Who counts the temperature
The next article (here) looks critically at how the global average temperature figure is assembled but we do need first to just note who does this actual assembling. Its often assumed that there must be lots of different sources of global temperature records and that the system used to gather and collate the temperature data must be very robust and comprehensive. Its turns out that such assumptions wouldn’t be wholly correct. There are not that many systems and they mostly use the same data sources and the systems for gathering and processing the data so as to produce those neat graphs showing the warming can be surprisingly flakey – largely as we shall see because of the inherent poor or incomplete data available. This article is just an overview of who does what in terms of producing a global temperature record and what sort of data is used.
The systems for gathering data about global temperatures going back in time are based on either data gathered from ground based thermometers from around the planet or data from satellite readings.
These two ways to gather temperature data measure different things. The ground based thermometers measure temperature at ground level while the two satellite systems measure temperatures high in the atmosphere.
The satellite system only started in 1978, which is around the time the current warming phase started after the cooling phase between 1940 and 1975, so it has only generated data about the last three (warming) decades.
Only the land based temperature system can be used to compare the last three decades with earlier instrument measured temperature and therefore the land based thermometer records have great weight in the discussion about climate change and the history of the climate in the last couple of centuries.
Currently, the longest-running thermometer temperature record is the Central England temperature data series, that starts in 1659.
The longest-running quasi-global record starts in 1850.
There are not many global temperature records or databases. The land based record systems are as follows:
The Met office’s Hadley Centre in the UK maintains the HADCRUT3, a global surface temperature dataset. Hadley works very closely with the University of East Anglia Climate Research Unit (CRU) which was the source of the leaked documents in the so called Climategate affair.
NASA maintains GISTEMP, which provides a measure of the changing global surface temperature with monthly resolution for the period since 1880. GISS is home of scientist James Hansen a very active campaigner in support of the theory of catastrophic man made climate change driven by C02.
The National Oceanic and Atmospheric Administration (NOAA) maintains the Global Historical Climatology Network (GHCN-Monthly) data base contains historical temperature, precipitation, and pressure data for thousands of land stations worldwide.
The United States National Climatic Data Center (NCDC) also maintains a temperature record since 1880.
All these centres share and use almost the same data.
The temperature data for these records come from measurements from land stations and ships. On land, temperature sensors are kept in a Stevenson screen or a maximum minimum temperature system (MMTS). The sea record consists of surface ships taking sea temperature measurements from engine inlets or buckets.
The two other global temperature records use data from satellite readings and these two tend to use more or less the same data but use different systems to process and interpret it. The two satellite records are:
UAH – The University of Alabama, Huntsville
home of the scientists Roy Spencer with his colleagues including John Christy of NASA both of whom tend towards the sceptics camp and there is a video of really interesting lecture by John Christy, here.
RSS – Remote Sensing Systems in Santa Rosa, California, a company supported by NASA for the analysis of satellite data.
Satellite temperature measurements have been obtained from the troposphere since late 1978. Satellites do not measure temperature as such. They measure radiances in various wavelength bands, which must then be mathematically inverted to obtain indirect inferences of temperature.The resulting temperature profiles depend on details of the methods that are used to obtain temperatures from radiances. As a result, different groups that have analysed the satellite data to calculate temperature trends have obtained a range of values.
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