Comments on: Surface Temperatures – How significant is the January 2008 fall? http://landshape.org/enm/surface-temperatures/ The Power of Numeracy Tue, 07 Feb 2012 17:57:00 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: Niche Modeling » Rahmstorf 7 Finale http://landshape.org/enm/surface-temperatures/#comment-5980 Niche Modeling » Rahmstorf 7 Finale Wed, 23 Apr 2008 03:25:26 +0000 http://landshape.org/enm/surface-temperatures/#comment-5980 [...] This paper claimed to show that: The data available for the period since 1990 raise concerns that the climate system, in particular sea level, may be responding more quickly to climate change than our current generation of models indicates. By way of recap, this paper figured prominently in the Interim Report of the Garnaut Review where it is clearly used as a source of mainstream scientific opinion: “Developments in mainstream scientific opinion on the relationship between emissions, accumulations and climate outcomes, and the Review’s own work on future business-as-usual global emissions, suggest that the world is moving towards high risks of dangerous climate change more rapidly than has generally been understood.” Interest in the current weather has been growing since people have been observing either sharp declines in temperatures since last year, or relative stability in temperatures over about the last 10 years and wondering how these fit into the picture of global warming. I did some posts putting it into context showing last years temperature drop was not unusual here, that a particular 10 year period has been flat here, and that a number of climate indicators are showing decadal stability here. The Blackboard has been spear-heading rigorous statistical methods for checking IPCC projections and finding post 2001 TAR consistently falsified by climate trends. Contradicting these findings was the paper by Rahmstorf et al 2007, published in Science, by seven of the leading members of the IPCC scientific team. So, I started to audit this paper to see if this paper does in fact provide a more reliable perspective on the issue of whether climate is changing faster or slower than expected. A number of bloggers ‘raised concerns’ about the vague description of the methodology, and argued at Niche Modeling and The Blackboard that there were important sources of uncertainty unaccounted for. Other blogs picked up the issue including Peter Gallagher and Mark Lawson. Stefan Rahmstorf and I exchanged comments at RealClimate.org and here. His main defense was that the end point uncertainty would only affect the last 5 points of the smoothed trend line with an 11 point embedding. Here the global temperatures were smoothed using a complex method called Singular Spectrum Analysis (SSA). I gave examples of SSA and other methods where the end point uncertainty affected virtually ALL points in the smoothed trend line, and particularly more than 5 end points. Stefan clearly had little idea of how SSA worked. His final message, without an argument, was: [Response: If you really think you’d come to a different conclusion with a different analysis method, I suggest you submit it to a journal, like we did. I am unconvinced, though. -stefan] So much for the recap. Keep in mind that the purpose of a scientific exchange like this is to clarify the points of agreement and disagreement and attempt to arrive at a resolution on the validity of the claims. Note the problem I raised is not the only obvious problem either, but just one I worked on. This is not meant to be a personal process. I am grateful for someone to point out errors in my work and would try to understand them, as I would rather not be blowing smoke unintentionally. This example highlights the power of numbers to resolve an issue. Stefan can have his opinion, and I have opinions too, but the thing I love is the power of numbers to arbitrate and discriminate, and ultimately eliminate the unjustified ones. Also I was wanting to address the Garnaut Review, as I feel that they are abrogating a duty of diligence by not paying more critical attention to papers such as these. Here was an opportunity to give a specific example of a paper with flaws so obvious that it SHOULD have been dismissed by anyone with statistical training, or background knowledge. So thank you readers for your patience with this process. I have put a submission into the Garnaut Review supported by documentation from the web sites involved. Here is a good example of the use of blogs. As the time for comments has closed, I could not submit a critique to Science. It is also better to have a through and open discussion of the issues at hand anyway, before rushing to publication of critical comments, so both can gain a deeper understanding of the finer points. It is unfortunate that Stefan cut the discussion off, but to his credit he was responsive to the actual concerns in the replies he did make. [...] [...] This paper claimed to show that: The data available for the period since 1990 raise concerns that the climate system, in particular sea level, may be responding more quickly to climate change than our current generation of models indicates. By way of recap, this paper figured prominently in the Interim Report of the Garnaut Review where it is clearly used as a source of mainstream scientific opinion: “Developments in mainstream scientific opinion on the relationship between emissions, accumulations and climate outcomes, and the Review’s own work on future business-as-usual global emissions, suggest that the world is moving towards high risks of dangerous climate change more rapidly than has generally been understood.” Interest in the current weather has been growing since people have been observing either sharp declines in temperatures since last year, or relative stability in temperatures over about the last 10 years and wondering how these fit into the picture of global warming. I did some posts putting it into context showing last years temperature drop was not unusual here, that a particular 10 year period has been flat here, and that a number of climate indicators are showing decadal stability here. The Blackboard has been spear-heading rigorous statistical methods for checking IPCC projections and finding post 2001 TAR consistently falsified by climate trends. Contradicting these findings was the paper by Rahmstorf et al 2007, published in Science, by seven of the leading members of the IPCC scientific team. So, I started to audit this paper to see if this paper does in fact provide a more reliable perspective on the issue of whether climate is changing faster or slower than expected. A number of bloggers ‘raised concerns’ about the vague description of the methodology, and argued at Niche Modeling and The Blackboard that there were important sources of uncertainty unaccounted for. Other blogs picked up the issue including Peter Gallagher and Mark Lawson. Stefan Rahmstorf and I exchanged comments at RealClimate.org and here. His main defense was that the end point uncertainty would only affect the last 5 points of the smoothed trend line with an 11 point embedding. Here the global temperatures were smoothed using a complex method called Singular Spectrum Analysis (SSA). I gave examples of SSA and other methods where the end point uncertainty affected virtually ALL points in the smoothed trend line, and particularly more than 5 end points. Stefan clearly had little idea of how SSA worked. His final message, without an argument, was: [Response: If you really think you’d come to a different conclusion with a different analysis method, I suggest you submit it to a journal, like we did. I am unconvinced, though. -stefan] So much for the recap. Keep in mind that the purpose of a scientific exchange like this is to clarify the points of agreement and disagreement and attempt to arrive at a resolution on the validity of the claims. Note the problem I raised is not the only obvious problem either, but just one I worked on. This is not meant to be a personal process. I am grateful for someone to point out errors in my work and would try to understand them, as I would rather not be blowing smoke unintentionally. This example highlights the power of numbers to resolve an issue. Stefan can have his opinion, and I have opinions too, but the thing I love is the power of numbers to arbitrate and discriminate, and ultimately eliminate the unjustified ones. Also I was wanting to address the Garnaut Review, as I feel that they are abrogating a duty of diligence by not paying more critical attention to papers such as these. Here was an opportunity to give a specific example of a paper with flaws so obvious that it SHOULD have been dismissed by anyone with statistical training, or background knowledge. So thank you readers for your patience with this process. I have put a submission into the Garnaut Review supported by documentation from the web sites involved. Here is a good example of the use of blogs. As the time for comments has closed, I could not submit a critique to Science. It is also better to have a through and open discussion of the issues at hand anyway, before rushing to publication of critical comments, so both can gain a deeper understanding of the finer points. It is unfortunate that Stefan cut the discussion off, but to his credit he was responsive to the actual concerns in the replies he did make. [...]

]]> By: Niche Modeling » March Global Temperatures 2008 http://landshape.org/enm/surface-temperatures/#comment-5979 Niche Modeling » March Global Temperatures 2008 Tue, 18 Mar 2008 20:45:39 +0000 http://landshape.org/enm/surface-temperatures/#comment-5979 [...] However, the big change in the UAH this month was in the southern hemisphere, continuing to decline to -0.21C from 0.02C the previous month. Update: RSS reports a global increase of +0.06C and southern hemisphere change of -0.12C. It will be interesting to see what happens to global temperatures in March 2008. In past years, downswings in temperatures have rapidly rebounded to higher levels. There is some evidence that this downswing corresponds with a discrete change in ocean circulation, in which case we may not see a rebound this time. Here are the links to the data sets. OrganizationNameURL Remote Sensing SystemsRSSftp://ftp.ssmi.com/msu/monthly_time_series/rss_monthly_msu_amsu_channel_tlt_anomalies_land_and_ocean_v03_1.txt Uni. Alabama HuntsvilleUAHhttp://vortex.nsstc.uah.edu/public/msu/t2lt/tltglhmam_5.2 NASAGISShttp://data.giss.nasa.gov/gistemp/tabledata/GLB.Ts+dSST.txt Hadley CenterCRUhttp://hadobs.metoffice.com/hadcrut3/diagnostics/global/nh+sh/monthly Predictably, there has also been much side-talk on the blogs about ‘a single year does not a trend make’. For the record, I did an analysis here which showed that when the non-normality of changes in climate is taken into account, events of this magnitude are actually not that unusual. [...] [...] However, the big change in the UAH this month was in the southern hemisphere, continuing to decline to -0.21C from 0.02C the previous month. Update: RSS reports a global increase of +0.06C and southern hemisphere change of -0.12C. It will be interesting to see what happens to global temperatures in March 2008. In past years, downswings in temperatures have rapidly rebounded to higher levels. There is some evidence that this downswing corresponds with a discrete change in ocean circulation, in which case we may not see a rebound this time. Here are the links to the data sets. OrganizationNameURL Remote Sensing SystemsRSSftp://ftp.ssmi.com/msu/monthly_time_series/rss_monthly_msu_amsu_channel_tlt_anomalies_land_and_ocean_v03_1.txt Uni. Alabama HuntsvilleUAHhttp://vortex.nsstc.uah.edu/public/msu/t2lt/tltglhmam_5.2 NASAGISShttp://data.giss.nasa.gov/gistemp/tabledata/GLB.Ts+dSST.txt Hadley CenterCRUhttp://hadobs.metoffice.com/hadcrut3/diagnostics/global/nh+sh/monthly Predictably, there has also been much side-talk on the blogs about ‘a single year does not a trend make’. For the record, I did an analysis here which showed that when the non-normality of changes in climate is taken into account, events of this magnitude are actually not that unusual. [...]

]]> By: admin http://landshape.org/enm/surface-temperatures/#comment-5978 admin Thu, 28 Feb 2008 10:50:49 +0000 http://landshape.org/enm/surface-temperatures/#comment-5978 John, You are right, the estimate is less accurate because it is only a sample. To me, the distribution looks Leptokurtic, the probability distribution is simultaneously “peaked” and has “fat tails.” So you would have to test for these and fit an appropriate distribution. Actually it looks too frequent to me too. I think that the runs are longer in the earlier portion of the temperature record, probably because there were fewer sites then, so the variance is higher. It would be worth trying to estimate the actual variance for the recent period of data collection. Because the present day data has lower variance and greater reliability, then runs may be less common. Just a guess at this stage. John, You are right, the estimate is less accurate because it is only a sample. To me, the distribution looks Leptokurtic, the probability distribution is simultaneously “peaked” and has “fat tails.” So you would have to test for these and fit an appropriate distribution.

Actually it looks too frequent to me too. I think that the runs are longer in the earlier portion of the temperature record, probably because there were fewer sites then, so the variance is higher. It would be worth trying to estimate the actual variance for the recent period of data collection. Because the present day data has lower variance and greater reliability, then runs may be less common. Just a guess at this stage.

]]> By: admin http://landshape.org/enm/surface-temperatures/#comment-6262 admin Thu, 28 Feb 2008 10:50:00 +0000 http://landshape.org/enm/surface-temperatures/#comment-6262 John, You are right, the estimate is less accurate because it is only a sample. To me, the distribution looks Leptokurtic, the probability distribution is simultaneously “peaked” and has “fat tails.” So you would have to test for these and fit an appropriate distribution. Actually it looks too frequent to me too. I think that the runs are longer in the earlier portion of the temperature record, probably because there were fewer sites then, so the variance is higher. It would be worth trying to estimate the actual variance for the recent period of data collection. Because the present day data has lower variance and greater reliability, then runs may be less common. Just a guess at this stage. John, You are right, the estimate is less accurate because it is only a sample. To me, the distribution looks Leptokurtic, the probability distribution is simultaneously “peaked” and has “fat tails.” So you would have to test for these and fit an appropriate distribution.

Actually it looks too frequent to me too. I think that the runs are longer in the earlier portion of the temperature record, probably because there were fewer sites then, so the variance is higher. It would be worth trying to estimate the actual variance for the recent period of data collection. Because the present day data has lower variance and greater reliability, then runs may be less common. Just a guess at this stage.

]]> By: John G. Bell http://landshape.org/enm/surface-temperatures/#comment-5977 John G. Bell Wed, 27 Feb 2008 22:47:10 +0000 http://landshape.org/enm/surface-temperatures/#comment-5977 Thanks for the reply. I was looking at the wrong tail. So if the drop had been 0.01 more we'd be summing the tail of the -0.7 class. 0+0+2+2+4=8 8/1885=0.00424 or once every 19.6 years and if the drop was up to 0.09 less it would still be a one in 6 year event. Somehow that doesn't seem right even if we pretend HadCRU month data is accurate to 0.01 degree C. If we fitted a curve to the data and solved for the area of the tail to the left of -0.5906 would it still be a one in 6 year event? It has been 35 years since I've done these sort of things ... About the number of years since the US has had so much snow cover :). Sorry if the answer is obvious. Thanks for the reply. I was looking at the wrong tail. So if the drop had been 0.01 more we’d be summing the tail of the -0.7 class. 0+0+2+2+4=8 8/1885=0.00424 or once every 19.6 years and if the drop was up to 0.09 less it would still be a one in 6 year event.

Somehow that doesn’t seem right even if we pretend HadCRU month data is accurate to 0.01 degree C.
If we fitted a curve to the data and solved for the area of the tail to the left of -0.5906 would it still be a one in 6 year event? It has been 35 years since I’ve done these sort of things … About the number of years since the US has had so much snow cover :) . Sorry if the answer is obvious.

]]> By: John G. Bell http://landshape.org/enm/surface-temperatures/#comment-6261 John G. Bell Wed, 27 Feb 2008 22:47:00 +0000 http://landshape.org/enm/surface-temperatures/#comment-6261 Thanks for the reply. I was looking at the wrong tail. So if the drop had been 0.01 more we'd be summing the tail of the -0.7 class. 0+0+2+2+4=8 8/1885=0.00424 or once every 19.6 years and if the drop was up to 0.09 less it would still be a one in 6 year event. Somehow that doesn't seem right even if we pretend HadCRU month data is accurate to 0.01 degree C. If we fitted a curve to the data and solved for the area of the tail to the left of -0.5906 would it still be a one in 6 year event? It has been 35 years since I've done these sort of things ... About the number of years since the US has had so much snow cover :). Sorry if the answer is obvious. Thanks for the reply. I was looking at the wrong tail. So if the drop had been 0.01 more we’d be summing the tail of the -0.7 class. 0+0+2+2+4=8 8/1885=0.00424 or once every 19.6 years and if the drop was up to 0.09 less it would still be a one in 6 year event.

Somehow that doesn’t seem right even if we pretend HadCRU month data is accurate to 0.01 degree C.
If we fitted a curve to the data and solved for the area of the tail to the left of -0.5906 would it still be a one in 6 year event? It has been 35 years since I’ve done these sort of things … About the number of years since the US has had so much snow cover :) . Sorry if the answer is obvious.

]]> By: admin http://landshape.org/enm/surface-temperatures/#comment-5976 admin Wed, 27 Feb 2008 20:15:46 +0000 http://landshape.org/enm/surface-temperatures/#comment-5976 John, summing the tail of the distribution to the -0.6 class gives 0+0+2+2+4+18=26 counts. This gives a monthly probability of 26/1885=0.0138, a probability of it occurring in a year of 12*0.0138=0.166 and an expected recurrence of 1/0.166=6 years. I have corrected the post. This should be about right for estimating the probabilities given on explanation like volcanic eruptions. The probability should be higher (less unusual) if there are eruptions as the cooling would be explained. These temperatures are 12 months apart, (or 364 days). I might look at the 13month statistics when they come out. If you are looking for a one in one hundred year event (0.01) my guess is that it would take another year of falling temperatures to get there. Sorry about the delay, but I am getting so much spam now I have to moderate. John, summing the tail of the distribution to the -0.6 class gives 0+0+2+2+4+18=26 counts. This gives a monthly probability of 26/1885=0.0138, a probability of it occurring in a year of 12*0.0138=0.166 and an expected recurrence of 1/0.166=6 years. I have corrected the post.

This should be about right for estimating the probabilities given on explanation like volcanic eruptions. The probability should be higher (less unusual) if there are eruptions as the cooling would be explained.

These temperatures are 12 months apart, (or 364 days). I might look at the 13month statistics when they come out. If you are looking for a one in one hundred year event (0.01) my guess is that it would take another year of falling temperatures to get there.

Sorry about the delay, but I am getting so much spam now I have to moderate.

]]> By: admin http://landshape.org/enm/surface-temperatures/#comment-6260 admin Wed, 27 Feb 2008 20:15:00 +0000 http://landshape.org/enm/surface-temperatures/#comment-6260 John, summing the tail of the distribution to the -0.6 class gives 0+0+2+2+4+18=26 counts. This gives a monthly probability of 26/1885=0.0138, a probability of it occurring in a year of 12*0.0138=0.166 and an expected recurrence of 1/0.166=6 years. I have corrected the post. This should be about right for estimating the probabilities given on explanation like volcanic eruptions. The probability should be higher (less unusual) if there are eruptions as the cooling would be explained. These temperatures are 12 months apart, (or 364 days). I might look at the 13month statistics when they come out. If you are looking for a one in one hundred year event (0.01) my guess is that it would take another year of falling temperatures to get there. Sorry about the delay, but I am getting so much spam now I have to moderate. John, summing the tail of the distribution to the -0.6 class gives 0+0+2+2+4+18=26 counts. This gives a monthly probability of 26/1885=0.0138, a probability of it occurring in a year of 12*0.0138=0.166 and an expected recurrence of 1/0.166=6 years. I have corrected the post.

This should be about right for estimating the probabilities given on explanation like volcanic eruptions. The probability should be higher (less unusual) if there are eruptions as the cooling would be explained.

These temperatures are 12 months apart, (or 364 days). I might look at the 13month statistics when they come out. If you are looking for a one in one hundred year event (0.01) my guess is that it would take another year of falling temperatures to get there.

Sorry about the delay, but I am getting so much spam now I have to moderate.

]]> By: John G. Bell http://landshape.org/enm/surface-temperatures/#comment-5975 John G. Bell Wed, 27 Feb 2008 00:08:19 +0000 http://landshape.org/enm/surface-temperatures/#comment-5975 Isn't that 6/1885 or 0.00318? That would be once every 26.2 years. How many of these months back to back would be unusual? Remember we have no volcanic eruption to blame this cooling on. As we are into small numbers, would it be better to look at temps 364 days apart? Thanks Isn’t that 6/1885 or 0.00318? That would be once every 26.2 years. How many of these months back to back would be unusual? Remember we have no volcanic eruption to blame this cooling on. As we are into small numbers, would it be better to look at temps 364 days apart?
Thanks

]]> By: John G. Bell http://landshape.org/enm/surface-temperatures/#comment-6259 John G. Bell Wed, 27 Feb 2008 00:08:00 +0000 http://landshape.org/enm/surface-temperatures/#comment-6259 Isn't that 6/1885 or 0.00318? That would be once every 26.2 years. How many of these months back to back would be unusual? Remember we have no volcanic eruption to blame this cooling on. As we are into small numbers, would it be better to look at temps 364 days apart? Thanks Isn’t that 6/1885 or 0.00318? That would be once every 26.2 years. How many of these months back to back would be unusual? Remember we have no volcanic eruption to blame this cooling on. As we are into small numbers, would it be better to look at temps 364 days apart?
Thanks

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