Latest global monthly temperature estimate: HadCRUT3 and 4
Global monthly average lower troposphere temperature since 1979 according to Remote Sensing Systems (RSS). This graph uses data obtained by the National Oceanographic and Atmospheric Administration (NOAA) TIROS-N satellite, and interpreted by Dr. Carl Mears (RSS). The thick line is the simple running 37 month average, nearly corresponding to a running 3 yr average. The cooling and warming periods directly influenced by the 1991 Mt. Pinatubo volcanic eruption and the 1998 El Niño, respectively, are clearly visible. Click here for a description of RSS MSU data products. Please note that RSS January 2011 changed from Version 3.2 to Version 3.3 of their MSU/AMSU lower tropospheric (TLT) temperature product. Click here to read a description of the change from version 3.2 to 3.3, and previous changes. Last month shown: July 2013. Last diagram update: 7 August 2013.
GISS – Goddard Institute for Space Studies and home of James Hansen,
Hadley Centre – British Meteorological Office research centre
UAH – The University of Alabama, Huntsville, home of Roy Spencer with his colleagues including John Christy of NASA and
RSS – Remote Sensing Systems in Santa Rosa, California, a company supported by NASA for the analysis of satellite data.
The first two groups use ground based data where possible with a degree of commonality. However since 70% of the surface of the earth is ocean and it is not monitored in a detailed manner, various procedures with possibly heroic assumptions and computer modelling, are followed to fill the ocean gap.
The last two groups use satellite data to probe the atmosphere and with the exception of the Polar Regions which are less than 10% of the globe, they get comprehensive coverage.
One question is of course are the two groups measuring the same temperature? After all the satellite looks down through the atmosphere, while the ground stations are exactly that.
There is an important distinction to be made between measuring the temperature and measuring the change in the temperature. Since the interest is in changing temperatures then what is called the global temperature anomaly is the starting point.