With the 2015 lower troposphere temperatures in, NASA and NOAA have declared without any caveats or doubts, that 2015 was the warmest year since records began. This short post updates my charts that compare satellite with surface thermometers temperatures. The differences between the two methodologies are in fact tiny and subtle. According to satellites, 2015 was the third warmest year, lagging 1999 by a fair margin. The main material difference, therefore, is that the satellite record would deprive the scaremongers at NASA and NOAA of their eye popping headlines.
Figure 1 Surface thermometer (GISS LOTI and HadCrut4) and satellite (UAH and RSS) records compared. It is plain to see that surface thermometers set a new record in 2015 while the satellites did not.
In this post I am looking at two of the surface thermometer records (GISS LOTI and HadCrut4) and the only two versions of the satellite record (UAH and RSS). The surface thermometer models are based to a large extent on the same surface thermometer data base where air temperature is measured over land and sea surface temperature (SST) is measured over the oceans. The results are area weighted with the SSTs contributing about 70% of the total. The satellite models are based on the exact same satellite recordings. We will see that there is no material difference between GISS LOTI and HadCrut4 and no material difference between UAH and RSS.
The satellite record begins in 1980 and it is only the post-1980 parts of the records that are considered here. The records use different base periods from which temperature anomalies are calculated and this hinders direct comparisons. This is overcome by rebasing each series to 1980-1984 = 0˚C. The online data sources and how to find them are detailed in the appendix.
Figure 2 The surface thermometer records from NASA GISS and UK Met Hadley are in excellent agreement. The notorious pause, 1997 to 2014 has now been busted and these records now present a picture of continuous warming across this 36 year period.
Figure 3 The satellite record as interpreted by the University of Alabama (UAH) and Remote Sensing Systems (RSS) are also in excellent agreement. As we shall see, the difference between this and surface thermometers is small and subtle. The satellite record is in two parts. 1980 to 1997 is largely flat. 1998 to 2015 is largely flat. A step change took place 1997 to 1998. The material difference with thermometers is that 2015, an el Nino year, has not come close to setting a new record.
Figure 4 Averaging the two thermometer records and the two satellite records provides this simplified picture. The regression shows that thermometers are warming at 0.45˚C per century more than satellites. This really is a trivial amount.
Figure 5 Subtracting satellites from thermometers provides this picture of diverging records. The divergence should make all scientists curious since it raises some vital questions. Is the near surface (thermometers) actually warming more rapidly than the bulk lower troposphere (satellites)? Or is there a systematic bias / error in one or both of the data recording mechanisms?
Standing back to take a broader view, one thing strikes me as very odd and that is the different response of the satellites and thermometers to the three large el Nino events in 1998, 2011 and 2015. In particular, the satellites registered much higher temperatures during the 1998 event than thermometers, reversing the normal bias. In 2011, satellites recorded slightly higher temperatures. And in the 2015 el Nino thermometers registered significantly higher temperatures than satellites.
For those thinking that my introductory comments about eye popping headlines was over the top, here it is.
NASA, NOAA Analyses Reveal Record-Shattering Global Warm Temperatures in 2015
It’s not exactly measured scientific jargon from the pride of US science and engineering institutions, is it? The press release does at least mention satellites:
NASA monitors Earth’s vital signs from land, air and space with a fleet of satellites, as well as airborne and ground-based observation campaigns.
You’d have thought NASA and NOAA, who have one foot on the ground and the other in space, would at least have mentioned the discrepancy between land based and space based measurements and offered some explanation.
I’ll leave you with this video of Dr Gavin Schmidt (Director of Goddard Institute of Space Studies) and Dr Roy Spencer who runs the UAH satellite data set together with Dr John Christy.
Acronyms, Abbreviations and Data Sources
HadCRUT4 stands for Hadley Research Centre at the UK Met office and Climate Research Unit of the University of East Anglia and Temperature and version 4. Data downloaded from this link:
NASA is the US National Aeronautics and Space Administration. GISS is the Goddard Institute for Space Studies. LOTI is the Land Ocean Temperature Index. Data downloaded from this link:
UAH is the University of Alabama, Huntsville where Roy Spencer and John Christie are the curators of the satellite microwave data. Data for V6 were downloaded from this link:
Selecting the file tltglhmam_6.0beta3
RSS is Remote Sensing Systems, the other curator of the satellite microwave data. Data were downloaded from this link:
Clicking on FTP Air Temp Time Series and then selecting the first file called