Guest post by Dr. J Storrs Hall

A bit over a year ago, in the wake of Climategate, I put up a blog post over at the Foresight Institute which got picked up and run here at WUWT. The essence of the post was that there was lots of natural variation in the ice core record of climate, so that it was reasonable to be skeptical of scientists who claimed that recent CO2 variations were “the only thing that could account for the recent warming trend” (quoting myself).

Apparently that got enough exposure — and was persuasive enough — that over a year later the alarmists still feel the urge to “debunk” it. Most recently, Rob Honeycutt at the “SkepticalScience” alarmist fanboi blog weighed in with this: Crux of a Core, Part 1 – addressing J Storrs Hall. Now the thing about this particular piece that jumped out at me at first was the fact that he associated me with a graph I never used, and he calls me “Mr. Hall” to make me sound less qualified than other sources such as “Dr. Alley” he refers to. It’s Dr. Hall (and yes, I am a scientist, not a nanotech engineer as he claims), a fact that he could have discovered in 3 seconds with Google. That told me about all I needed to know about Honeycutt’s bona fides (in the original Latin sense of acting in good faith).

The only substantive point in the post is that GISP2 (or any specific ice core) is a local as opposed to global temperature record. Is it misrepresentation to use it as a proxy for global climate? Well, the inconvenient truth is that I’m hardly the first person to use ice cores as climate proxies in popular presentations:

… but, on the other hand, it’s actually an interesting question and one worth looking at.

How Ice Cores Record a History of Climate

That’s not my title, it’s from this page at the GISP2 site. Not “a history of local temperature,” — of climate. Here are some quotes from the abstracts of papers by GISP2 authors:

“Ice cores provide high-resolution, multi-parameter records of changes in climate and environmental conditions spanning two or more full glacial- interglacial cycles. …”

“Polar ice contains a unique record of past climate variations; …”

“One of the most dramatic climate events observed in marine and ice core records is the Younger Dryas (YD), … High resolution, continuous glaciochemical records, newly retrieved from central Greenland, record the chemical composition of the Arctic atmosphere at this time. This record shows that both onset and termination of the YD occurred within 10-20 years …”

“The Greenland Ice Sheet Project 2 (GISP2) core can enhance our understanding of the relationship between parameters measured in the ice in central Greenland and variability in the ocean, atmosphere, and cryosphere of the North Atlantic Ocean and adjacent land masses. …”

“High-resolution, continuous multivariate chemical records from a central Greenland ice core provide a sensitive measure of climate change…”

“The accumulation record from the GISP2 core as an indicator of climate change throughout the Holocene” (paper title)

So, sure, a single ice core is not a global average temperature record; but it is quite a bit more than one thermometer. It’s just mud-slinging to claim that using it for a climate proxy is “misinformation”.

… especially when I didn’t just use one ice core in my post but two, and the other one was from Antarctica. One way to cut past the verbiage is simply to look at a comparison of the Greenland and Antarctic data and see how well they correlate:

(This is GISP2 in green, NGRIP, another Greenland core, in cyan, and the Vostok Antarctic core in blue. The Vostok has been scaled and shifted for a best match with the others; the temperature in Antarctica is colder, with smaller variations, than in Greenland. Furthermore, there are some time-scaling issues — note the temporal divergence of the two Greenland records before about 40 kya. It’s possible that NH/SH actually match better than this plot indicates. Look here for data.)

Nowhere near a perfect match, but it’s pretty clear that these are all from the same planet. Even Vostok shows the Younger Dryas, which is generally believed to be a mostly northern-hemisphere event. The NH has more variability in ice ages, notably the Dansgaard-Oeschger events, but the SH more, on a relative scale, in the Holocene.

The GISP2 people also compared their core’s record with Antarctic ones; on this page they say that it “shows close correlation between GISP2 and Vostok in the delta 18O of air in these ice cores.” (That’s a key temperature proxy.) On this page they say “Holocene climate is characterized by rapid climate change events and considerable complexity. GISP2 Holocene ¶18O (proxy for temperature) (Grootes, et al., 1993) and EOF1 (composite measure of major chemistry representing atmospheric circulation) show parallel behavior for the Early Holocene but not for the Late Holocene (O’Brien, et al., 1995).”

Note that bit about “rapid climate change events.” In the words of Jeffrey Masters here, “The historical records shows us that abrupt climate change is not only possible–it is the normal state of affairs. The present warm, stable climate is a rare anomaly.” (And he’s talking specifically about the lessons of GISP2 — although alas he takes home the wrong lesson from it.) See also this recent post here by Don Easterbrook.

Does GISP2 — or any other paleoclimate record — show us that climate change isn’t happening? No, of course not. It shows us that climate change always happens. The 20th-century warming was hardly unprecedented, and doesn’t call for unusual explanations.

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