- HadCRUT4* and the NASA GISS LOTI time temperature series, that are based on surface thermometers, show a high level of agreement (Figure 1). Offset differences between the two is roughly 0.2˚C which is largely inconsequential in the bigger picture. One curious discrepancy is that GISS LOTI temperatures have continued to rise since 1998 while HadCRUT4 is more flat.
- The UAH and RSS satellite based time temperature series also show a high degree of agreement largely within 0.1˚C.
- A linear regression through the HadCRUT4 data shows a long-term warming trend of 0.48˚C per century. A linear regression through the UAH satellite data shows warming of 1.11˚C per century. The much higher rate of warming is because the satellite record, that begins in 1980, only samples the recent up leg of what is fluctuating time temperature data (Figure 1).
- Surface thermometers compared with satellite data also show a high degree of agreement, which is a credit to all the scientists that work on compiling these fundamentally important data sets. The differences are subtle, but the surface thermometer series and satellite data are diverging with time over the relatively short 35 years of satellite data. In this time frame, the surface thermometers are warming at a rate of 0.42˚C per century more rapidly than the satellite data. This is a substantial bias that requires an explanation. This bias is sufficient to send surface thermometers into record breaking territory while the satellite data continues to move sideways and down since 1998.
* all data sources and acronyms are explained at the end of the post
Figure 1 GISS LOTI is biased to higher T anomalies than HadCRUT4. This is largely down to the different base periods chosen for calculating anomalies; 1951-1980 for GISS and 1961-1990 for HadCRUT4. The linear regression through HadCRUT4 is largely matched by parallel rising tops and bottoms (dashed lines). GISS LOTI is rising at 0.69˚C per century (not shown), appreciably higher than HadCRUT4, and caused in part by the recent acceleration in the GISS index.
With the Paris climate and global energy system talks looming there is a lot of interest in whether or not the Earth’s atmosphere (lower troposphere to be precise) is still warming. For years now, there has been talk of “a pause” in warming since 1998. But now, just in time, there is a flurry of stories about record temperatures being set in England (during one of the coldest summers in recent times), and that 2015 is heading to be the warmest year ever (since records began). The climate science community gloats over rising temperatures; evidently more concerned about the reliability of their models and research grants than they are about the well fare of the Human Race and Earth ecosystems. On the other side of the coin, the sceptics watch the Sun approach a grand solar minimum and hope that the Seine freezes over in December.
I decided it was time to take a closer look at the temperature records upon which all the propaganda is based. A main message I wish to send is that the differences between the 4 temperature records examined are small and subtle and given the uncertainties, decisions about our energy future are being made in an information framework that is far from certain. The opinion of anyone espousing 97% certainty should in the circumstances be disregarded.
There are at least 5 compilations of surface thermometer records. In this post I examine two of them, the NASA GISS LOTI and HadCRUT4 (Figure 1). These reconstructions are using largely the same data archive but the application of different methodologies means that the various groups arrive at somewhat different answers.
One of the key differences is selection of base period for the calculation of anomalies (Figure 1) . The average temperature of the base period is deducted from the measured temperatures for all months to determine the anomaly and since different base periods are used this results in GISS being linearly displaced to higher temperatures than HadCRUT4 (Figure 1). But that is not all that is going on.
Figure 2 GISS LOTI minus HadCRUT4. The main observations are: 1) the positive bias in GISS most likely comes down to the selection of different base periods; 2) the differences are small, mainly confined to +015 and -0.05˚C; and 3) the cyclical variance, especially between 1920 and 1970 requires an explanation, but that is beyond the scope of this post.
Deducting HadCRUT4 from GISS LOTI quantifies the residuals as shown in Figure 2. It is a rather curious pattern. Most of the dT is confined to +0.15 and -0.05˚C (±0.1) which in the larger picture is a rather small difference. Since the difference is small I will not try to explain it. But it is worth noting that since 1970 GISS LOTI first diverged, then converged and is now diverging again from HadCRUT4. The recent divergence during the last 15 years is evident in Figure 1 where NASA GISS can be seen to be warming at a higher rate than HadCRUT4.
The average warming rates are:
GISS LOTI 0.69˚C per century
HadCRUT4 0.48˚C per century
The difference is in fact small and likely within the uncertainty. I will return to these surface thermometer records following a description of the satellite data.
The procedure for measuring the temperature of the lower troposphere from space employing microwave data is complex. The satellites that do this are in decaying orbits, burn up and need to be replaced on a regular basis. Roy Spencer at UAH provides a good description.
There have been several satellites and the data are merged into a single data set. This data is analysed by two separate groups. One led by Roy Spencer at the University of Alabama, Huntsville (UAH) and the other by Remote Sensing Systems (RSS). The temperature records are compared in Figure 3.
Figure 3 Comparison of the two satellite records. They are very closely alined, with dT lower than 0.15˚C (Figure 4).
Figure 3 shows how the two analyses are closely alined but are offset by about 0.15˚C, presumably because of calibration and or normalisation differences (Figure 4). The gradients are identical (1.1 v 1.2˚C per century). The satellite data is often used to argue that there has been no warming since 1997, and indeed a regression through the post-1997 data has a negative gradient. The last year plotted is 2014, but it is plain to see that the satellite data is nowhere close to recording record high temperatures. The warmest year remains 1998 followed by 2010.
Figure 4 dT between RSS and UAH determined by subtracting UAH from RSS (Figure 3).
Comparison of Thermometers and Satellites
Having set the scene, I now get to the main point of the post and that is to compare the thermometer and satellite records. To do this I have removed the small biases described above by re-normalising the data so that the mean of the 5 year period 1980 to 1984 = 0.00˚C. To do this the following adjustments have been applied:
GISS LOTI -0.242˚C
RSS + 0.059˚C
This has the effect of making all of the indexes begin at the same datum point of 0.0˚C at the beginning of the time series. It does not affect structure or gradient of the data. The result shown in Figure 5 shows a number of things: 1) the two satellite records and the two thermometer records are very closely alined, 2) in a general sense there is good agreement between thermometers and satellites and 3) it is evident that the thermometers and satellites are diverging (Figures 6 and 7).
Figure 5 The two satellite and two thermometer records compared. One should not lose sight of the fact that these two very different approaches to measuring the mean temperature of the lower troposphere are providing quite closely alined results.
Figure 6 A simplification of Figure 5 showing the means of thermometers and satellites. While the differences are small and subtle, the outcome is not. Thermometers mark 2014 as the warmest year, satellites show 2014 as nothing out of the ordinary.
Simplifying one stage further, Figure 6 shows the simple arithmetic means of the thermometer and satellite data and shows that since 1980, the thermometer record has been warming +0.4˚C per century more than the satellite record. This is a small difference but it is significant because it pushes the surface thermometers into the territory of “record warmth” while the satellites are nowhere close to recording new temperature highs. Note that the warming trends are for the steep up leg since 1980 (Figure 1) and should not be extrapolated into the future since we know that natural oceanic cycles (e.g the Atlantic Multi-decadal Oscillation or AMO) will drive temperatures sideways or down at some point in the future.
Figure 7 Subtracting satellite temperatures from thermometers provides this picture. Up until 1998 there is no clear bias but after that the surface thermometers go into over drive. But note the absolute differences are tiny, about 0.15˚C.
Finally, Figure 7 shows the difference between the thermometer and satellite trends (Figure 6) and shows that the thermometers have been steadily diverging from the satellites since 1980, especially since 2004, with two notable exceptions during the big El Nino years of 1998 and 2010 where the satellites run warmer than the thermometers. Removing these two years from the regression, the R^2 improves to 0.51.
The origin of the trends in Figures 6 and 7 require an explanation. Either the satellite or thermometer records are biased in some way. Note that the differences between thermometers and satellites is minute – only +0.15˚C in 2014 and when you consider that this is supposed to represent the average temperature of the lower troposphere the difference is trivial. What is not trivial is the trend through the data which as already mentioned is sufficient to have thermometers recording record temperatures while the satellite record since 1998 is actually trending down. This minute difference will be used by the climate science community to argue for vast penalties to be imposed upon humanity in the Paris talks. The stakes could hardly be higher.
My own prejudice, it is the thermometer record that is subtly biased for a number of reasons. First, the climate science community seems over eager to find warming wherever they look and to exaggerate dubious observations. A good example of this would be UK MET office claims of new record temperatures at Heathrow Airport in July of this year which seems likely to have been caused by hot air from a jet. Credible scientists would not seek to use or publicise data from such a dubious source as Heathrow Airport. The surface thermometer record is also fraught with problems one being that many records are unreliable. Rather than discarding unreliable data the climate science community choses instead to try and correct them employing dubious homogenisation algorithms. This opens the door to data manipulation. And for example, in the case of Iceland, well curated records have been changed creating the aura of record warmth on that island that quite simply does not exist. Finally, I believe that land surface changes such as deforestation and irrigation may impact surface thermometers in a way that goes beyond the well documented urban heat island effect. This in essence may create near surface anthropogenic global warming that is not caused by greenhouse gasses and may be viewed as benign.
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