Al Gore's hockey stick version (page 65 of the book "An Inconvenient Truth") is taken from one of the many conflicting versions of Lonnie Thompson's ice core data. Now there is an ongoing controversy about whether Thompson's data is a temperature or precipitation proxy, with pretty much every other scientist except Thompson now viewing the data as more of a precipitation proxy.
There's an interesting and symptomatic change in IPCC wording between the Second Draft and the Final Report, which has the effect of bringing the language more in line with Al Gore.
Here's what Al Gore said:
Nevertheless the so-called global-warming skeptics often say that global warming is really an illusion reflecting nature's cyclical fluctuations. To support this view they frequently refer to the Medieval Warm Period. But as Dr Thompson's thermometer shows, the vaunted Medieval Warm Period (the third little blip from the left below) was tiny compared with the enormous increases in temperature of the last half-century (the red peaks at the far right of the chart).
Those global warming skeptics - a group diminishing almost as rapidly as the mountain glaciers - launched a fierce attack against another measurement of the 1000 year correlation between CO2 and temperature known as the "hockey stick", a grpahic image representing the research of climate scientist Michael Mann and his collegatues. But in fact scientists have confirmed the same basic conclusions in multiple ways - with Thompson's ice core record as one of the most definitive.
Here's an attempt at replicating the graphic in Inconvenient Truth (using the decadal version from Thompson's Climatic Change 2003 article, but as discussed elsewhere, there are many versions of Thompson's data floating around and Thompson has refused to provide sample data to disentangle the mess).
IPCC on Tropical Glaciers
The IPCC has come down on the side that Thompson's ice core data is a precipitation proxy as follows:
Stable isotope data from high-elevation ice cores provide long records and have been interpreted in terms of past temperature variability (Thompson, 2000), but recent calibration and modelling studies, in South America and southern Tibet (Hoffmann et al., 2003; Vuille and Werner, 2005; Vuille et al., 2005), indicate a dominant sensitivity to precipitation changes, at least on seasonal to decadal timescales, in these regions.
Where is the Dendro Truth Squad when we need them? Do you think that they can do ice cores as well? Based on the IPCC, Al Gore's Hockey Stick is simply showing that there is increased precipitation in the 20th century in high altitudes. Of course the increased precipitation may be due to increased warming, but this interpretation of the Thompson ice cores tends to undercut the dire warnings of drought that crop up elsewhere. In the Second Draft, the IPCC continued on, observing that "apparently unprecedented" glacier decline was "possibly" associated with enhanced warming at high altitudes and that other factors besides temperature "can strongly influence" tropical glacier retreat.
Very rapid and apparently unprecedented melting of tropical ice caps has been observed in recent decades (Thompson et al., 2000; Thompson, 2001) (see Box 6.3), possibly associated with enhanced warming at high elevations (Gaffen et al., 2000), but other factors besides temperature can strongly influence tropical glacier mass balance (see Chapter 3).
The unqualified use of "unprecedented" - this could almost be an article in Nature - is an annoying habit that makes climate scientists sound like Creationists. Memo to climate scientists: the earth is more than 4200 years old. There is strong evidence that the Quelccaya glacier is less than 4200 years old and, in my opinion, the evidence for the existence of the Kilimanjaro and Mt Kenya glacier in the Holocene Optimum is virtually non-existent.
Comparing this sentence to the final version, we see that "possibly" has been changed to "likely" and the statement that other factors could affect glacier balance has been removed.
Very rapid and apparently unprecedented melting of tropical ice caps has been observed in recent decades (Thompson et al., 2000; Thompson, 2001; see Box 6.3), likely associated with enhanced warming at high elevations (Gaffen et al., 2000; see Chapter 4).
I haven't seen the version of AR4 that was used in the SPM, so I don't know whether these changes were made before the SPM or after the SPM. It would be nice to know if this particular change was made so that the Report conformed to the SPM or not.
Stable isotope data from high-elevation ice cores provide long records and have been interpreted in terms of past temperature variability (Thompson, 2000), but recent calibration and modelling studies, in South America and southern Tibet (Hoffmann et al., 2003; Vuille and Werner, 2005; Vuille et al., 2005), indicate a dominant sensitivity to precipitation changes, at least on seasonal to decadal timescales, in these regions. Very rapid and apparently unprecedented melting of tropical ice caps has been observed in recent decades (Thompson et al., 2000; Thompson, 2001) (see Box 6.3), possibly associated with enhanced warming at high elevations (Gaffen et al., 2000), but other factors besides temperature can strongly influence tropical glacier mass balance (see Chapter 3).
December 1986 - Irony:
Erice Seminar:
Koutsoyiannis et al 2008: On the credibility of climate predictions:
Caspar Ammann, Texas Sharpshooter:
Sea Ice Stretch Run #2:
McKitrick: What the Hockey Stick Debate is About?:
Chucky and the U.S. CCSP:
Svalgaard #8:
Bishop Hill: Caspar and the Jesus Paper:
Well, well. Look what the cat dragged in.:
Stockwell on CSIRO Drought Report :