Here’s an example of how one can wander off curious little by-ways in trying to replicate Hockey Team materials. I’m working on the seemingly simple task of testing the correlations to gridcell temperature in Osborn and Briffa 2006. One of the series – a "quiet" series – is Fisher’s "West Greenland dO18 Stack". Also with Svalbard in the news so to speak, and Jean S posting up about Norwegian temperatures, I thought it would be interesting to look at some Greenland temperatures as well.
The sites used by Fisher are all about 71N, between 35 and 40W (one at 45W). But one you go to check the HadCRU gridcell, it doesn’t have any values. Nor do the cells to the left or right. The closest gridcell with values was 67N, 37W, one gridcell to the south. You’d think that this might have been what they used, especially since the sites are just a titch north of the gridcell border. But I had some other Hockey Team information to reconcile. Some time ago, I got information from Phil Jones on gridcell blocks used in Jones and Mann 2004 for correlation – here they based the comparison on some kind of average from all gridcells in the blocks 62.5-72.5N; 57.5W-42.5W, i.e. they did not use the closest block. It seemed odd, but, hey, it’s the Hockey Team.
When you look at a map of Greenland, the gridcells used in the Jones and Mann comparison are all on the west coast of Greenland, while there was another set of values for gridcells along the east coast of Greenland, with the center, where the ice cores are, lacking any values. In passing, the ice cores are all drilled from sites that are very high – about 3100 m.
So was there any difference in the temperature histories on the two sides of the island. Here I’ve plotted up the three gridcells with the most values on each side of the island, showing here the plot of monthly values, which contains some texture lost in the annual data. Take a look at the west coast sites in Figure 1 and the east coast sites in Figure 2. I’ve shown "trend" lines in each case. The data goes up to the end of 2004.
Figure 1. HadCRU2 temperature anomalies for three west coast Greenland gridcells.
Figure 2. HadCRU2 temperature anomalies for three east coast Greenland gridcells
A couple of features catch my eye. First, there isn’t a big trend on either coast. Second, the 1930s were warmer than the present, a point we’ve heard on many occasions. Third, the amplitudes of the east coast gridcells is lesas than the west coast gridcells. Fourth, there is little change in upspikes; in "warm" periods, what you see is more an absence of downspikes, which characterize the late 19th century. Any slight trend in a couple of gridcells is dependent on these 19th century downspikes. I’m not drawing any conclusions from it, but there is no obvious "Arctic amplification" here; in fact, there is none. So if one of the fingerprints is Arctic amplification, CSI could find no fingerprints at this crime scene. The Hockey Team must have wiped off the prints and "moved on".
I made annual averages of the west coast and east coast gridcells and these ended up being pretty similar and look more or less like the individual gridcells.
Next, I compared Fisher’s dO18 stack to the west coast gridcell average (using the presumed Jones and Mann comparand.) The top panel below shows the dO18 series from 8000 to the present and the bottom panel compares the dO18 re-scaled to have the same scale as the instrumental record in the 1800-2000 period.
Figure 3. Top – Fisher dO18 stack; bottom – black -Fisher dO18 stack rescaled; red- west coast Greenland gridcell average.
Again, there are lots of interesting features to this plot. The dO18 series has remarkably little centennial variation. It has no Little Ice Age or MWP. (It was incorporated as a canonical Hockey Team series by Bradley and Jones 1993, arguing against the Little Ice Age, and has been used in virtually every Hockey Team study since then.) No wonder Bradley and Jones like it. The only problem is that it doesn’t have a 20th century pulse either. But if you splice in some short HS-shaped series to force a blade (e.g. Jacoby NH or C England documentary, that type of thing), it’s a great series for making a hockey stick shaft, if htat’s what you want to do.
Fisher 1996 (NATO) noted this lack of centennial texture, but placed in a broader context. He noted that this set of cores (and also GISP2) had very little centennial variability throughout the entire Holocene. In this respect, they were very different from many other cores (e.g. Agassiz, Devon) which had very warm Holocene Optimum – significantly warmer than modern or medieval – and considerable centennial variability. Fisher noted the problem, but had no firm explanation. He posited that the GISP2 and the Fisher stack cores were very high and he speculated that their very coldness and remoteness made them less susceptible to change. As an analogy, think of a LIFO inventory – this is the inventory base that never gets changed. Anyway, Fisher had no explanation -he said, however, that, until you solved the big problem of Holocene lack of variability, it was mere trifling to to worry about centennial variability. Fisher, by the way, did not have a Hockey Team approach to data. I asked him in November 2003 about one of his studies, just after MM03. He inundated me with data; he sent me a diskette with lots of data and copies of numerous interesting papers.
Looking at the proxy and temperature average on a similar scale, one thought does occur to me. In the warm 1930s, the dO18 record continues to have major downspikes that are not present in the temperature record. Now in the monthly temperature histories, there were more 19th century downspikes than 20th century downspikes. The gridcell histories are based on more moderate coastal records, maybe the cold period downspikes continue to be prevalent at altitude. Just musing.
There are other factors in accumulation of annual dO18 records. There is far more variation within a single year in dO!8 levels from summer to winter than there is interannually. The majority of accumulation is in the summer. Fisher notes that individual stormy years (1916) show up in the record. To the extent that the dO18 is a temperature record of this high-altitude location, there is even less evidence of 20th century uniqueness in this record than in the coastal gridcells.
It has decent correlation to the gridcell average (.5), but would serve as a classic example of a proxy where most of the correlation comes from high-frequency scales, since it has negligible centennial variability. Briffa and others validate the use of this proxy because of its correlation (r) to gridcell temperature. Wait a minute, didn’t we just read the Hockey Team en masse saying that the r2 was an invalid statistic? And aren’t they using the correlation r here (and everywhere) to validate proxies? I guess it was the squaring process that made it invalid.
Climate Audit 
13 Comments
What proof is there that dO18 is a proxy for temperature? Isn’t there evidence that the correlation goes one way in the tropics and another in the temperate and Arctic zones? Is this another case, like tree rings, of a multi-variable proxy that is simply assumed to be linear with temperature? Wouldn’t lack of correlation be the simplest explanation for the essentially noise like behavior in the plots?
Would you please leave out the trend lines in your plots? These are non-linear systems and a trend line can make it harder to see the ups and downs. It’s not as bad the the big fat multi-year moving averages that get plotted over so much of the climate data, but it does send a message that may not be in the data. Sorry for ranting about my pet peeve.
1. The correlation is impressive actually (visually). Yes it is based on year to year, but any reason to think that if centenial did occur that it wouldn’t follow it?
2. Numerical expression of the “negligable centenial variation”? (Visually it seems like there is some decent difference 1850-1925 and 1925-2000.)
3. wonder if there is some consistent lag. Doesn’t seem to work. Almost that the d18 both anticipates and lags. Wouldn’t know how it would do that though.
Re #1
What proof is there that dO18 is a proxy for temperature? (It’s usually d18O BTW)
That’s the essential question which has been studied intensely. After all the isotope thermometer only works when it snows. At higher lattitudes, there is a clear distinction between winter and summer d18O in precipitation, around 20 mil at some places, partly because of the temperature at the condensation point, partly because of the Rayleigh effect (raining out of heavy isotopes first) due to the longer distance to the main vapor source in winter (ice cover, open water further away).
This annual variation is clearly visible in high resolution proxies of the top layers of ice cores. However, when the snow layers on the ice sheet compress. the annual layers start mixing and the seasonal differences starts to fade. So when the seasonal extremes approach the average, it is weighted average, or the volume of winter snow times the “cold” isotopes versus the volume of summer snow times “warm” isotopes. So this means that the average isotope value is very sensitive to seasonal variations of precipitation. A dry summer looks actually as a cold year, as there are not enough “warm” isotopes to balance.
Ths way, the isotopes are prone to be misunderstood when large changes in precipitation occur in certain era’s
In the case of Greenland (and the rest of Denmark), there is no need to rely only on HadCRU2. The Danish Mateorological Institute (DMI) has kindly published a lot of their data, see here (especially reports 05-05, 06-08, and 06-10). In general, those interested in arctic climate should check, addition to previously mentioned NordKlim, also NARP Climate Dataset (see also here).
Steve, I think you might me interested in this project; some related publications can be downloaded from here (see especially Isaksson et al (2005)).
#3 Thanks
i.e., drought and cold are indistinguishable.
So we do have a situation like the tree rings, though possibly less complicated. There are multiple factors that contribute to the concentration and unless all of them are known simultaneously d18O is not going to be a good thermometer.
Carl Wunsch has written convincingly about Greenland isotopes. As far as I’m concerned, Wunsch is one of the few scientists in the field whose work you can totally rely on.
Great tip, Steve thanks, although he seems to specialize in oceanography. http://puddle.mit.edu/~cwunsch/
Re #4. Attempts to assess and repair the isotope problems have been done by Jeffrey Severinghaus, Richard Alley, Jean Jouzel, Georg Hoffmann et al (google names) by crosschecking the behavior of several other isotopes 40AR, 15N etc. There are also borehole temperature with Dye-3 clearly showing the Medieval Warm period and the Little ice Age
See:
But many things remain suppositions that could be wrong when other elements are not taken into accoung.
GEOPHYSICAL RESEARCH LETTERS, VOL. 27, NO. 5, PAGES 735-738, MARCH 1, 2000
Andreas Inderm¨uhle, Eric Monnin, Bernhard Stau er, Thomas F. Stocker
I would think that diurnal, day to day and annual temperature variations in the inland areas of Greenland would exceed those along the coasts. Of course the ice mass in the interior would sink heat and somewhat moderate it, but at the end of the day, there is more outbound IR in the inland area. For example, mere innate relative humdity is lower there. That part of the world also gets lots of advection fog and stratus – I’d have to believe the interior to be above it. And then, and then … 😉
Interesting to note the article by Petr Chylek just out in GRL. The abstract reads:
“We provide an analysis of Greenland temperature records to compare the current (1995–2005) warming period with the previous (1920–1930) Greenland warming. We find that the current Greenland warming is not unprecedented in recent Greenland history. Temperature increases in the two warming periods are of a similar magnitude, however, the rate of warming in 1920–1930 was about 50% higher than that in 1995–2005”.
They studied the two periods to see if the warming shown in 1995-2005 was unprecedented, and found there was “no statistically significant difference between the average temperature from the 1905 to 1955 period and 1995 to 2005 period”. Statistics buffs will want to check their z-scores.
In their summation, they state: ” Although there has been a considerable temperature increase during the last decade (1995 to 2005) a similar increase and at a faster rate occurred during the early part of the 20th century (1920 to 1930) when carbon dioxide or other greenhouse gases could not be a cause. The Greenland warming of 1920 to 1930 demonstrates that a high concentration of carbon dioxide and other greenhouse gases is not a necessary condition for period of warming to arise. The observed 1995–2005 temperature increase seems to be within a natural variability of Greenland climate’.
Finally: ” To summarize, we find no direct evidence to support the claims that the Greenland ice sheet is melting due to increased temperature caused by increased atmospheric concentration of carbon dioxide. The rate of warming from 1995 to 2005 was in fact lower than the warming that occurred from 1920 to 1930. The temperature trend during the next ten years may be a decisive factor in a possible detection of an anthropogenic part of climate signal over area of the Greenland ice sheet”.
Reference: Chylek, P., M. K. Dubey, and G. Lesins (2006), Greenland warming of 1920–1930 and 1995–2005, Geophys. Res. Lett., 33, L11707, doi:10.1029/2006GL026510, here
sorry, I’ll try again:
Reference: Chylek, P., M. K. Dubey, and G. Lesins (2006), Greenland warming of 1920–1930 and 1995–2005, Geophys. Res. Lett., 33, L11707, doi:10.1029/2006GL026510 here
re #10: There is another interesting article (with Jones & Briffa as co-authors!):
Vinther, B. M.; Andersen, K. K.; Jones, P. D.; Briffa, K. R.; Cappelen, J.,
Extending Greenland temperature records into the late eighteenth century,
J. Geophys. Res., Vol. 111, No. D11, D11105
doi:10.1029/2005JD006810
Seems to me that if there is something one wants to call “unprecedented in recent Greenland history”
it is the shift of 1920’s and 1930’s. I wonder how polar bears survived that period 😉
PDF and data available here.
Abstract:
where can you find the highs and lows of the temperature in Greenland? (school project)please I need help I am computer intolerant.