Notes On The GISTEMP Ratio Of Land To Sea Surface Temperature Data
Guest post by BobTisdale
Over the past few days there has been some blogosphere buzz about the apparent ratio of Land Surface Temperature (LST) Data used in the GISTEMP combined land and sea surface temperature data with 1200km smoothing. I’ll provide a few comparison graphs to explain.
Figure 1 includes a time series graph of the Hadley Centre’s HADCRUT3 Combined Surface Temperature product, from January 1982 to April 2010. Also included is the weighted average of the two datasets that make up the HADCRUT3 data, with the weighting of 27% LST [CRUTEM3] and 73% Sea Surface Temperature (SST) [HADSST2]. Those weightings were required to match the linear trend of the weighted average to the linear trend of the HADCRUT3 combined product. The weighting makes sense, since the global oceans represent about 70% of the surface area of the globe.
http://i28.tinypic.com/2yoe59f.jpg
Figure 1
Figures 2 and 3 provide similar comparison graphs. Figure 2 shows the NCDC combined surface temperature product and the weighted average of its LST and SST components. To align the linear trends, the weighting required for the components of the NCDC product was also 27% LST data and 73% SST data. Figure 3 shows the GISTEMP product with 250km radius smoothing. For this GISTEMP product, the weighting required for the components was 28.5% LST data and 71.5% SST data. Again, the relationships of the SST and LST data make sense.
http://i26.tinypic.com/2qmi3yh.jpg
Figure 2
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http://i25.tinypic.com/1rx6v7.jpg
Figure 3
Here’s the curiosity. It appears in the GISTEMP Product with 1200km radius smoothing when we apply the same component weighting (28.5% LST data and 71.5% SST data) that we had used on the other GISTEMP combined product. The weighted average of the components of the GISTEMP combined product with 1200km radius smoothing has a significantly lower trend than the actual GISTEMP data. This can be seen in Figure 4.
http://i28.tinypic.com/9jot4x.jpg
Figure 4
In order to achieve the same linear trend as the GISTEMP combined product with 1200km radius smoothing, the components have to be weighted with 67% LST data and 33% SST data, almost reversing the ratio of the areas of global oceans and continental land masses.
http://i30.tinypic.com/p9g5d.jpg
Figure 5
Figure 6 is a map illustrating the GISTEMP LST data (trends) from 1982 to 2009. Note how the GISTEMP LST data extends out over the oceans. This is not the case for their combined product, because GISS masks the LST data over the oceans in its combined product. So in order to properly create a weighted average of GISTEMP land and sea surface temperature data with 1200km radius smoothing, the land surface data where it extends out over the oceans would first need to be masked.
http://i26.tinypic.com/4ieop2.jpg
Figure 6
A NOTE ON THE DIVERGENCE BETWEEN GISS AND THE OTHER DATASETS
Much of the divergence between GISTEMP and the Hadley Centre and NCDC combined surface temperature products is likely caused by the fact that GISS deletes SST data in the Southern and Arctic Oceans and replaces it with LST data, which has a significantly higher linear trend than the SST data it replaces. This was discussed in the post GISS Deletes Arctic And Southern Ocean Sea Surface Temperature Data.
ANOTHER CURIOSITY
It can also appear that GISS extends LST data out over the oceans in areas other than those with seasonal sea ice. In fact, I made this mistake in a comment at Lucia’s The Blackboard this morning. Refer to my Comment#49191 at the bottom of her post NOAA: Hottest June in Record. This illusion can be seen in the following .gif animation of GISTEMP trend maps for the period of 1982 to 2009. The April trend is presented in Figure 7. Note how, in the highlighted area of the North Atlantic, there are differences between the SST trend and the trend of the GISTEMP combined product with 1200km radius smoothing. The Faroe Islands are located between Scotland and Iceland, and GISS uses station data there, so that explains the differences in that area. But what of the area of the North Atlantic west of Ireland and south of Iceland, with the approximate coordinates of 50N-60N, 20W-15W? There aren’t any islands there with weather stations.
http://i29.tinypic.com/2i0vhif.jpg
Figure 7
In its GISTEMP LST products, GISS also includes surface station data identified as Ship followed by a letter; that is, “Ship J”, “Ship R”, etc. Refer to Figure 8. These can be found using the station locator feature on the GISTEMP Station Data webpage.
http://i32.tinypic.com/2i09k7r.jpg
Figure 8
Here’s a link to the webpage presented in Figure 8.
I have found little to no information on these GHCN “ship stations”. Are they presenting SST or Nighttime Marine Air Temperature? Dunno. They may have served a purpose when GISS first prepared their GISTEMP product due to the sparseness of SST data in the early SST datasets, but now, these “ship stations” only add an unknown bias to well-documented optimally interpolated SST data. (And if they don’t add a bias either way, then there’s really no reason to have them. All they do is add confusion.)
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yes. Not only was the discrepancy obvious, even with the attempt to pretend that oceanic areas that were cooling were ‘hot’, but the extension of land temperatures onto the oceans was retarded.
Bob, you’re a complete denier paid by Exxon Mobil and BP… go swim in that hot, boiling oil polluted hurricane basin!
Oh, and there was something on the Blackboard a while back about how GISS does not weight it’s land temps by hemisphere… not sure if that would answer your question… but it shows how incompetent the boys at GISS are if they publish numbers and they didn’t consider how there are different amounts of landmass in each hemisphere.
If the data shows warming, attack the data, and the methods used to collect and analyse them. If the data shows cooling, no problem then!
We must present scarry senarios since the summit in Mexico is coming up….must get an agreement…/sarc off.
Has anyone looked at the siting of the Faroe Islands station?
WRT ships.
In my code these ships recieve ZERO weighting, they are dropped.
Eek, Zeke!
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I wrote up the whole land/ocean ratio thing on my blog a month ago:
http://knowledgedrift.wordpress.com/2010/06/16/giss-global-temperatures-and-math/
I did that with every 5th year of annual data, but I have since done it with the monthlyy data from 1880 and got the same result. However, while doing that analysis, I discovered something even more interesting. In addition to the changing weighting between land and ocean which isn’t anywhere near proper math, I also discovered something very odd about the SST data they use. Is it NOAA or is it Hadl/Reyn?
Answer; It appears to be both. They slide the warmer Hadl/Reyn SST data into the places where it would go undetected if you didn’t break the grid points down to a very detailed level. But I did. I only looked at the 250 Km smoothing, not the 1200, but it seems pretty plain that gridpoints that report a merged land/ocean anomaly are calculated from the warmer Hadl/Reyn SST from 1982 on:
http://knowledgedrift.wordpress.com/2010/07/17/games-from-giss/
Has anybody found the warm CO2 greenhouse roofing placed over the equator by all the computer models? Isn’t the missing CO2 greenhouse roofing proof enough the whole theory is composed of falsehoods? In normal times it would disprove.
http://rankexploits.com/musings/2010/the-great-gistemp-mystery
In other words, the GISTEMP global gridded land anomaly is not weighted by the ‘land area fraction.’
———————–
The ship data does not come from GISTEMP but GHCN
(I read this out of the ghcn v2.mean but you can get the same info in GISS station data page)
80099906001 SHIP I 59.00 -19.00 -999 0 R -9
80099907001 SHIP J 52.50 -20.00 -999 0 R -9
80099909001 SHIP L 57.00 -20.00 -999 0 R -9
SHIP I has data in 1948-1975
SHIP J has data in 1948-1975
SHIP L has data in 1975-1989
SHIP L is dropped from the processing (noted on the GISTEMP station page and confirmed in the short.station.log output in GISTEMP step 3)
As to the Fig 7 flip chart, most of the NAtl bobble goes away with a smoothing of 250km.
And just a follow up –
If you do a ‘GISS’ only graph (“land” only) for 1970-75, you will see some spots in the mid North Atlantic south of Iceland and west of Ireland for Ships I and J.
Do it again for 1976-1980, and Ships I and J are gone.
Steven Mosher wrote: “WRT ships. In my code these ships recieve ZERO weighting, they are dropped.”
But they appear to influence the trends. Scroll up to Figure 7 and note the white dot that appears in the GISTEMP combined product in the extreme Northeast Pacific, about 50N & 145W, but is not there in the SST data. That should be “Ship P”.
http://data.giss.nasa.gov/cgi-bin/gistemp/findstation.py?lat=50.0&lon=-145.0&datatype=gistemp&data_set=1
Bob
Just look at Fig 4 – at the left you will see that the data shows anomalous cooling. But I know that’s not what you mean.
Perhaps you could enlighten us with all this data that shows cooling. I’m sure the experts here would be happy to comment on that too.
You see, what the vast majority of people here want to see is simply temperature data that can with stand scrutiny from questioning scientific minds. They want to see better recording, more realistic modelling and unbiassed reporting of the outcomes, with transparency throughout.
I suspect they also would like to see a little more humility from many of the leading proponents with regard to the uncertainties in their work.
It worries me immensely when leading scientists and advisors to governments say warming has to be causd by man’s activities because we can’t think of anything else that would cause it! If that view had prevailed throughout the history of science we would still be bleeding and leeching to induce a balance of humo(u)rs in the body, light would still be carried by the luminiferous ether and the earth would still be the centre of the universe.
I will remind you that the people who caused science to move forward were the questioners. The deniers were those refused to question the accepted truths of the time (aka the concensus view).
davidmhoffer says: “They slide the warmer Hadl/Reyn SST data into the places where it would go undetected if you didn’t break the grid points down to a very detailed level. But I did. I only looked at the 250 Km smoothing, not the 1200, but it seems pretty plain that gridpoints that report a merged land/ocean anomaly are calculated from the warmer Hadl/Reyn SST from 1982 on…”
David, first, “Hadl/Reyn SST” are two separate SST datasets. GISS notes this in numerous papers and webpages. The “Hadl” portion is HADISST, which they use from January 1880 to November 1981. The “Reyn” portion is Reynolds (OI.v2) SST data, which they use from December 1981 to present. Refer to the Ocean data source description under “Input Elements” here:
http://data.giss.nasa.gov/gistemp/maps/
Second, the Reynolds (OI.v2) SST dataset does have a higher trend than HADISST over the period they use the Reynolds SST data, but the difference in the trends is minimal, 0.01 deg C/decade:
http://i32.tinypic.com/2kocoy.jpg
With respect to your first linked post, a few questions? If, for example, land surface data does not exist for Antarctica prior to 1950, how is that an error on the part of GISS? Second, when you were analyzing your percentages of land to ocean data, did you mask where the land surface data extends out over the oceans?
Bob says: “If the data shows warming, attack the data, and the methods used to collect and analyse them. If the data shows cooling, no problem then!”
Hmm. Did you read the post? I don’t believe I attacked the data, methods or analysis.
Peter Plail says: “Just look at Fig 4 – at the left you will see that the data shows anomalous cooling. But I know that’s not what you mean.” And continued, “Perhaps you could enlighten us with all this data that shows cooling. I’m sure the experts here would be happy to comment on that too.”
Figure 4 doesn’t show cooling. It shows gradual increases in temperature from 1982 to present that is impacted by volcanic eruptions and ENSO events to create the year-to-year variability. The data is below zero in the early years due to the base years used for anomalies.
Weather ships : ‘fixed’ location floating weather stations for aviation
http://en.m.wikipedia.org/wiki/Weather_ship?
(a valid use of wikipeadia ! )
Some history here : http://iancoombe.tripod.com/id56.html – includes some detail of the OBS carried out
Ron Broberg wrote, “In other words, the GISTEMP global gridded land anomaly is not weighted by the ‘land area fraction.’ ”
Thanks for the clarification, but I didn’t write or imply that it was. This post was about the curiosity found by other bloggers. I attempted to explain why they were seeing the significant disparity in the ratio of land to ocean data.
You wrote, “As to the Fig 7 flip chart, most of the NAtl bobble goes away with a smoothing of 250km.”
I guess it depends on one’s definition of “most of”:
http://i30.tinypic.com/10pwtua.jpg
You wrote, “If you do a ‘GISS’ only graph (“land” only) for 1970-75, you will see some spots in the mid North Atlantic south of Iceland and west of Ireland for Ships I and J… Do it again for 1976-1980, and Ships I and J are gone.”
Thanks, that confirms the dates in your earlier comment, leaving only “Ship R” for the period we’ve been looking at. And it covers the period of 1975 to 1985.
Regards
Data Sources: Ocean
Bob Tisdale,
Yes, HadISST and Reyn are different data sets as specified in the Global Maps web site at GISS which reads:
None: NO ocean temperature data are used
Hadl/Reyn_v2:SST 1880-present
1880-11/1981: Hadley HadISST1, ship and buoy data (Rayner 2000),
12/1981-present: oisst v2, satellite data (Reynolds-Rayner-Smith 2001)
NOAA/ER_v3b:SST 1880-present
NOAA ERSST V3b, ship and buoy data (Smith,Reynolds,et al 2008)
So… If you derive your data from the Global Maps site, what you get is the adjusted version of the data based on Hadl/Reyn for their respective periods of time, OR you get NOAA V3b for the SST data But if you download the raw monthly anomaly data for Land and Combined, the period from 19450 to current clearly reflects NOAA in the combined data with the exception of those grid points that overlap between land and ocean since Dec 1981 which reflect Hadl/Reyn in months when there is no Land station data available.
As to your second question:
“If, for example, land surface data does not exist for Antarctica prior to 1950, how is that an error on the part of GISS? Second, when you were analyzing your percentages of land to ocean data, did you mask where the land surface data extends out over the oceans?”
The fact that land surface data for Antarctica didn’t exist prior to 1950 isn’t an error on the part of GISS. Adding the data since 1950 and calculating the combined global anomaly as if the planet’s land mass suddenly grew by the area of Antarctica while the oceans stayed the same size is. We don’t get more land on the planet by measuring it in more places. No, I didn’t mask where the land surface data extends into the ocean. I used the 250 km smoothing which reduces the problem in the first place, compared the number of land grid points to ocean grid points and concluded that Land was about 6% of the Combined data in 1880 and somewhere over 30% by now. Frank Lasner took a different approach in his post just before yours to calculating the numbers, but also conlcuded that Land data counted for almost nothing in the Combined data set in the early part of the graph and that it increases significantly over time as more land station reporting becomes available while ocean coverage is pretty much static. In brief, Land influence in the combined set increases as more land station reporting becomes available, which accelerates the warming trend in the Combined data. The fact (as you have pointed out) that GISS ignores or deletes SST data if it is reported within a certain distance of (100 km?) of a land station also means that as land station reporting increases over time, SST data decreases, hence biasing the global combined anomaly more heavily toward the generaly larger Land anomalies. I haven’t looked too much at the 1200 km smoothing but I imagine this effect would be more pronounced there than with the 250 km smoothing.
MikeC: You wrote, “Oh, and there was something on the Blackboard a while back about how GISS does not weight it’s land temps by hemisphere… not sure if that would answer your question… ”
I looked into it, and over the period I chose to work with, the differences in linear trends are minimal (0.001 deg C/decade) using Global Combined Land Plus Sea Surface Temperatures with 1200km radius smoothing.
Peter_dtm: Thanks for the link on weather ships. Now the question is, is GHCN presenting NMAT or SST? One would assume NMAT, but…
tarpon says:
July 17, 2010 at 11:06 pm
Has anybody found the warm CO2 greenhouse roofing placed over the equator by all the computer models? Isn’t the missing CO2 greenhouse roofing proof enough the whole theory is composed of falsehoods? In normal times it would disprove.
==========================================================
You would think, since that is a requirement for verifying the computer programs.
Without it, the computer programs are wrong
Last I heard, they said warming is there, because the computer programs say it is, they just can’t find it
thanks Bob!
davidmhoffer says: “But if you download the raw monthly anomaly data for Land and Combined, the period from 19450 to current clearly reflects NOAA in the combined data with the exception of those grid points that overlap between land and ocean since Dec 1981 which reflect Hadl/Reyn in months when there is no Land station data available.”
They do? You’ll need to clarify that, because it made little sense to me.
First, please provide a link to the “raw monthly anomaly data for Land and Combined” data you’re using? Is it this data, which is their standard combined product?
http://data.giss.nasa.gov/gistemp/tabledata/GLB.Ts+dSST.txt
The standard GISTEMP SST dataset is the merger of HADISST and Reynolds data as noted in my earlier reply. This is further clarified in the header of the above link and further confirmed in step 4 of their Sources webpage:
http://data.giss.nasa.gov/gistemp/sources/gistemp.html
FYI. GISTEMP source code and documentation is available here:
http://data.giss.nasa.gov/gistemp/sources/
You wrote, “…since Dec 1981 which reflect Hadl/Reyn in months when there is no Land station data available.”
What months might those be? There’s land surface data available for all months since December 1981:
http://data.giss.nasa.gov/gistemp/tabledata/GLB.Ts.txt
You wrote, “If you derive your data from the Global Maps site…”
I don’t. I use the GISS map-making webpage to plot maps. If I’m looking into their global temperature product, I use their global mean product:
http://data.giss.nasa.gov/gistemp/tabledata/GLB.Ts+dSST.txt
Or their surface station only based data (land surface temperature data):
http://data.giss.nasa.gov/gistemp/tabledata/GLB.Ts.txt
Then, for a post like this that only examines the period after 1982, I also use Reynolds OI.v2 SST data through the NOAA NOMADS website:
http://nomad3.ncep.noaa.gov/cgi-bin/pdisp_sst.sh?lite=
Or if I want to subdivide the globe, I use GISS data available through the KNMI Climate Explorer:
http://climexp.knmi.nl/selectfield_obs.cgi?someone@somewhere%5B
You wrote, “The fact that land surface data for Antarctica didn’t exist prior to 1950 isn’t an error on the part of GISS. Adding the data since 1950 and calculating the combined global anomaly as if the planet’s land mass suddenly grew by the area of Antarctica while the oceans stayed the same size is.”
Huh? Anyone who analyses global temperature data understands, or should understand, when and where data is available, which parts of the data is manufactured by the producer through whatever infilling method they employ, and they should understand the methods used to infill the missing data.
You replied, “I didn’t mask where the land surface data extends into the ocean. I used the 250 km smoothing…”
Then you’re not evaluating the standard GISTEMP product, which uses the 1200km radius smoothing.
You wrote, “Frank Lasner [sic] took a different approach in his post just before yours to calculating the numbers, but also conlcuded that Land data counted for almost nothing in the Combined data set in the early part of the graph and that it increases significantly over time as more land station reporting becomes available while ocean coverage is pretty much static.”
If you’re talking about Frank’s post at Jo Nova’s “Did GISS discover 30% more land in the Northern Hemisphere?…
http://joannenova.com.au/2010/07/did-giss-discover-30-more-land-in-the-northern-hemisphere/
…Frank concluded that he should have masked the land surface data over the oceans in his evaluation. Refer to his July 18th, 2010 at 4:54 pm comment.
You wrote, “The fact (as you have pointed out) that GISS ignores or deletes SST data if it is reported within a certain distance of (100 km?) of a land station also means that as land station reporting increases over time…”
I did not write or imply what you’ve written.
Bob says:
July 17, 2010 at 8:36 pm
“If the data shows warming, attack the data, and the methods used to collect and analyse them. If the data shows cooling, no problem then!”
Attacking the data and the methods is in fact the scientific way of doing things. If the data is fine and the methods to process them are sound they will easily withstand the attack.