If Mann's data or methodology was flawed, his charts error bands or confidence intervals or whatever term you want, would be flawed too.
But you mentioning the chart made me decide to take a look at the original Mann chart. I believe it is the first one at this site - figure 1:
worldclimatereport.com
You expressed an interest in some other charts of the period Mann charted. The site has a couple of them. Check out figures 2, 3, and 4. Hope you find them informational.
.............
The third dissenting voice was that of Jan Esper and colleagues in 2004. Esper is an expert in climate reconstructions based upon tree-ring records (the primary type of proxy data relied upon by Mann et al. in creating the “hockey stick”). It turns out that one must be careful when using tree rings to reconstruct long-term climate variability because as the tree itself ages, the widths of the annual rings that it produces changes—even absent any climatic variations. This growth trend needs to be taken into account when trying to interpret any climate data contained in the tree-ring records. In most cases, the tree-ring records are first detrended to remove this growth trend, and then the remaining variation in the rings is used to derive a climate signal. The problem with this technique is that by detrending the tree-ring record, long-term climate trends are lost as well. Esper et al. point out that this could be one likely reason why the handle of the “hockey stick” is so flat—it lacks the centennial-scale variations that were lost in the standardization of its primary data source. Using an alternative technique that attempted to preserve as much of the information about long-term climate variations as possible from historical tree-ring records, Esper and colleagues derived their own annual Northern Hemisphere temperature reconstruction. The result (Figure 2) is a 1,000-yr temperature history in which the LIA and the MWP are much more pronounced than the “hockey stick” reconstruction—more evidence that the “hockey stick” underestimates the true level of natural climate variation.
Figure 2. A comparison of 1,000-year temperature reconstructions. The red line is the temperature history of the Northern Hemisphere as developed by Mann and colleagues, a.k.a. “the Hockey Stick.” The blue line represents the Northern Hemispheric temperature history as constructed by Esper’s research team (source: Esper et al., 2002).
The chorus of dissent grew louder with the publication of a paper by Hans von Storch and colleagues in Science in late-2004. Von Storch was interested in how well the temperature reconstruction methodology used in producing the “hockey stick” actually worked. In order to investigate this, he used a climate model, run with historic changes in solar output and volcanic eruptions to produce a temperature record for the past 1,000 years. For von Storch’s purposes, it was not necessary to produce an accurate temperature record, just one that was reasonably representative of what may have happened. Next, he employed a methodology similar to Mann et al.’s, using “proxy” data derived from the climate model temperature record to see how well the Mann et al. methodology could reconstruct the actual data from which it was drawn. What von Storch’s research team found was that the techniques used to construct the “hockey stick” vastly underestimated the true level of variability in the known (modeled) temperature record (Figure 3). It is thus reasonable to conclude that the same techniques, when applied in the real world, would similarly underestimate the true level of natural variability and thus underplay the importance of the LIA and MWP. Again, the von Storch finding adds further evidence that the handle of the “hockey stick” is too flat.
Figure 3. Modeled temperature history for the past 1,000 years (black line) and attempts to reconstruct that history using a Mann-like multi-proxy technique when different amounts of noise are included (colored lines). The more noise, the lower the variance. (Source: von Storch et al., 2004).
And now, with the publication of a paper in Nature magazine in early 2005 by Anders Moberg and colleagues, it’s all over for the hockey stick. Recognizing that different kinds of proxy temperature records may be more appropriately related to climatic variations at different time scales, Moberg applied a statistical technique called ‘wavelet analysis’ that allows each proxy to explain temperature variations on a timescale that it was most sensitive to. For example, as discussed above, tree-rings have difficulty in capturing long-term variations but are quite useful for investigating annual-to-decadal scale variability. Other proxies, such as lake and ocean sediments, contain climate information, but are harder to date precisely on annual or even decadal time scales. These low temporal resolution proxies are nonetheless useful for capturing long-term, multi-century climate variations. By combining high-resolution with low-resolution proxy information, Moberg et al. produced a 1,000-yr (actually a 2,000-yr) long temperature reconstruction for the Northern Hemisphere. Moberg’s reconstruction (Figure 4) contains strong MWP and LIA signals. The natural variation of temperatures in the Moberg reconstruction is two to three times that of the Mann et al. “hockey stick.” Again, the handle of the “hockey stick” was found to be too flat.
Figure 4. The low-frequency component of climate as determined by Moberg et al. (blue curve with shaded uncertainty bands) compared with the Mann et al. record (orange curve and shaded uncertainty band). (Source: Moberg et al., 2005).
Had the original reconstruction by Mann and colleagues looked like the latest reconstruction by Moberg et al., no one would have paid it much attention, because it would have fit nicely with the expectations given all of the prior research on the climate history of the past millennium. It would have been nothing remarkable.
But, the “hockey stick” was remarkable. And as such, it will be remembered as a remarkable lesson in how fanaticism can temporarily blind a large part of the scientific community and allow unproven results to become mainstream thought overnight. The embarrassment that it caused to many scientists working in the field of climatology will not be soon forgotten. Hopefully, new findings to come, as remarkable and enticing as they may first appear, will be greeted with a bit more caution and thorough investigation before they are widely accepted as representing the scientific consensus.
In this way, the lead graphic in the upcoming IPCC’s Fourth Assessment Report, due out in late 2007, may even survive to be included somewhere in the Fifth Assessment Report which will no doubt follow five or so years hence. The “hockey stick” won’t be so lucky.
References:
Esper J., D.C. Frank, and J.S. Wilson, 2004. Climate reconstructions: Low-frequency ambition and high-frequency ratification. Eos, 85, 133,120.
Esper, J., E.R. Cook, and F.H. Schweingruber, 2002. Low frequency signals in long tree-ring chronologies for reconstructing past temperature variability, Science, 295, 2250-2253.
Intergovernmental Panel on Climate Change, 2001. Climate Change 2001: The Scientific Basis. Houghton, J.T., et al., (eds.), Cambridge University Press, Cambridge, U.K, pp 881, grida.no.
Mann, M.E. R.S. Bradley, and M.K. Hughes, 1998. Global-scale temperature patterns and climate forcing over the past six centuries. Nature, 392, 779-787.
Mann, M.E., R.S. Bradley, and M.K. Hughes, 1999. Northern Hemisphere temperatures during the past millennium: inferences, uncertainties, and limitations. Geophysical Research Letters, 26, 759–762.
McIntyre, S., and R. McKitrick, 2003. Corrections to the Mann et. al. (1998) Proxy database and Northern Hemispheric average temperature series. Energy & Environment,14, 751-771.
McIntyre, S., and R. McKitrick, 2005. Hockey sticks, principal components, and spurious significance. Geophysical Research Letters, 32, doi:10.1029/2004GL021750.
Moberg, A., et al., 2005. Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data. Nature, 433, 613-617.
Soon, W., and S. Baliunas, 2003. Proxy climatic and environmental changes of the past 1,000 years. Climate Research, 23, 89–110.
Von Storch, H., et al., 2004. Reconstructing past climate from noisy data. Science, 306, 679-682.
worldclimatereport.com
Its ridiculous for the GW guys to keep defending the Mann hockey stick chart - its been pretty thoroughly debunked multiple times now. |
