Ainda a propósito do “Hockey Stick”

O Blog do World Climate Report dá também uma “tacada mortal” ao sinistro taco de hóquei. Num Post de 2005 intitulado “Hockey Stick, 1998-2005, R.I.P.” são ainda apresentados mais elementos que contradizem a teoria de M. Mann.

Eis um extracto significativo:

The “hockey stick” representation of the temperature behavior of the past 1,000 years is broken, dead. Although already reeling from earlier analyses aimed at its midsection, the knockout punch was just delivered by Nature magazine. Thus the end of this palooka: that the climate of the past millennium was marked by about 900 years of nothing and then 100 years of dramatic temperature rise caused by people. The saga of the “hockey stick” 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 “Hockey Stick” is dead. This once-feared icon of global warming purported to show annual average temperature of the Northern Hemisphere for the past 1,000 years. It was derived from the climatic information that is stored in a variety of climate-sensitive or climate “proxy” data records—things such as tree rings, coral banding records, and sediment cores. It’s called the “hockey stick” because its long handle corresponds to 900 years (from 1000 to 1900) of little temperature variation, and its blade represents 100 years (1900 to 1999) of rapid temperature rise (Figure 1). The “hockey stick” made its debut in the journal Geophysical Research Letters in 1999 in a paper by Michael Mann, Raymond Bradley, and Malcolm Hughes that built upon a 1998 paper by the same authors in the journal Nature which detailed the methodology for creating a proxy temperature reconstruction.

Este post dedicada muito espaço ao conceituado H.von Storch e a um artigo publicado em 2004 na Science. (H. von Storch et al., 2004). Mais uma vez é realçado o facto de que o Taco de Hóquei é muito plano nos séculos anteriores, dando a ideia errada sobre a amplitude do período quente medieval e da pequena idade do gêlo.

rip3.gif

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).

O que a equipa de H. von Storch descobriu, e que a figura em cima mostra bem foi que:

” […] 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.”

Moberg et al. (2005), utilizando a “wavelet analysis” chegam a conclusões próximas de H.von Storch e diferentes de M. Mann. O gráfico em baixo mostra as diferenças entre os resultados de M.Mann e Moberg.

rip4.gif

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).

Referências:

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.

Moberg, A., et al., 2005. Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data. Nature, 433, 613-617.

von Storch et al. (2004) – Reconstructing Past Climate from noisy data. Science, 306, pp. 679-682.

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