World Climate Report: Mann et al.’s "Hockey Stick", 1998-2005, R.I.P.
Filed under: Climate History, Paleo/Proxy, Temperature History —
"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” theory is now discredited: How it quickly became the poster child for anthropogenic global warming.
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.
]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).
Figure 1. Mann et al.’s “hockey stick”—the multi-proxy temperature reconstruction of the Northern Hemisphere for the past 1,000 years (blue line with gray shading depicting confidence bands). The red line is the temperature data from actual observations. (Source: Intergovernmental Panel on Climate Change 2001).
However, the shape of the “hockey stick” looked strangely out of place against the existing knowledge of the climate of the past millennium. Where was the Little Ice Age (LIA)—a well-documented cold period lasting from about the 16th to the 19th century? And where was the Medieval Warm Period (MWP)—a relatively warmer period extending from about 11th to the 13th century? By containing little indication that these climate episodes existed, the “hockey stick” presents a completely new picture of the climate of the past 1,000 years
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).
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.
Please also see: http://www.john-daly.com/hockey/hockey.htm