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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)

Temperature data is essential for predicting the weather. So, the U.S. National Weather Service, and every other weather service around the world, wants temperatures to be measured as accurately as possible.

To understand climate change we also need to be sure we can trust historical measurements. A group called the International Surface Temperature Initiative is dedicated to making global land temperature data available in a transparent manner.

Surface temperature measurements are collected from about 30,000 stations around the world (Rennie et al. 2014). About 7000 of these have long, consistent monthly records (Fig. 1). 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 some people worried that weather stations placed in poor locations could make the temperature record unreliable. Scientists at the National Climatic Data Center took those critics seriously and did a careful study of the possible problem. Their article "On the reliability of the U.S. surface temperature record" (Menne et al. 2010) had a surprising conclusion. The temperatures from stations that critics claimed were "poorly sited" actually showed slightly cooler maximum daily temperatures compared to the average.  

In 2010 Dr. Richard Muller criticized the "hockey stick" graph and decided to do his own temperature analysis. He organized a group called Berkeley Earth to do an independent study 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)?" Their conclusion was NO. None of those factors bias the temperature record. The Berkeley conclusions about the urban heat effect were nicely explained by Andy Skuce in an SkS post in 2011. Figure 2 shows that the U.S. network does not show differences between rural and urban sites.

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)

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 15 August 2017 by Sarah. View Archives

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Comments 526 to 529 out of 529:

  1. To follow up Eclectic's comment at 525, there are many environmental/geological records that indicate various features of past climates. Vegetation and animal populations are often  linked to local climate, and fossil evidence of past vegetation and animal abundance gives indications of past climates.

    Tree rings go back thousands of years in some cases, and fossil trees can generate longer tree ring records - earlier than the oldest living tree in the area.

    Pollen deposited in lake sediments indicates vegetation at the time the sediment was deposited. In many areas, the lake sediments have annual layers due to summer/winter variations in hydrology, so the layers are easily dated. Thickness of layers gives indications of rainfall/stream flow variations that affect the amount of sediment.

    Eclectic mentioned ice cores, which can give both temperature information and atmospheric gas concentrations (CO2) going back hundreds of thousands of years.

    A search here on "proxy" yields a couple of useful posts:

    Wikipedia has some discussion of the "Hockey Stick"

    Unless your friend knows details of the "reliability" of these many methods of examining past climates, he/she is arguing from a position of lack of knowledge.

  2. Hi Eclectic, yeah, he's not a skeptic he's a denialist, you are right. And thank you for your comment, I'll be sure to pass it on to him.

    I have a follow-up question: how far back can we have reliable temperature measurements ? 100 000 years ? 800 000 years?

    Best regards

  3. Wongfeihung1984:

    Every method of calculating (from direct measurements of local temperatures) or estimating (via proxy, satellite, etc) global temperatures has uncertainties. "Reliable" is a subjective term, and is not very useful.

    Each original source of a global temperature time series will have some sort of indication of uncertainty. You really need to pick a particular method, find the original source, and see what it says. Generally, uncertainty will increase as you go back in time, and as you move towards more local temperatures from fewer data sources.

    The Tai-Chi link in my comment #526 includes this graphic, as an example, showing one standard deviation in the uncertainty:

    Temperature proxies

  4. Wongfeihung1984 @527,
    Proxy data of varying usefulness allows a global temperature record with reducing detail back 500 million years.

    500My temperature record


    Widely known, the ice core data go back 100ky in the Arctic & 800k in the Antarctic while similar isotope dating methods in ocean sediments provide data back to, for instance in the graph above, the 65My of Zachos et al (2001), or the 5.3My of Lisiecki & Raymo (2005) which for most purposes can be converted into a global temperature record.
    While generally 'reliable', such data-use is considered less than 'reliable' for some purposes so perhaps the 2,000ky record of Snyder (2016) which uses multiple proxies is likely the longest that could be properly termed 'reliable'.

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