How reliable is the global temperature record? Part two

Let’s introduce the characters in our story.

First, the satellite measurements.  Back in part 1, we found that satellites infer atmospheric temps by measuring microwave emissions from oxygen molecules.  There are two primary groups working with satellite data.  One is at the University of Alabama at Huntsville (UAH) and the other is Remote Sensing Systems (RSS); both work with the data from satellites to produce a temperature record.  Other groups are working with this data as well, but RSS and UAH are the major players. There is a lot of interesting physics and climate stuff here, but the data only go back to late 1978, and quite a substantial amount of processing is necessary to create the satellite temperature record.  The MSU post from Tamino’s Open Mind blog has a nice summary of the satellite info, albeit from 2007.  I plan to get back to this data later in our series.

The ground record of temperature comes from a variety of sources and are turned into monthly global-average readings by three independent research groups:

  1. The Met Office, in collaboration with the Climate Research Unit (CRU) at the University of East Anglia in the UK.
  2. The Goddard Institute for Space Sciences (GISS), part of the National Aeronautics and Space Administration in the US.
  3. The National Climate Data Center (NCDC), part of the National Oceanic and Atmospheric Administration in the US.

These three groups use different methods to collect and process the temperature readings in calculating the global-average numbers.  Their results are similar and they are in close agreement on the decade to decade trends.

The data sources for the Big Three come from different sources with each source having its own characteristics. It is generally agreed that reasonably reliable surface temperatures with wide geographic coverage begin around 1850.  Some records begin earlier, but have restricted geographic coverage.

The longest temperature record in use is the Central England Temperature record, dating from 1659 to the present.  It consists of monthly averages from 1659 to 1772, and daily averages from November 1772 onward.  The Met Office maintains the official CET record at the Hadley Centre.  In addition, the Hadley Centre maintains HADCRUT3, a global temperature dataset dating from 1850.

NASA maintains GIStemp, a record which provides monthly averages with wide geographic coverage from about 1880, although some records go back to the 1770s.  NOAO is responsible for the Global Historical Climatology Network (GHCN), which contains records as early as 1697. Widespread gridded monthly average temperatures are available from January 1880.  GHCN also has precipitation and pressure readings.  The US portion of the GHCN is the United States Historical Climate Network (USHCN) data, maintained by the NCDC and adjusted independently of the worldwide data.

Finally, the important antarctic records come from the Scientific Committee on Antarctic Research (SCAR) via the Reference Antarctic Data for Environmental Research (READER) program.  There are few fixed surface stations in Antarctica, and most stations have operated for short times, appearing and disappearing, leading to a very interesting data analysis program.

Next we’ll look at the problems facing the keepers of the datasets.

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