanting to roll all of the instrumental data (station and satellite) into one neat package, but it isn't necessary. It's rather like combining the four Gospels into one continuous narrative: while interesting, it doesn't tell us anything we don't already know. The Yooper
  6. TIS writes: I think it is a more useful method than all skeptics using satellite only and the AGW crowd using CRU only. I don't know where you get that impression. I tend to use the satellite record if I'm making a point about recent years, and the instrumental record if the topic is longer term. You can find nice examples of comments where I used the satellite temperature record here and here. Note also that if you click on the "Advanced" tab at the top of this page, then scan down to figure 7, you'll see a comparison of temperature reconstructions in which I averaged the various instrumental records to get a "surface" record, and averaged the satellite records to get a "lower troposphere" record.
  7. ice-core samples are WORTHLESS EVIDENCE, as proven at . And since this Global Warming has only this physical evidence (witll all else being ambiguous), then their argument FAILS.
    Response: Please be sure to review the Comments Policy before posting. In particular, we ask that you refrain from posting duplicate comments in multiple threads, and avoid the use of ALL CAPS.
  8. KirkSkywalker - Your referenced web page is mistaken. CO2 is not retained as dry ice in ice cores, but rather as gas bubbles (little icy air tanks). Since that's the only argument presented on the page, I find it lacking content. To include the quote from that page: “A single fact will often spoil a most interesting argument.” –William Feather
  9. KirkSkywalker - Thinking back, I recalled something like this before. Googling a bit, I found that you had posted the same error about ice cores here, on Oct. 23. And had received the same reply from me. Are you reading this website (the point of a discussion is to, in fact, discuss), or just posting and walking away?
    Response: KR, thank you for your vigilance in noting that the same point is being raised in multiple threads. The thread where you responded to KirkSkywalker's comment last month (What does past climate change tell us about global warming?) is probably a better fit than this one for discussion of ice cores. Let's have any further discussion of KirkSkywalker's claims about ice cores take place over there.
  10. Kirk: "And since this Global Warming has only this physical evidence (witll all else being ambiguous), then their argument FAILS." Kirk, if you want physical evidence for global warming, go here and also here and here. You might also truck on over to here if you want to get a grip on the physics of GW.
  11. Hi all, I've been hearing a lot about degraded NOAA satellites. Most of what I find on it is from viciously slanted blogs This MSU webpage was pointed out to me. It confirms some degree of difficulties with one or more NOAA satellites that resulted in some distorted thermal images. I'm having trouble finding information on the temporal duration of the issues. I also don't know what data has been affected. Does anyone have an answer to this challenge? Thanks.
    Response: [Daniel Bailey] This was addressed by Ned at Great-Lakes-satellite-temperature.
  12. Thanks Yooper, Hey I was at the University of Michigan Biological Station this June and July, and I toured the Upper Peninsula a bit. Do you do research in Michigan?
  13. Re: Rovinpiper (137) Sorry, I no longer work in the Earth Sciences fields. In pharmaceuticals now, living where I want to live instead of doing the work I wanted to do & hating where I was living (Washington, DC). If you want to chat via email, send it to John Cook here at Skeptical Science & he'll forward it to me. The Yooper
  14. Here is the link to "Tales from the thermometer" which is available via replay wayback machine: Which brings up my question on the temp data sets, the HadCRU and GISS ones are the same thermometers, with different data adjusting procedures etc..., while the GSOD database has many more stations - my question is does it also include the GHCN stations (while adding many more), or is it a set of completely distinct stations? I couldn't find for sure from the links at Ned #90...Also, are there any other worldwide surface station data sets distinct from the GHCN that have been looked at? Many thanks!!
  15. If anyone cares I emailed the folks who have done the GSOD database, and it sounds like the GHCN daily record has an overlap with 4131 GSOD stations, but that the GHCN monthly stations(which according to the above provide the 3 main temperature datasets) do not overlap with the GSOD stations. Still not quite sure I understand that so if anyone has any other info feel free to chime in!
  16. I am looking for information on how NASA GISS fills in the gaps on the Arctic temperature grids. I just want a better understanding. Thanks.
  17. RickG, have a look at GLOBAL SURFACE TEMPERATURE CHANGE, J. Hansen, R. Ruedy, M. Sato, and K. Lo
  18. GISS Temp is the obvious place to start where the papers referencing the methodology method are given. You might like to look at Ned's post above #102 to help you guess whether the hadcrut method (use global average to interpolate) or GISS method (infer for local station analysis) might give best answer for Arctic.
  19. Responding cloa513 from here If someone was averaging temperatures in the way you seem to think they are, then you would have a point. However, if you see Hansen 2008, the keepers of temperature record would agree and so that is NOT how it is done. It has been pointed out to you before with the links to the actual method, so why are you persisting with this erroneous strawman?
  20. Reply to comment from here. "The Berkeley Earth Surface Temperature project is incorporating criticism of data collection sites" And here is what the BEST project says as of today: We are first analyzing a small subset of data (2%) to check our programs and statistical methods and make sure that they are functioning effectively. We are correcting our programs and methods while still “blind” to the results so that there is less chance of inadvertently introducing a bias. The Berkeley Earth team feels very strongly that no conclusions can yet be drawn from this preliminary analysis. -- emphasis added Best to wait until there's a finding before rushing to judgment. But then, you're reading Watt$.
  21. At NASA's GISS Surface Temperature Analysis webpage The Annual Mean Temperature Change in the United States appears to have peaked and is dropping at the end of the graph?
  22. 146 sjshaker Ask you self this. If you had seen that graph in the early 1990s - obviously only with the numbers up to then - would you not say the same thing? Would you have been right? Given which, do you think looking at the ups and downs over a time range of a couple of years is reliable?
  23. Keep in mind, Chris, that Fig D you refer to is only for the United States and is based on running 5-year means. In English, this translates to the info shown for the last 5 years on the graph is less certain and more variable (relative to that which preceded it). The Yooper
  24. Gee, Chris, noticed that it has dropped before? I can think I can predict with some confidence that this year will be cooler than last year. Why? La Nina. I can also bet with reasonable confidence it will be warmer than the last La nina of similar magnitude. And guess what, temperatures will go up again in the next EL Nino. Do you become a climate skeptic in La Nina years, and warmist in El Nino?
  25. I've been looking for long term historical data from climate records for specific met sites that I can download and graph on my own. So far, Google has not provided. I did find and read some nice Wikipedia entries on Climate records, controversies about same, and more about the Berkeley Earth Surface Temperature Project Also found access to "Uncertainty estimates in regional and global observed temperature changes: a new dataset from 1850" I would appreciate pointers to raw data that we can download ourselves. Chris Shaker
    Response: Go to Click the Data Sources link in the horizontal bar at the top of that page.

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