2 ms·

What's your critique of the hockey stick graph? In what sense was it an error, let alone a "monumental" one?

by scarmig 14y ago

run4yourlives 14y ago
The main issue with any "Hockey Stick" as presented is the length of the shaft. The stick all but vanishes when you look at a long term climate projection, rather than the last 500 years or so.
- moultano 14y ago
  [citation needed]
  - run4yourlives 14y ago
    http://www.intellicast.com/Community/Content.aspx?a=194 http://www.intellicast.com/Community/Content.aspx?a=194
gd1 14y ago
The flaws are numerous, but the easiest to explain is that they employ a post-hoc screening bias. Imagine that you gather a few dozen time-series together. They go back two thousand years. Then you regress them against the (very short) instrumental temperature record in the period where they overlap. You keep the ones that pass and throw the rest away. You form some sort of linear weighted average of the selected proxies (i.e. PCA for example). The thing about this process is, if you feed in completely random red-noise time series you will get a hockey stick. The reason is simple, the selection period will mirror the instrumental temperature (mental check: it has to, after all we only selected the proxies that matched the instrumental temperature). You have your blade. But none of those red noise proxies actually reflect past temperature do they? They just happened to be selected by random chance. So in the time before the selection period, the noise cancels out and you have a flat line. There is your stick. This is the core of how these "proxy reconstructions" work, and it is nonsense. Outside of that, it gets even better. The stories are comical and numerous. Mann famously fed a contaminated Finnish lake sediment series into his algo, which happily regressed it against temperature and found that it passed significance if it was used upside down (in the opposite orientation to that suggested by the author in the original source paper). So in it went. GIGO. Or how about the question of which temperature series to regress against? You'd think you'd regress against local temperature right? Or maybe at least the same continent? Oh ye optimistic fool, go and google "teleconnection" and "non-local statistical relationship". This is what passes as "climate science".
- scarmig 14y ago
  If I provided multiple independent reconstructions of historical temperatures, would you change your position and accept the scientific consensus?
  - gd1 14y ago
    Does it sound by my post that I am ignorant of these "multiple" reconstructions? They all use the same proxies and similar techniques, Esper, Briffa, bristle cones, etc. I have read a good number of them. They are all awful. Paleoclimatology isn't any worse than some other soft sciences I guess - the difference is that there isn't so much riding on them being right.
    - scarmig 14y ago
      For the interested, check out Wahl and Ammann 2007 that addresses the simplistic criticism that gd1 offers.
      - eqreqeq 14y ago
        Thanks. It would definitely have been better for those listening to this discussion to hear your counterpoints rather than me having to go look it up in a sea of words. Especially since I'm not really interested in the field. Also, you called his criticism simplistic without explaining why. Not very good manners.
      - kevinskii 14y ago
        Wahl and Ammann 2007 does not appear to adequately address gd1's points. It just applies a slightly different statistical approach using the same flawed premise. There are countless arguments and rebuttals to be found on both sides of the debate, but I've found the ones below to be particularly helpful: Pro Hockey Stick: [1] Original MBH98 paper (PDF): http://stephenschneider.stanford.edu/Publications/PDF_Papers/MannBradleyHughes1998.pdf http://stephenschneider.stanford.edu/Publications/PDF_Papers... [2] Wahl and Ammann 2007 (PDF): http://www.cgd.ucar.edu/ccr/ammann/millennium/refs/Wahl_ClimChange2007.pdf http://www.cgd.ucar.edu/ccr/ammann/millennium/refs/Wahl_Clim... [3] Wikipedia article: http://en.wikipedia.org/wiki/Hockey_stick_controversy http://en.wikipedia.org/wiki/Hockey_stick_controversy [4] Real Climate Hockey Stick "Dummies Guide" (PDF): http://www.realclimate.org/dummies.pdf http://www.realclimate.org/dummies.pdf Skeptical of Hockey Stick: [5] Skeptic blog post "Casper and the Jesus Paper": http://bishophill.squarespace.com/blog/2008/8/11/caspar-and-the-jesus-paper.html http://bishophill.squarespace.com/blog/2008/8/11/caspar-and-... [6] "The Hockey Stick Illusions" book (same skeptic author): http://www.amazon.com/The-Hockey-Stick-Illusion-Climategate/dp/1906768358/ref=cm_cr_pr_product_top http://www.amazon.com/The-Hockey-Stick-Illusion-Climategate/... [7] McIntyre & McKitrick 2003 (PDF): http://climateaudit.files.wordpress.com/2005/09/mcintyre.mckitrick.2003.pdf http://climateaudit.files.wordpress.com/2005/09/mcintyre.mck...

What's your critique of the hockey stick graph? In what sense was it an error, let alone a "monumental" one?

by scarmig 14y ago

What's your critique of the hockey stick graph? In what sense was it an error, let alone a "monumental" one?

The main issue with any "Hockey Stick" as presented is the length of the shaft. The stick all but vanishes when you look at a long term climate projection, rather than the last 500 years or so.

moultano 14y ago
[citation needed]
- run4yourlives 14y ago
  http://www.intellicast.com/Community/Content.aspx?a=194 http://www.intellicast.com/Community/Content.aspx?a=194

gd1 14y ago

The flaws are numerous, but the easiest to explain is that they employ a post-hoc screening bias. Imagine that you gather a few dozen time-series together. They go back two thousand years. Then you regress them against the (very short) instrumental temperature record in the period where they overlap. You keep the ones that pass and throw the rest away. You form some sort of linear weighted average of the selected proxies (i.e. PCA for example). The thing about this process is, if you feed in completely random red-noise time series you will get a hockey stick. The reason is simple, the selection period will mirror the instrumental temperature (mental check: it has to, after all we only selected the proxies that matched the instrumental temperature). You have your blade. But none of those red noise proxies actually reflect past temperature do they? They just happened to be selected by random chance. So in the time before the selection period, the noise cancels out and you have a flat line. There is your stick. This is the core of how these "proxy reconstructions" work, and it is nonsense. Outside of that, it gets even better. The stories are comical and numerous. Mann famously fed a contaminated Finnish lake sediment series into his algo, which happily regressed it against temperature and found that it passed significance if it was used upside down (in the opposite orientation to that suggested by the author in the original source paper). So in it went. GIGO. Or how about the question of which temperature series to regress against? You'd think you'd regress against local temperature right? Or maybe at least the same continent? Oh ye optimistic fool, go and google "teleconnection" and "non-local statistical relationship". This is what passes as "climate science".

scarmig 14y ago
If I provided multiple independent reconstructions of historical temperatures, would you change your position and accept the scientific consensus?
- gd1 14y ago
  Does it sound by my post that I am ignorant of these "multiple" reconstructions? They all use the same proxies and similar techniques, Esper, Briffa, bristle cones, etc. I have read a good number of them. They are all awful. Paleoclimatology isn't any worse than some other soft sciences I guess - the difference is that there isn't so much riding on them being right.
  - scarmig 14y ago
    For the interested, check out Wahl and Ammann 2007 that addresses the simplistic criticism that gd1 offers.
    - eqreqeq 14y ago
      Thanks. It would definitely have been better for those listening to this discussion to hear your counterpoints rather than me having to go look it up in a sea of words. Especially since I'm not really interested in the field. Also, you called his criticism simplistic without explaining why. Not very good manners.
    - kevinskii 14y ago
      Wahl and Ammann 2007 does not appear to adequately address gd1's points. It just applies a slightly different statistical approach using the same flawed premise. There are countless arguments and rebuttals to be found on both sides of the debate, but I've found the ones below to be particularly helpful: Pro Hockey Stick: [1] Original MBH98 paper (PDF): http://stephenschneider.stanford.edu/Publications/PDF_Papers/MannBradleyHughes1998.pdf http://stephenschneider.stanford.edu/Publications/PDF_Papers... [2] Wahl and Ammann 2007 (PDF): http://www.cgd.ucar.edu/ccr/ammann/millennium/refs/Wahl_ClimChange2007.pdf http://www.cgd.ucar.edu/ccr/ammann/millennium/refs/Wahl_Clim... [3] Wikipedia article: http://en.wikipedia.org/wiki/Hockey_stick_controversy http://en.wikipedia.org/wiki/Hockey_stick_controversy [4] Real Climate Hockey Stick "Dummies Guide" (PDF): http://www.realclimate.org/dummies.pdf http://www.realclimate.org/dummies.pdf Skeptical of Hockey Stick: [5] Skeptic blog post "Casper and the Jesus Paper": http://bishophill.squarespace.com/blog/2008/8/11/caspar-and-the-jesus-paper.html http://bishophill.squarespace.com/blog/2008/8/11/caspar-and-... [6] "The Hockey Stick Illusions" book (same skeptic author): http://www.amazon.com/The-Hockey-Stick-Illusion-Climategate/dp/1906768358/ref=cm_cr_pr_product_top http://www.amazon.com/The-Hockey-Stick-Illusion-Climategate/... [7] McIntyre & McKitrick 2003 (PDF): http://climateaudit.files.wordpress.com/2005/09/mcintyre.mckitrick.2003.pdf http://climateaudit.files.wordpress.com/2005/09/mcintyre.mck...