Yesterday, I posted up about “Dr Thompson’s Thermometer” and, thanks to CA readers, some interesting results emerged. A special thanks to Tim Lambert for spotting the provenance of Dr Thompson’s thermometer. The post today will repeat some of yesterday’s material, but will recast it, since we now understand the puzzle much better. In Inconvenient Truth, after a segment discussing glaciers, Gore stands in front of a Hockey Stick graph for the last 1000 years and tells his audience that “Dr Thompson’s thermometer” had shown the inconsequentiality of the Medieval Warm Period and, [in the book Nov 13], that “Thompson’s ice core record [was] one of the most definitive” confirmations of Mann’s Hockey Stick. [The text in the book says:]
Lonnie and his team of experts then examine the tiny bubbles of air trapped in the snow in the year that it fell. They can measure how much CO2 was in the Earth’s atmosphere in the past year by year. They can also measure the exact temperature of the atmosphere each year by calculating the ratio of different isotopes of oxygen which provides an ingenious and highly accurate thermometer. The team can count backward in time year by year – the same way an experienced forester can read tree rings – by simply observing the clear line od demarcation that separates each year from the one preceding it as seen in this unique frozen record. The thermometer to the right measures temperature in the Northern Hemisphere over the past 1000 years. The blue is cold and the red is hot. The bottom of the graph marks 1000 years ago and the current era is at the top.
The correlation between temperature and CO2 concentrations over the last 1000 years – as measured by Thompson’s team – is striking. Nonetheless the so-called global warming skeptics often say that global warming is really an illusion reflecting nature’s cyclical fluctuations. To support their view, they frequently refer to the Medieval Warm Period. But as Dr Thompson’s thermometer shows, the vaunted Medieval Warm Period (the third little red blip from the left below) was tiny in comparison to the enormous increases in temperature in the last half-century – the red peaks at the far right of the graph. These 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 graphic image representing the research of climate scientist Michael Mann and his colleagues. 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. (AIT, The Book)
[added] The transcript here (and I don’t vouch for the transcript) is a little different than the book, but clearly attributes the graphic here to oxygen isotope calculations from Lonnie Thompson:
The ice has a story to tell and it is worldwide. My friend Lonnie Thompson digs cores in the ice. They dig down and they bring the core drills back up and they look at the ice and they study it. When the snow falls it traps little bubbles of atmosphere. They can go in and measure how much CO2 was in the atmosphere the year that snow fell. What’s even more interesting I think is they can measure the different isotopes of oxygen and figure out the very precise thermometer and tell you what the temperature was the year that bubble was trapped in the snow as it fell.
When I was in Antarctica I saw cores like this and the guy looked at it. He said right here is where the US Congress passed the Clean Air Act. I couldn’t believe it but you can see the difference with the naked eye. Just a couple of years after that law was passed, it’s very clearly distinguishable.
They can count back year by year the same way a forester reads tree rings. You can see each annual layer from the melting and refreezing. They can go back in a lot of these mountain glaciers a thousand years. They constructed a thermometer of the temperature. The blue is cold and the red is warm. I show this for a couple of reasons. Number one the so called skeptics will sometimes say “Oh, this whole thing is cyclical phenomenon. There was a medieval warming period after all.” Well yeah there was. There it is right there. There are one there and two others. But compared to what is going on now, there is just no comparison. So if you look at a thousand years worth of temperature and compare it to a thousand years of CO2 you can see how closely they fit together. Now, a thousand years of CO2 data in the mountain glacier.
Readers yesterday observed the irony that the caption on Al Gore’s graphic was inverted with negative values at the top (something that was corrected in the book version.) I observed that I had examined Thompson’s ice core results and had been unable to identify any Thompson versions that corresponded to the Thompson graphic. It turns out that the Gore Hockey Stick has not derived from Thompson data at all; what it represents is a splicing of the MBH99 reconstruction (taken to 10-year averages) and a version of the CRU temperature history overlaid directly and merged with the MBH99 reconstruction. Thus the confirmation of MBH99 is ironically MBH99 itself.
Here is a closer view of Dr Thompson’s Thermometer. The Medieval Warm Period (not labeled in this version, but labeled in the book) is identified as occurring from about 1360-1370. In the DVD version, the y-axis is labeled incorrectly (it’s inverted), but the error is corrected in the book.
As noted yesterday, the Gore Hockey Stick appears to originate from a graphic in Thompson (Clim Chg 2003) which plots the CRU temperature history and MBH99 in the same figure, shown below (rotated to match the Gore version).
Thompson et al 2003. Figure 7d. The measured (Jones et al., 1999) and reconstructed (Mann et al., 1999) Northern Hemisphere temperatures are shown in (d) and are plotted as deviations (◦C) from their respective 1961’1990 means.
While this identification is very convincing, there are still some discrepancies when you actually try to replicate the exact Gore figure from MBH99 and CRU data. First here is a plot of MBH99 zeroed on 1961-1990 as stated in Thompson et al 2003 (Gore just says “Northern Hemisphere Temperature (◦C)”. Obviously this needs to be smoothed to match Gore.
In Thompson’s ice core articles, he usually/nearly always uses 10-year averages so this seemed like a logical smoothing strategy. Here’s the result – the shape matches very well, but it looks too “cold”. In the Gore graphic, there is at least something that is slightly above the zero-line, which he sarcastically refers to as the “Medieval Warm Period”, but there isn’t anything here.
The zero-period in MBH99 is 1902-1980, not 1961-1990. Perhaps Thompson only said that the data had been centered on 1961-90, but in fact, it was really left centered on 1902-1980. Here is a plot of MBH99 in 10-year averages centered on 1902-1980 and this looks like what is used. It’s a titch too “cold” – I’m not sure why.
Now let’s try to match the CRU version. I can probably forage around and find a 2000 vintage version that will match a little better, but for now I just used the HadCRU2 version presently online. First I tried it with 1960-1990 centering (as stated in Thompson), which would be somewhat inconsistent with the 1902-1980 centering of MBH99, but we’ve seen that before. My impression was that this is a little “cold”.
So I re-centered the CRU data on 1902-1980 to match MBH99 centering ( an adjustment of 0.156 deg C) and that seemed to work better. So it looks like both series are centered on 1902-1980.
Now to splice the two series. Here’s a plot which is more or less in Gore format: this seems to get most of the details. There are a few features that aren’t matched. The CRU version isn’t exactly right, though it’s very close. I could probably match it exactly with a bit more experimenting. In a case where the CRU temperature is warm, the Gore plot overwrites the MBH99 background and I’d have to experiment a little to replicate that graphic aspect. But you get the idea.
One thing that we can say for certain about the Gore graphic is that it completely merged the proxy and temperature records, making no effort whatever to distinguish them. I observed that Michael Mann had said at realclimate:
No researchers in this field have ever, to our knowledge, “grafted the thermometer record onto” any reconstruction. It is somewhat disappointing to find this specious claim (which we usually find originating from industry-funded climate disinformation websites) appearing in this forum.