Climate Audit

Now that I’ve caught my breath a little, just for fun, I’m parsing through sections of the NAS report on areas not directly involving the MM-MBH battle. In the press conference, I recall Cuffey placing a lot of emphasis on the "regional" MWP, and that it wasn’t in the Antarctic ice core data (although it was in Greenland data.) Maybe someone can give a time and reference for what he said and I’ll edit up. In the summary, the panel stated:

This [additional] evidence [of the unique nature of recent warmth in the context of the last one or two millennia] includes …the fact that ice cores from both Greenland and coastal Antarctica show evidence of 20th century warming (whereas only Greenland shows warming during medieval times).

In the Ice Core chapter (preprint p. 62), they said:

Some coastal sites in Antarctica show 20th century warming but interior sites do not. No Antarctic sites show a warming during medieval times.

Now I don’t claim to be an authority on ice cores, but here’s the Law Dome dO18 series as illustrated in Jones and Mann 2004, which has a very strong maximum at AD1000, exactly the same time of very active Viking exploration in Greenland. It also has minimal 20th century warming. Isn’t this the exact opposite of the situation as summarized?

Figure 4. Jones and Mann 2004.

The NAS panel does not actually illustrate or cite any series with the said property: modern warming and no medieval warming. Elsewhere in the NAS report, the panel says:

"In Greenland, Figure 6-2, and coastal Antarctica, ice isotopic ratio records clearly show 20th century warming, a Little Ice Age and earlier warmth. In Greenland, this earlier warmth is centered at about AD1000, whereas in Antarctica, it is much earlier … As a group, the ice cores from interior Antarctica (Figure 6-2) show nothing anomalous about the 20th century warming".

They don’t cite the series that are considering here. To the extent that the Law Dome series is representative, the high dO18 period is mostly dated prior to AD1000, but the actual peak is at AD1000. (I also wonder how much play there is in the dating, but that’s a different story.)

In their figure, they illustrated Taylor Dome from interior Antarctica: here is the bottom panel of Figure 6-2 showing information from Taylor Dome – curiously they show dD values rather than dO18 (shown for the other sites) , even though dO18 is available for Taylor Dome. Yes, there is no MWP in Taylor Dome series (and presumably other interior sites), but according to the graph of Taylor Dome (and the NAS text), there is no modern warming reflected in this data either.

NAS Figure 6.2 Bottom Panel. Taylor Dome dD

A comment from Fisher about Greenland Summit gives one theory why there might be less variability at some of the coldest, most remote sites. Fisher noted that the dO18 at Greenland summit did not show marked modern warming or MWP and mooted the possibility that some very remote and very, very cold sites might have little response to lesser changes (think of a LIFO inventory management system) . Maybe this hypothesis applies to the Antarctic interior as well. In the literature, there are suggestions that centennial warming tends to be through poleward movement of mid-latitude systems, with strengthening of polar vortices. Thus mid-latitude warming characteristic of centennial changes might not have a strong impact on the coldest and most remote sites in interior Antarctica.

So what’s the basis for the statements in the summary and for Cuffey’s statements at the press conference? Whatever it is, I can’t find it in the details of the report.