tag:blogger.com,1999:blog-9093436161326155359.post6107639086203980758..comments2024-03-28T06:43:02.954+00:00Comments on Variable Variability: Temperature trend over last 15 years is twice as large as previously thoughtVictor Venemahttp://www.blogger.com/profile/02842816166712285801noreply@blogger.comBlogger15125tag:blogger.com,1999:blog-9093436161326155359.post-69529211970141301002013-11-22T00:33:54.997+00:002013-11-22T00:33:54.997+00:00Carl Mears, thank you very much for your assessmen...Carl Mears, thank you very much for your assessment. I had expected that the quality of the satellite datasets would be the main problem. In fact without the careful cross-validation I would have been very skeptical of this C&W study because of the satellite data.<br /><br />So your assessment makes the C&W paper more convincing.Victor Venemahttps://www.blogger.com/profile/02842816166712285801noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-46011563247073554432013-11-21T18:04:31.018+00:002013-11-21T18:04:31.018+00:00Hi
You say:
"Maybe it would be better to a...Hi <br /><br />You say: <br />"Maybe it would be better to ask the mainstream scientists behind the <br />RSS dataset. They are the ones that did not trust the data sufficiently <br />and rather leave a gap in the Arctic."<br /><br />OK, I'll bite. <br /><br />First, the gap in the arctic is relatively small, only for 82.5N to <br />the pole. If you look at a polar projection, you can see that this <br />is quite a small area. The reason we leave out this area is <br />because the part of the satellite data we use *does not view* <br />this area. The UAH team interpolates the data to fill in the <br />hole at the pole.<br /><br />The south pole is more complicated. We view the TLT product <br />as a atmospheric temperature product. For areas with low <br />surface elevations, this is true, with ~90% of the signal <br />coming from atmospheric emission. For regions with high <br />surface elevations, the portion that comes from the atmosphere <br />is reduced, because the atmosphere is thinner, and thus <br />more transparent. Much of the Antarctic continent is above <br />2000m, so the portion of the signal that comes from the <br />atmosphere is sharply reduced, to as low as 60%. So TLT <br />is no longer an atmospheric product. <br /><br />There is a second problem as well. To calculate the TLT <br />product, we use a method developed by the UAH group, <br />where we calculate the weighted difference between satellite <br />measurements at different viewing angles AND at <br />different locations. When some of the views are on the <br />Antarctic continent, and some are in the surrounding <br />ocean, there is a large spatial gradient <br />in the measurements that pollutes the TLT retrieval <br />(which is based on vertical gradients). Away from <br />the poles, this problem averages out when we make monthly <br />mean maps, but doesn't do so near the poles for geometric <br />reasons. You can look in Mears and Wentz, 2009 http://images.remss.com/papers/rsspubs/Mears_JTECH_2009_TLT_construction.pdf <br />for more details.<br /><br />These problems lead us to not provide TLT data south of 70S. <br />But I don't think is matters much for the paper under <br />discussion because:<br />1. Most of the effect is from the Arctic. <br />2. The data is used in Cowtan and Way to provide a spatial <br />pattern to fill in the surface temperatures. I don't think <br />it matters that the UAH TLT product is not really an <br />atmospheric temperature over Antarctica -- in fact, for <br />this application, some surface emission in the data product <br />is probably a good thing, since it is the surface <br />temperature that we are interested in.Carl Mearshttps://www.blogger.com/profile/12226449864107329314noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-73457978403889358572013-11-15T10:41:18.325+00:002013-11-15T10:41:18.325+00:00One of the interesting things of blogging is every...One of the interesting things of blogging is everything that happens in the background. A colleague has asked Stephen Outten to send me some papers on the relation between Arctic sea ice and temperature.<br /><br />Stephen Outten send me these two recent articles.<br /><br />Outten, S., R. Davy, and I. Esau, 2013: Eurasian winter cooling: Intercomparison of reanalyses and CMIP5 data sets, Atmos. Oceanic Sci. Lett., 6, 324‒331, doi: <a href="10.3878/j.issn.1674-2834.12.0112" rel="nofollow">10.3878/j.issn.1674-2834.12.0112</a>.<br /><br />Outten, S. D., I. Esau. A link between Arctic sea ice and recent cooling trends over Eurasia. Climatic Change, February 2012, Volume 110, Issue 3-4, pp 1069-1075doi: <a href="10.1007/s10584-011-0334-z" rel="nofollow">10.1007/s10584-011-0334-z</a>.Victor Venemahttps://www.blogger.com/profile/02842816166712285801noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-58274969167504950982013-11-15T01:07:19.113+00:002013-11-15T01:07:19.113+00:00Victor, re the dramatic change I should better hav...Victor, re the dramatic change I should better have said that this is what I would expect to see in the GCMs. They would certainly get the WACCY (Warm Arctic Cold Continent) pattern right if only they were informed about the observed sea ice conditions a priori. As you rightly said, Kosaka & Xie for the Arctic. To my knowledge, there isn't too much in the literature yet. Hope that people are working on that. Some examples which point in the right direction:<br /><br />Orsolini et al. 2012 (doi:10.1007/s00382-011-1169-z)<br />Petoukhov and Semenov 2010 (doi:10.1029/2009JD013568)<br />Screen et al. 2013 (doi:http://dx.doi.org/10.1175/JCLI-D-12-00063.1)<br />Jun et al. 2013 (doi:10.1007/s00382-013-1897-3)<br /><br />Earlier commentary and linklist from ECCO2 project:<br /><br />Greene and Monger, 2012 (doi:http://dx.doi.org/10.5670/oceanog.2012.58)<br />http://ecco2.org/manuscripts/<br /><br />I agree, if the Arctic amplification turns out to have an even stronger impact on the global temperature (as suggested by Cowtan and Way), we wouldn't need to be too worried about the apparant (temporary) negative winter feedback in Eurasia due to negative AO. Masking Eurasia in winter leads to this (using the current HadCRUT4 version): <a href="http://3.bp.blogspot.com/-R7LejLY07FM/UjckZkLsR4I/AAAAAAAAAKU/t8748_Xw6z4/s1600/s1.jpg" rel="nofollow">HadCRUT4 masked</a> (credit to <a href="http://klimazwiebel.blogspot.co.uk/2013/09/the-intriguing-stagnation.html" rel="nofollow">Eduardo</a>)<br /><br />No hiatus whatsoever! However, take Cowtan and Way's complete HadCRUT4 version and leave Eurasia as is, the global average will be lower than masking both, Eurasia and the Arctic. My point is, I still think we see a slight negative AO related global temperature impact. Interestingly, if AO is strongly positive as it is the case right now, Eurasia sends the global temperature anomaly to record level. Wouldn't be surprised if Nov will be the warmest ever (we will know in a week from now).<br /><br />On top of it all, the (negative) ENSO trend remains to be another important issue. Nothing has changed in that regard! What Cowtan and Way shows is that there is a potential for an even stronger surface temperature trend than previously thought.K.a.r.S.t.e.Nhttp://www.karstenhaustein.com/climatenoreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-3242637020007143952013-11-14T18:27:32.137+00:002013-11-14T18:27:32.137+00:00K.a.r.S.t.e.N, thanks for your nice words.
Do I u...K.a.r.S.t.e.N, thanks for your nice words.<br /><br />Do I understand you right that the dramatic change, when forcing with observed sea ice, is that the modelled temperatures then match the observed ones very well?<br /><br />A kind of Kosaka & Xie study, but not for the pacific, but for the Arctic. That is interesting. Do you happen to have a link to that? That could be interesting for some readers.<br /><br />That would conclude that there is no problem with the theory of global warming, which was anyway a strange idea, or with the climate models in general, which could have been more to the point, but that we do have a problem with the modelling of Arctic sea ice in global models. Right?Victor Venemahttps://www.blogger.com/profile/02842816166712285801noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-13939960773342281162013-11-14T18:14:10.541+00:002013-11-14T18:14:10.541+00:00Victor, thanks for putting all this together and f...Victor, thanks for putting all this together and for sharing your wisdom. Very much appreciated! Re Kosaka & Xie, I think it is interesting to note that their "tweaked" simulation (i.e. driven with observed Pacific SSTs = their POGA-H experiment) does not only have trouble to get the observed Eurasian sfc temperature trend right, but also the Arctic Amplification. It would therefore be great to see how it compares with the extended HadCRUT4 dataset rather than the current incomplete version given that POGA-H runs still a bit warmer than the original HadCRUT4 data. Should result either in a perfect match or a slight underestimation of the trend as far as the model is concerned.<br /><br />While the Arctic Amplification is reproduced in the GCMs in general, they fail to get the observed magnitude right by quite a wide margin. Force them with observed sea ice extent and things will change dramatically. What I'm saying is that masking the GCMs in the way Ed did it, won't make it an apples to apples comparion as long as the GCMs keep producing very warm winter sfc temperatures over Eurasia. My guess regarding Ed's plot would be that the model trend will increase only slightly, while the HadCRUT4 trend will increase significantly. Might well fall in the 25-75% range of the CMIP5 ensemble after the correction. I'm sure we're gonna see an update soon ... keeping always in mind that Cowtan and Way is certainly not gonna be the last word.K.a.r.S.t.e.Nhttp://www.karstenhaustein.com/climatenoreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-14008055148341921562013-11-14T16:06:27.625+00:002013-11-14T16:06:27.625+00:00Peter, thanks for the warning. I have removed the ...Peter, thanks for the warning. I have removed the link to the free manuscript from the post. Should have looked better what I was linking to.<br /><br />The Arctic gap will be much less important for the long term trend. That is likely something special for the recent past in which we also saw a huge decline in Arctic sea ice. And maybe it would change some other decades by a similar minor amount.<br /><br />Some comments on other blogs are really weird and make a crisis in climatology out of it. Some act as if they do not understand that two times almost nothing is still almost nothing and that this study makes a minute change to the centennial temperature signal. Maybe the cognitive dissonance of acting as if this almost nothing is an argument in their political battle.Victor Venemahttps://www.blogger.com/profile/02842816166712285801noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-39717614471494173892013-11-14T15:31:06.300+00:002013-11-14T15:31:06.300+00:00Just to clarify the paper I linked to is the HadCR...Just to clarify the paper I linked to is the HadCRUT4 paper not the new analysis. Like everyone else its ask for a pre-print or find the fee down the back of the sofa. I took option #1. Sorry for any confusion. Its a really neat analysis.<br /><br />Its also worth noting that the opposite study - calculating for common geospatial coverage - was done by Vose et al in 2005 and found remarkable similarity. Since then UK and US SST and land analyses have developed respectively. It would be interesting to redo that now looking at what portion of diffs arises from data analysis in areas of common analysis and what portion arises from unique data / interpolation.PeterThornehttps://www.blogger.com/profile/02438826461353615177noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-10340675216724456912013-11-14T10:43:07.011+00:002013-11-14T10:43:07.011+00:00Interesting post Victor. Thank you.
As for Daneel...Interesting post Victor. Thank you.<br /><br />As for Daneel's question, this may help<br /><br />This is Ed Hawkins blog post on *that* comparison of models and global temp.<br /><br />"A recent comparison of global temperature observations and model simulations on this blog prompted a rush of media and wider interest, notably in the Daily Mail, The Economist & in evidence to the US House of Representatives. Given the widespread misinterpretation of this comparison, often without the correct attribution or links to the original source, a more complete description & update is needed.<br /><br />"Also note that I have ‘masked’ the simulations to only use data at the same locations where gridded observations in the HadCRUT4 dataset exist."<br /><br />http://www.climate-lab-book.ac.uk/2013/comparing-observations-and-simulations-again/MikeHnoreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-44103729474248996892013-11-14T09:04:16.080+00:002013-11-14T09:04:16.080+00:00A few brief observations:
1. This issue of sampli...A few brief observations:<br /><br />1. This issue of sampling isn't entirely new or uninvestigated. See <a href="http://www.metoffice.gov.uk/news/releases/archive/2009/land-warming-record" rel="nofollow">here</a> for example.<br /><br />2. GISS and NCDC MLOST do interpolate over some distance from real observations. Even HadCRUT gridding to 5 degree is arguably a form of limited interpolation. But interpolation is a vexed issue. We certainly need to do better on producing globally complete estimates and their uncertainties. And it certainly impacts on trends, particularly shorter-term trends.<br /><br />3. HadCRUT does account for spatial incompleteness. It does this through its error model rather than attempting to interpolate. So, if you use and propogate the uncertainty estimates appropriately you will find that HadCRUT's estimates are consistent with a higher warming rate than its median estimator. Probably higher than even this estimate. See some pretty pictures at <a href="http://www.metoffice.gov.uk/hadobs/hadcrut4/diagrams.html" rel="nofollow">here</a> or read the whole <a href="http://www.metoffice.gov.uk/hadobs/hadcrut4/HadCRUT4_accepted.pdf" rel="nofollow">paper</a> here.PeterThornehttps://www.blogger.com/profile/02438826461353615177noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-1272788891681500442013-11-13T22:55:44.602+00:002013-11-13T22:55:44.602+00:00R. Daneel, at Planet 3.0 Stefan Rahmstorf has resp...R. Daneel, at Planet 3.0 Stefan Rahmstorf has responded by mail to your question:<br /><br /><a href="http://planet3.org/2013/11/13/thie-disappearing-hiatus/#comment-52493" rel="nofollow">Rahmstorf via email</a>:<br /><i>“Not all explanation of the slowdown are additional – like ocean heat storage is the mechanism by which ENSO influences global mean temperature, not an additional thing.<br /><br />The radiative forcing discussion is highly speculative due to lack of sufficiently accurate data to nail down significant deviations in the net radiative forcing over such a short time period.<br /><br />And if after all adjustments the global warming trend shows some acceleration, this would probably get the data closer to the model-mean (rather than to a continued linear warming trend).<br /><br />But it would probably not be statistically significant, so interpreting an acceleration into 15 years of data would be as ill-founded as finding a slowdown.</i>Victor Venemahttps://www.blogger.com/profile/02842816166712285801noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-54798001206651925682013-11-13T21:40:09.684+00:002013-11-13T21:40:09.684+00:00The main reason it has not been done before is tha...The main reason it has not been done before is that it is quite complicated and it will require much further research to show that the method works reliably. This paper mainly shows that such research would be worthwhile.<br /><br />Another reason is that you can only do this for the satellite period. Which is rather short and thus not very interesting climatologically.<br /><br />Finally, a reason is likely that the "hiatus" is minor and that scientists thus likely not found it to be very interesting and maybe also did not expect that it would be possible to study something that small.<br /><br />You can only get funding for scientifically interesting problems. The nonsense hypes of WUWT and Co. are not taken into account by the science funding agencies. The authors of this paper did the study in their free time.<br /><br />The gap is filled with normal interpolation in the GISS dataset. This dataset also has a somewhat higher trend for the last 15 years. And according to Rahmstorf at RealClimate the GISS dataset has still some problems with ocean temperatures. If this problem is corrected the trend in the GISS dataset over the last 15 years would be 0.1°C per decade. Quite similar.Victor Venemahttps://www.blogger.com/profile/02842816166712285801noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-54684616616876912542013-11-13T21:22:32.068+00:002013-11-13T21:22:32.068+00:00This filling in the gaps of the temperature record...This filling in the gaps of the temperature record seems like a logical thing to do. I can't help but wonder why no-one has done it before. <br /><br />What is a little frustrating/amusing is that we seem to have gone from explaining the hiatus in terms of aerosols/natural variation/ocean heat uptake to now there is no hiatus. Probably in reality it's a bit of both but I can't help but feel a little bit silly given that I've been arguing something that's not entirely true. But as you say, it's early days yet and things may change. It's science after all. Rachelhttps://www.blogger.com/profile/09129841408329015509noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-5818582074800192002013-11-13T19:56:10.150+00:002013-11-13T19:56:10.150+00:00Hello R Daneel, that was also the first question t...Hello R Daneel, that was also the first question that I was thinking of. That is why I would like to wait some time until the dust settles.<br /><br />I am not a modeller, but I think I have seen people use a global mean temperature based on the model values at the locations of the climate stations. I have no idea, however, how often that is used. <br /><br />Also for the validation of weather predicting such an approach is often used for more difficult parameters (for example radar precipitation measurements). And people have started simulating some paleo proxies in climate models.<br /><br />Because the correlation of the global mean temperature in Kosaka & Xie was so high, I can imagine that they used such an approach. <br /><br />I am not sure whether there would be a problem. The changes are very small. Kevin Cowtan and Robert G. Way, for example, explicitly write on <a href="http://www-users.york.ac.uk/~kdc3/papers/coverage2013/" rel="nofollow">their background homepage</a>, that their better interpolated data is still within the error margins of the HadCRUT data.Victor Venemahttps://www.blogger.com/profile/02842816166712285801noreply@blogger.comtag:blogger.com,1999:blog-9093436161326155359.post-19350385808763040752013-11-13T19:37:02.687+00:002013-11-13T19:37:02.687+00:00It's a nice reminder that every time you start...It's a nice reminder that every time you start looking for an explanation, you first need to be sure that there's an effect in need of one. <br /><br />I'm curious to see how this research fits into other studies about the "pause" (AKA, "the paws"). Seems that Kosaka & Xie 2013 might be at odds with this finding since their POGA-H model had an excellent fit with the original temperature record. <br /><br />That brings me to a question. When a model is compared with a temperature record, ¿do they use the same averaging method? It seems to me that if you are using an average observed temperature that doesn't include the Arctic, then you should construct an average model temperature with exactly the same coverage. I don't know if that's customary but if that's what K&X did then there would be no problem. Anonymoushttps://www.blogger.com/profile/07982409667756307764noreply@blogger.com