tag:blogger.com,1999:blog-2220966763638300672.post6034408851818060455..comments2023-07-29T05:11:23.558-04:00Comments on Climate Observations: GISS Deletes Arctic And Southern Ocean Sea Surface Temperature DataBob Tisdalehttp://www.blogger.com/profile/15462377647970214137noreply@blogger.comBlogger22125tag:blogger.com,1999:blog-2220966763638300672.post-50887101898637094402010-12-21T15:29:07.714-05:002010-12-21T15:29:07.714-05:00Anonymous @ December 21, 2010 1:13 PM: I don'...Anonymous @ December 21, 2010 1:13 PM: I don't believe there's any need for the code if one wanted to determine the actual impact on local temperatures. We know what grids are masked, and the Reynolds OI.v2 data could be used to determine the effective open ocean area and the SST anomalies during a given month.Bob Tisdalehttps://www.blogger.com/profile/15462377647970214137noreply@blogger.comtag:blogger.com,1999:blog-2220966763638300672.post-14659513114179510452010-12-21T13:13:30.350-05:002010-12-21T13:13:30.350-05:00Could you use the ccc-gistemp code to explore what...Could you use the ccc-gistemp code to explore what differences there are between using SST when the relevant area is ice-free vs. Hansen's method?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2220966763638300672.post-58111686321725545852010-12-20T16:56:20.859-05:002010-12-20T16:56:20.859-05:00Anonymous December 20, 2010 12:52 PM:
PS: I jus...Anonymous December 20, 2010 12:52 PM: <br /><br />PS: I just took at quick look through the comments and found that I had linked the preprint of Hansen et al (2010) in the comment before yours.<br /><br />Regards.Bob Tisdalehttps://www.blogger.com/profile/15462377647970214137noreply@blogger.comtag:blogger.com,1999:blog-2220966763638300672.post-50978988469360093112010-12-20T15:49:14.020-05:002010-12-20T15:49:14.020-05:00Anonymous December 20, 2010 12:52 PM: Yes, I'...Anonymous December 20, 2010 12:52 PM: Yes, I'm aware of that discussion in the recent Hansen paper. It, however, does not justify the deletion of SST data when the seasonal sea ice has melted and there is open ocean in areas of the Arctic. That's when SST data should be used.Bob Tisdalehttps://www.blogger.com/profile/15462377647970214137noreply@blogger.comtag:blogger.com,1999:blog-2220966763638300672.post-58778562180192883262010-12-20T12:52:07.592-05:002010-12-20T12:52:07.592-05:00Bob, are you aware of Hansen's latest?
http:/...Bob, are you aware of Hansen's latest?<br /><br />http://www.agu.org/journals/rg/rg1004/2010RG000345<br /><br />Paticularly:<br /><br />"We use ocean temperature change only in regions that are ice free all year (a map of this area is included in Appendix A) because our data set is intended to be temperature change of surface air. Surface air temperature (SAT), measured at heights of 1.25–2 m at meteorological stations, is of most practical significance to humans, and it is usually SAT change that is reported in climate model studies. Change of sea surface temperature (SST) should be a good approximation to change of SAT in ice-free ocean areas; climate model simulations [Hansen et al., 2007] suggest that long-term SAT change over ice-free ocean is only slightly larger than SST change. However, ocean water temperature does not go below the freezing point of water, while surface air temperature over sea ice can be much colder. As a result, SST change underestimates SAT change when sea ice cover changes. Indeed, most climate models find that the largest SAT changes with global warming occur in regions of sea ice [IPCC, 2007]. Thus, we estimate SAT changes in sea ice regions by extrapolating actual SAT measurements on nearby land or islands; if there are no stations within 1200 km, we leave the temperature change undefined."Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2220966763638300672.post-31387789995603669312010-08-02T11:48:27.528-04:002010-08-02T11:48:27.528-04:00HR: You asked, “It looks to me like data set choi...HR: You asked, “It looks to me like data set choice would be crucial in trying to make this sort of call about the polar temperatures and maybe more importantly whats controlling them. Do you know whether NASA and CRU aknowledge this difference?”<br /><br />They understand the differences. Refer to the RealClimate post by Hansen:<br />http://www.realclimate.org/index.php/archives/2010/01/2009-temperatures-by-jim-hansen/<br />And refer to the draft of Hansen et al (2010):<br />http://data.giss.nasa.gov/gistemp/paper/gistemp2010_draft0601.pdf<br /><br />You asked, “How they justify both methods existing?”<br /><br />Hadley Centre presents the data without infilling and with minimal adjustments, while GISS elects to use the 1200km radius smoothing to infill the data. There’s no real justification needed.<br /><br />You asked, “And whether the wider polar science community has more trust in one or the other?”<br /><br />Polar researchers wouldn’t use either one. Hadley has little Arctic data, while the GISS data in most of the Arctic is make believe.Bob Tisdalehttps://www.blogger.com/profile/15462377647970214137noreply@blogger.comtag:blogger.com,1999:blog-2220966763638300672.post-73683651906585347372010-08-02T10:55:44.957-04:002010-08-02T10:55:44.957-04:00Great post. Something leaped out at me.
Fig9 show...Great post. Something leaped out at me.<br /><br />Fig9 shows a remarkable difference between GISS and HadCrut in the poles. I recently read Chylek's 2010 paper on the polar seesaw effect. When I raised some of the points highlighted in that paper with others they countered it with the Polar Amplification idea.<br /><br />One weakness in the seesaw idea for explaining the recent changes in polar temperatures has been that while Arctic temperatures have risen Anarctic temperatures haven't seen a similar fall, rather they've been fairly level in recent times. <br /><br />It looks to me like data set choice would be crucial in trying to make this sort of call about the polar temperatures and maybe more importantly whats controlling them. Do you know whether NASA and CRU aknowledge this difference? How they justify both methods existing? And whether the wider polar science community has more trust in one or the other?HRnoreply@blogger.comtag:blogger.com,1999:blog-2220966763638300672.post-49944167570227723572010-06-18T20:28:11.052-04:002010-06-18T20:28:11.052-04:00knowledgedrift (June 18, 2010 5:40 PM): Thanks fo...knowledgedrift (June 18, 2010 5:40 PM): Thanks for the pdf documenting of the SST data coordinates. They correspond with the Arctic Ocean area north of the North Atlantic, and north of Scandinavia, as illustrated in my cell c of Figure 3 from the post:<br />http://i50.tinypic.com/aensly.jpg <br /><br />GISS deletes SST data, basically, east of 40E and west of 40W.Bob Tisdalehttps://www.blogger.com/profile/15462377647970214137noreply@blogger.comtag:blogger.com,1999:blog-2220966763638300672.post-55405891210619505572010-06-18T17:40:16.998-04:002010-06-18T17:40:16.998-04:00http://knowledgedrift.files.wordpress.com/2010/06/...http://knowledgedrift.files.wordpress.com/2010/06/ocean-cells-with-data-64n-to-90n.pdf<br /><br />Couldn't figure out how to upload a spreadsheet to Wordpress, so here it is as a pdf. The grid is every 2nd latitude, hence no even numbers, that's why it starts at 65 not 64.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2220966763638300672.post-91904176140760716132010-06-18T16:48:13.716-04:002010-06-18T16:48:13.716-04:00knowledgedrift: For the SST data in the Arctic, w...knowledgedrift: For the SST data in the Arctic, what are the latitudes and longitudes of those 150 cells?Bob Tisdalehttps://www.blogger.com/profile/15462377647970214137noreply@blogger.comtag:blogger.com,1999:blog-2220966763638300672.post-59951392081456406592010-06-18T16:08:12.487-04:002010-06-18T16:08:12.487-04:00Bob,
I didn't mean to imply that you were in e...Bob,<br />I didn't mean to imply that you were in error. I was very focused on the change in ratio between land and ocean and how they handled that math. I'd have to go back and have a detailed look, but what I THINK happens is this:<br /><br />1. There are 150 ocean cells in the time series from beginning to end for that zone.<br />2. When a land cell and an ocean cell overlap, a value appears in that gridded cell that matches neither the ocean anomaly nor the land anomaly.<br />3.I did not try and reverse engineer how they arrive at the merged value. I know it is not a strict average but I only tested that on a couple of cells.<br />4.I'm not exactly certain how they depict this on the map.<br />5. When I said they don't delete it per se, that is what I meant. Ocean cells start off as just ocean cells. As more land cells appear over time, some of them coincide with the same grid points in the ocean database and they merge the data by some formula. I noticed a couple of instances where the combined data showed a zero instead, but assumed it was a fluke, most of them had data.<br /><br />I can actually pull the specific latitude and longitude for the "land only" "ocean only" and "overlap" if that helps any.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2220966763638300672.post-55920473365026364602010-06-18T15:45:39.282-04:002010-06-18T15:45:39.282-04:00knowledgedrift said, "They don't delete t...knowledgedrift said, "They don't delete the data per se, what they are doing is way worse..."<br /><br />GISS states, regarding SST data, "Areas covered occasionally by sea ice are masked using a time-independent mask.” <br /><br />This means that the data that is available is not used. In other words, they delete it. <br /><br />The 150 cells in the Arctic with SST data you mention in your post are those cells where the ocean doesn't freeze in winter, which would be north of the North Atlantic and Scandinavia. GISS deletes all SST data for the remainder of the Arctic.<br /><br />Please identify where the 150 cells with SST data are before you write that they "don't delete the data per se" and imply my post is in error.Bob Tisdalehttps://www.blogger.com/profile/15462377647970214137noreply@blogger.comtag:blogger.com,1999:blog-2220966763638300672.post-3374882497268804832010-06-18T14:05:22.837-04:002010-06-18T14:05:22.837-04:00Bob,
I downloaded the gridded anomaly data to have...Bob,<br />I downloaded the gridded anomaly data to have a more detailed look. They don't delete the data per se, what they are doing is way worse. When they combine the the land and ocean data into a single set, they make no adjustments for the increased number of land grid cells versus ocean cells.<br /><br />In 1880 64N to 90N was calculated from 212 grid cells, 150 of them ocean. In 2009 they used 722 grid cells.... 150 of them ocean. But they just total them and divide by the number of cells as if the land area actually physicaly grew!<br /><br />South zone is worse! ocean cells are 41 while land goes from 0 to 1200! They've made a .25 degree difference in the north and .75 in the south by doing the math as if the ratio in the number of data points also represented the physical ratio in size of land and ocean.<br /><br />Short version<br /><br />http://knowledgedrift.wordpress.com/2010/06/18/giss-temp-the-most-astounding-error/<br /><br />long, gory, detailed version<br /><br />http://knowledgedrift.wordpress.com/2010/06/16/giss-global-temperatures-and-math/Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2220966763638300672.post-38054916065244853672010-06-15T15:58:44.052-04:002010-06-15T15:58:44.052-04:00"I avoid land surface temperature datasets wh..."<i>I avoid land surface temperature datasets whenever possible. I wrote this post because what GISS was doing finally struck me.</i>"<br /><br />Thanks Bob,<br /><br />That point wasn't immediately clear from the post given that it was about GISS replacing SST with land surface air temperature. It just struck me as pertinent to ask why. Sorry to drag you off topic.<br /><br />NebuchadnezzarAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-2220966763638300672.post-12733827375376669662010-06-07T17:05:38.408-04:002010-06-07T17:05:38.408-04:00Anonymous: You asked, "From your comparisons...Anonymous: You asked, "From your comparisons which dataset would you consider to be most representative of the global average near surface air temperature?"<br /><br />I avoid land surface temperature datasets whenever possible. I wrote this post because what GISS was doing finally struck me.Bob Tisdalehttps://www.blogger.com/profile/15462377647970214137noreply@blogger.comtag:blogger.com,1999:blog-2220966763638300672.post-60384430775450551252010-06-07T14:36:23.647-04:002010-06-07T14:36:23.647-04:00Thanks Bob,
"Isn’t it the other way around, ...Thanks Bob,<br /><br />"Isn’t it the other way around, with NMAT mimicking SST?"<br /><br />The sea surface will affect the air above it and vice versa. I didn't want to specify any particular direction for the cause. I was simply pointing out that in an ideal world we'd use marine air temperature and SST is a reasonable substitute for that in some areas.<br /><br />"I didn’t compare models in this post. And many of the model runs used in AR4 (eleven, I believe) also model SST."<br /><br />I'm aware you don't compare to models, but I think it's worth keeping in mind as these datasets are frequently compared to models. <br /><br />The models do generally model SST - whether or not it's stored - but when the global average is computed, I believe they generally use the air temperature and this is what the observed 'global' temperature is considered to be representative of.<br /><br />From your comparisons which dataset would you consider to be most representative of the global average near surface air temperature?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-2220966763638300672.post-63932770257920820742010-06-05T18:41:59.254-04:002010-06-05T18:41:59.254-04:00Nebuchadnezzar: Thanks for the comment. You wrot...Nebuchadnezzar: Thanks for the comment. You wrote, “SST anomalies in areas of open ocean tend to track air temperature anomalies closely…”<br /><br />Isn’t it the other way around, with NMAT mimicking SST?<br /><br />You wrote, “Model estimates of global temperature typically use the modelled 2m air temperatures, so SST is not the ideal thing to compare them with.”<br /><br />I didn’t compare models in this post. And many of the model runs used in AR4 (eleven, I believe) also model SST.<br /><br />You wrote, “An additional problem is that in areas of ocean which were permanently ice covered during the climatology period it is not clear that the SST anomaly is well defined.”<br /><br />The climatology period for the SST data is 1982 to 1992, and the Reynolds OI.v2 dataset also includes Sea Ice Concentration data, which are well defined. GISS also includes the Reynolds climatology to define the areas where they mask SST data.Bob Tisdalehttps://www.blogger.com/profile/15462377647970214137noreply@blogger.comtag:blogger.com,1999:blog-2220966763638300672.post-31452026633850749112010-06-05T14:31:47.791-04:002010-06-05T14:31:47.791-04:00Hi Bob,
That's an interesting analysis and it...Hi Bob,<br /><br />That's an interesting analysis and it shows the weakness of using SST in place of air temperature over the oceans.<br /><br />Ideally, I think, the global temperature data sets would consist of air temperatures measured at a uniform height. However, air temperatures are not available in great numbers over the oceans so SST is used instead. SST anomalies in areas of open ocean tend to track air temperature anomalies closely, but this relationship breaks down near the coasts and over areas of sea ice.<br /><br />SST is therefore something of a compromise. Model estimates of global temperature typically use the modelled 2m air temperatures, so SST is not the ideal thing to compare them with.<br /><br />An additional problem is that in areas of ocean which were permanently ice covered during the climatology period it is not clear that the SST anomaly is well defined.<br /><br />NebuchadnezzarAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-2220966763638300672.post-32007091386476333882010-06-01T08:13:56.476-04:002010-06-01T08:13:56.476-04:00CoRev: But as illustrated, the bias in the Arctic...CoRev: But as illustrated, the bias in the Arctic created by deleting the SST data is not small.Bob Tisdalehttps://www.blogger.com/profile/15462377647970214137noreply@blogger.comtag:blogger.com,1999:blog-2220966763638300672.post-88487823960647512562010-06-01T07:46:26.284-04:002010-06-01T07:46:26.284-04:00Thanks for the analysis Bob. I am waiting for the...Thanks for the analysis Bob. I am waiting for the folks over at Rankexploits to finish their reviews of the current GISSTemp processing, and then the follow-on review of how those processes effect temp calculations.<br /><br />As we skeptics suspect, a very small annual bias (.001 - .0001) introduced by the processing will affect (perhaps dramatically) long range estimates.CoRevhttps://www.blogger.com/profile/04596551339753480833noreply@blogger.comtag:blogger.com,1999:blog-2220966763638300672.post-41793043371693876322010-05-31T12:31:45.077-04:002010-05-31T12:31:45.077-04:00Juraj V: Thanks for the offer on the RSS/GISTEMP ...Juraj V: Thanks for the offer on the RSS/GISTEMP comparison, but I've got to get back to my long-term project and a video I've been working on. <br /><br />RegardsBob Tisdalehttps://www.blogger.com/profile/15462377647970214137noreply@blogger.comtag:blogger.com,1999:blog-2220966763638300672.post-23947437561230000592010-05-31T11:47:17.495-04:002010-05-31T11:47:17.495-04:00Excellent stuff. The divergence is quite big alrea...Excellent stuff. The divergence is quite big already, so even the polar areas are not that big, they do count.<br />http://www.woodfortrees.org/plot/gistemp/from:1998/plot/hadcrut3vgl/from:1998<br /><br />I have started comparison of HadCRUT/MSU trends since 1979 in 60x30° grids accross the whole globe, like you did RSS vs GISTEMP. If you are interested in results, just e-mail me.<br />Juraj V.Unknownhttps://www.blogger.com/profile/01284441733104541252noreply@blogger.com