Comments on: GISTEMP Urban Adjustment http://clearclimatecode.org/gistemp-urban-adjustment/ Sat, 04 Sep 2010 02:39:50 +0000 http://wordpress.org/?v=2.9.2 hourly 1 By: Zeke Hausfather http://clearclimatecode.org/gistemp-urban-adjustment/comment-page-1/#comment-2706 Zeke Hausfather Fri, 09 Jul 2010 20:25:15 +0000 http://clearclimatecode.org/?p=209#comment-2706 Nick, Ahh, thats what I get for reading too quickly :-P Nick,

Ahh, thats what I get for reading too quickly :-P

]]> By: Nick.Barnes http://clearclimatecode.org/gistemp-urban-adjustment/comment-page-1/#comment-2633 Nick.Barnes Fri, 02 Jul 2010 14:55:44 +0000 http://clearclimatecode.org/?p=209#comment-2633 Zeke: the graphs above are land-only. Zeke: the graphs above are land-only.

]]> By: Zeke Hausfather http://clearclimatecode.org/gistemp-urban-adjustment/comment-page-1/#comment-2632 Zeke Hausfather Fri, 02 Jul 2010 14:26:05 +0000 http://clearclimatecode.org/?p=209#comment-2632 Mike Edwards, In general, SST tends to dominate any global reconstruction. A plot of land-only unadjusted and UHI-adjusted GISTemp data would show a more discernible difference (but still not huge). Mike Edwards,

In general, SST tends to dominate any global reconstruction. A plot of land-only unadjusted and UHI-adjusted GISTemp data would show a more discernible difference (but still not huge).

]]> By: Nick.Barnes http://clearclimatecode.org/gistemp-urban-adjustment/comment-page-1/#comment-2592 Nick.Barnes Tue, 29 Jun 2010 22:20:29 +0000 http://clearclimatecode.org/?p=209#comment-2592 @Mike Edwards: Do you understand how the UHI adjustment works in GISTEMP? Do you have any suggestions for improving it? @Mike Edwards: Do you understand how the UHI adjustment works in GISTEMP? Do you have any suggestions for improving it?

]]> By: Mike Edwards http://clearclimatecode.org/gistemp-urban-adjustment/comment-page-1/#comment-2590 Mike Edwards Tue, 29 Jun 2010 21:48:36 +0000 http://clearclimatecode.org/?p=209#comment-2590 @Nick Barnes While I can accept that much of the world's surface isn't urban (it's mostly ocean!), I am puzzled by your statement that "although quite a few of the weather stations qualify as urban...the UHI effect at those stations is not enormous" From the studies I've seen of UHI effects, I would expect the UHI to be substantial enough to show up in the adjustments - if that isn't the case, then I doubt that the adjustments are doing thier job, given the studies I've seen on the magnitude of the UHI effect. @Nick Barnes

While I can accept that much of the world’s surface isn’t urban (it’s mostly ocean!), I am puzzled by your statement that “although quite a few of the weather stations qualify as urban…the UHI effect at those stations is not enormous”

From the studies I’ve seen of UHI effects, I would expect the UHI to be substantial enough to show up in the adjustments – if that isn’t the case, then I doubt that the adjustments are doing thier job, given the studies I’ve seen on the magnitude of the UHI effect.

]]> By: Nick.Barnes http://clearclimatecode.org/gistemp-urban-adjustment/comment-page-1/#comment-2585 Nick.Barnes Tue, 29 Jun 2010 12:31:53 +0000 http://clearclimatecode.org/?p=209#comment-2585 @Mike Edwards: There are lots of studies - hundreds, at least - of the urban heat island effect, and quite a lot of effort has gone into identifying, quantifying, modelling, and adjusting for the effect of UHI on global temperature records. For GISTEMP, you can see, for instance, section 5 of <a href="http://pubs.giss.nasa.gov/cgi-bin/abstract.cgi?id=ha03200f" rel="nofollow">Hansen et al 1999</a>, or section 3.1 of <a href="http://data.giss.nasa.gov/gistemp/paper/gistemp2010_draft0601.pdf" rel="nofollow">the draft Hansen et al 2010</a>. These sections look at example station records, as well as the net effect. If you are interested in the effect at particular stations, you can go to <a href="http://data.giss.nasa.gov/gistemp/station_data/" rel="nofollow">the GISTEMP station data page</a> and see station records before and after UHI adjustment. If you want better or more detailed analysis, you can easily download <a href="http://code.google.com/p/ccc-gistemp/" rel="nofollow">ccc-gistemp</a> and fiddle with <a href="http://code.google.com/p/ccc-gistemp/source/browse/trunk/code/step2.py" rel="nofollow">step2.py</a> yourself. For instance, it is easy to change the code which discriminates between urban and rural stations, or to add code to log the adjustments made. We want to write better visualisations ourselves, but haven't done so yet. "Isn't it more than a little curious": No, I don't think so. I think it is exactly "a little curious": it is a surprising result at first glance, but when one analyses it in more detail the surprise diminishes. Very little of the world's surface is urban, and although quite a few of the weather stations qualify as urban, it turns out that the urban heat island effect at those stations, while measurable, is not enormous. @Mike Edwards: There are lots of studies – hundreds, at least – of the urban heat island effect, and quite a lot of effort has gone into identifying, quantifying, modelling, and adjusting for the effect of UHI on global temperature records. For GISTEMP, you can see, for instance, section 5 of Hansen et al 1999, or section 3.1 of the draft Hansen et al 2010. These sections look at example station records, as well as the net effect.

If you are interested in the effect at particular stations, you can go to the GISTEMP station data page and see station records before and after UHI adjustment. If you want better or more detailed analysis, you can easily download ccc-gistemp and fiddle with step2.py yourself. For instance, it is easy to change the code which discriminates between urban and rural stations, or to add code to log the adjustments made. We want to write better visualisations ourselves, but haven’t done so yet.

“Isn’t it more than a little curious”: No, I don’t think so. I think it is exactly “a little curious”: it is a surprising result at first glance, but when one analyses it in more detail the surprise diminishes. Very little of the world’s surface is urban, and although quite a few of the weather stations qualify as urban, it turns out that the urban heat island effect at those stations, while measurable, is not enormous.

]]> By: Mike Edwards http://clearclimatecode.org/gistemp-urban-adjustment/comment-page-1/#comment-2582 Mike Edwards Tue, 29 Jun 2010 06:42:28 +0000 http://clearclimatecode.org/?p=209#comment-2582 Folks, Isn't it more than a little curious that an adjustment supposedly made to deal with the effects of UHI actually has no discernable effect on the outcome of the calculations? What are the possible explanations for this? o UHI does not exist. A little unlikely given the previous studies I've seen. o Very few of the stations used in these calculations are subject to UHI. Also seems unlikely from my knowledge of some of the stations used, although it is worth acknowledging that 70% of the Earth's surface is ocean. o The adjustment for UHI is a failure. ie UHI effects are not actually removed by the adjustment procedure. Are there any studies of the effects of the procedure on stations which might be expected to suffer from UHI? Folks,

Isn’t it more than a little curious that an adjustment supposedly made to deal with the effects of UHI actually has no discernable effect on the outcome of the calculations?

What are the possible explanations for this?

o UHI does not exist. A little unlikely given the previous studies I’ve seen.

o Very few of the stations used in these calculations are subject to UHI. Also seems unlikely from my knowledge of some of the stations used, although it is worth acknowledging that 70% of the Earth’s surface is ocean.

o The adjustment for UHI is a failure. ie UHI effects are not actually removed by the adjustment procedure.

Are there any studies of the effects of the procedure on stations which might be expected to suffer from UHI?

]]> By: The Blackboard » Replication http://clearclimatecode.org/gistemp-urban-adjustment/comment-page-1/#comment-2539 The Blackboard » Replication Fri, 25 Jun 2010 18:33:41 +0000 http://clearclimatecode.org/?p=209#comment-2539 [...] The image at the start of the post presents a replication of GISTemp using either GHCN raw or GISS land temp data coupled with HadISST1/Reynolds ocean data and the effects of interpolation. The latter factor is estimated by taking the difference between standard GISTemp values and those from a version of GISTemp run for only areas covered by HadCRUT, which effectively filters out the net effect of 1200 km interpolation. Its worth noting that the difference between using GISS Step 0 and GHCN raw land data is fairly negligible, despite the fact that GISS Step 0 presumably uses adjusted (rather than raw) USHCN data as well as Antarctic station data. Similarly, its notable that the GISS urban adjustments (via nightlights) don’t appear to have a large impact vis-a-vis the unadjusted data, a point that others have previously made. [...] [...] The image at the start of the post presents a replication of GISTemp using either GHCN raw or GISS land temp data coupled with HadISST1/Reynolds ocean data and the effects of interpolation. The latter factor is estimated by taking the difference between standard GISTemp values and those from a version of GISTemp run for only areas covered by HadCRUT, which effectively filters out the net effect of 1200 km interpolation. Its worth noting that the difference between using GISS Step 0 and GHCN raw land data is fairly negligible, despite the fact that GISS Step 0 presumably uses adjusted (rather than raw) USHCN data as well as Antarctic station data. Similarly, its notable that the GISS urban adjustments (via nightlights) don’t appear to have a large impact vis-a-vis the unadjusted data, a point that others have previously made. [...]

]]> By: steven mosher http://clearclimatecode.org/gistemp-urban-adjustment/comment-page-1/#comment-731 steven mosher Sat, 27 Mar 2010 07:13:39 +0000 http://clearclimatecode.org/?p=209#comment-731 Hi Nick, Check out this guy http://oneillp.wordpress.com/2010/03/23/ghcn-metadata-v2-inv-gistemp-and-night-light-radiance/#comment-19 He's got some GISS questions ( data questions upstream of you ) and I thought he might use your good graces with Dr. Rudy to maybe get some answers. Hi Nick,

Check out this guy

http://oneillp.wordpress.com/2010/03/23/ghcn-metadata-v2-inv-gistemp-and-night-light-radiance/#comment-19

He’s got some GISS questions ( data questions upstream of you )
and I thought he might use your good graces with Dr. Rudy to
maybe get some answers.

]]> By: Nick.Barnes http://clearclimatecode.org/gistemp-urban-adjustment/comment-page-1/#comment-365 Nick.Barnes Tue, 09 Mar 2010 08:55:35 +0000 http://clearclimatecode.org/?p=209#comment-365 I took out the step 2 logging because maintaining exact logging compatibility with GISTEMP was a pain: for instance, we were having to construct and pass around special "station descriptor" strings - composed of the station name, part of the station ID, and bits and pieces of metadata - specifically to write them out in log files. To visualise and debug step 2 processes, some sort of logging may be useful (although I think for visualisation I would prefer for the information to be added to metadata, for instance the list of rural station IDs used to adjust an urban station record should be a metadata item for the urban station). But it should be a logging format which makes sense for the new code. I took out the step 2 logging because maintaining exact logging compatibility with GISTEMP was a pain: for instance, we were having to construct and pass around special “station descriptor” strings – composed of the station name, part of the station ID, and bits and pieces of metadata – specifically to write them out in log files.
To visualise and debug step 2 processes, some sort of logging may be useful (although I think for visualisation I would prefer for the information to be added to metadata, for instance the list of rural station IDs used to adjust an urban station record should be a metadata item for the urban station). But it should be a logging format which makes sense for the new code.

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