A. What does Global Warming or Global Cooling Mean.

There are numerous organizations that measure and process temperature data in determining the average global temperature anomaly.  The IPCC (2013) has referenced four methods as CRUTEM4 (part of HadCRUT4), CHCN (a group maintain data sets at NOAA), GISS (NASA Goddard Space Flight Center) and Berkeley (mathematical manipulation of data). These methods are not independent because they use a lot of the same input observation data.  [Hansen J, et al (2010) Global Surface Temperature Change, Geophysics, Vol 48 Issue RG4004. Pgs. 1-29]  

“These analyses are not independent as they must use much the same input observations.” Hansen page 1:

The differences in the conclusions are shown in Table 2.4 at pg. 187 of IPCC 2013 for selected time periods.   

The above table illustrates that slight differences in each method for several selected periods. Quorvita has selected HadCRUT4 to review in more detail as it appears to be the most used and employs the most reliable measuring devices. 

What they do, where they do it, and how the measurements are made is not a easy task.   It is best to quote the applicable sections of the the HadCRUT4 procedure.  This is published on their website.  

“HadCRUT4 is a global temperature dataset, providing gridded temperature anomalies across the world as well as averages for the hemispheres and the globe as a whole. CRUTEM4 and HadSST3 are the land and ocean components of this overall dataset, respectively.”

 “These datasets have been developed by the Climatic Research Unit (University of East Anglia) in conjunction with the Hadley Centre (UK Met Office), apart from the sea surface temperature (SST) dataset which was developed solely by the Hadley Centre. These datasets will be updated at roughly monthly intervals into the future. Hemispheric and global averages as monthly and annual values are available as separate files.”

 The CRUTEM4 is described as:

“CRUTEM is a dataset derived from air temperatures near to the land surface recorded at weather stations across all continents of Earth. It has been developed and maintained by the Climatic Research Unit since the early 1980s, with funding provided mostly by the US Department of Energy. The lead scientist for most of this work was Professor Phil Jones, though many colleagues have also contributed.”  [https://crudata.uea.ac.uk/cru/data/crutem/ge/]

HadSST3 is described as:

“The Met Office Hadley Centre’s sea surface temperature data set, HadSST3 is a monthly global field of SST on a 5° latitude by 5° longitude grid from 1850 to date. The data have been adjusted to minimise the effects of changes in instrumentation throughout the record.” [https://www.metoffice.gov.uk/hadobs/hadsst3/]