The bottom of the data page for the GISS Land-Ocean Temperature Index used to (past tense) include a useful reference. But that reference was deleted in January 2016 and has been gone ever since, as far as I can tell.
The data page for the GISS Land-Ocean Temperature Index used to contain a statement that began:
Best estimate for absolute global mean for 1951-1980 is 14.0 deg-C or 57.2 deg-F, …
In other words, it was a factor for converting their annual anomaly data, which are referenced to the based period of 1951-1980, from anomalies to absolute temperatures.
The statement continued:
…so add that to the temperature change if you want to use an absolute scale
(this note applies to global annual means only, J-D and D-N !)
Below that, GISS provided a few examples, as can be seen in a screencap of a December, 2015 data page, Figure 1, taken from a WaybackMachine-archived webpage here.
A month later, the factor for converting their data in anomaly form to absolute form was gone, magically disappearing. As far as I know, it’s been gone since then. To confirm the disappearance, Figure 2 includes a screencap of the bottom of the GISS January 2016 data page from the WaybackMachine archive. See the webpage here.
GISS continues to list that absolute value on their The Elusive Absolute Surface Air Temperature (SAT) webpage here. See the Q&A that reads (my boldface):
What do I do if I need absolute SATs, not anomalies?
A. In 99.9% of the cases you’ll find that anomalies are exactly what you need, not absolute temperatures. In the remaining cases, you have to pick one of the available climatologies and add the anomalies (with respect to the proper base period) to it. For the global mean, the most trusted models produce a value of roughly 14°C, i.e. 57.2°F, but it may easily be anywhere between 56 and 58°F and regionally, let alone locally, the situation is even worse.
Hmm, “…the most trusted models produce a value of roughly 14°C…” Curiously, for the period of 1951-1980, the average absolute global mean surface temperature is 15.1 deg C for the 6 ensemble members of the GISS Model E2 that are stored in the CMIP5 archive with historic and RCP8.5 forcings. If you wish to confirm that little tidbit of information, you can download the monthly global surface air temperatures (TAS) from the GISS Model E2 in absolute form for those ensemble members stored in the CMIP5 archive with those forcings (and others) at the KNMI Climate Explorer. Isn’t the GISS Model E2 GISS’s “most trusted” model?
SIDE NOTE TO GAVIN: Maybe GISS should consider updating that Q&A to reflect the outputs of the latest and greatest GISS climate models.
NOTE REGARDING MY USE OF THE TERM ABSOLUTE TEMPERATURE
The term Absolute is commonly used by the climate science community when discussing Earth’s surface temperature when they aren’t using anomalies. See the quotes from GISS above.
I’ll let you speculate as to why GISS deleted that useful adjustment factor.
That’s it for this post. Have fun in the comments and enjoy the rest of your day.
STANDARD CLOSING REQUEST
Please purchase my recently published ebooks. As many of you know, this year I published 2 ebooks that are available through Amazon in Kindle format:
- Dad, Why Are You A Global Warming Denier? (For an overview, the blog post that introduced it is here.)
- Dad, Is Climate Getting Worse in the United States? (See the blog post here for an overview.)
To those of you who have purchased them, thank you. To those of you who will purchase them, thank you, too.
Reblogged this on Climate Collections.
My only idea is that the published data is a sum of anomalies from different sources. If the number of sources changes in time, it is not possible to state one definite reference value…?