D’Arrigo et al. [GRL 2004] reports on tree rings taken from the Seward Peninsula in northwestern Alaska from white spruce from 14 sites near elevational treeline in summer 2002. We show here their figures, demonstrating that the "proxy" show no evidence of the warm 1990s and hot 1998, raising questions about the ability of this type of commonly used proxy to pick up similar warm periods in the past.
The original study calculated site "chronologies" were calculated for both ring width and maximum density (MXD), but, contrary to AGU policy requiring data archiving for its publications (including GRL), d’Arrigo et al. have not archived their data.
The bottom panel of their Figure 3 below shows the ring width chronology through to 2002 (showing the same graph as in the preview). There is obviously no loud 1998 or loud 1990s.
They do not show the actual MXD site chronology. Instead, the top panel of their Figure 3 is a "temperature reconstruction" from the MXD chronology (and is presumably a linear transformation of the MXD chronology); thus the top panel can be construed as an image of the MXD chronology up to 1970 and has the the same features (in terms of maxima and minima) as the MXD chronology itself. Note the truncation at about 1970. This is explained as due to a "weakening" of the relationship between temperature and MXD.
Original Caption: Figure 3. Top line: May–August NTR extending from 1389–1970 (recent decades truncated, see text), based on 1909–1950 model. Thick lines shows smoothed values. Horizontal lines indicate mean values. Chronology based on 3 SP sites: Death Valley (65.19N, 162.27W, 239m), Alpine View (65.11N, 162.18W, 282m) and Hey Bear (65.22N, 162.22W, 229m) [D’Arrigo et al., submitted to Holocene, 2004]. Gray shading shows changing sample size over time, which ranges from 1–7 radii prior to 1640. Inferences of past climate prior to ca. 1640 should be interpreted with caution. Low value in 1783 is labeled. Middle line: May–August NAR [Jacoby et al., 1999]. Bottom line: SRW series [D’Arrigo et al., submitted to Holocene, 2004]. Vertical lines in SP records indicate acceptable EPS cutoff of 0.85 [Cook and Kairiukstis, 1990].
Their Figure 2 (shown below with original caption) appears to contain the information left out of their Figure 3. Here the dotted line presumably shows the shape of the MXD chronology in the period after 1980. As with the ring width chronology, there is no increase through the 1990s.
Original Caption. Figure 2. Actual (solid line) and estimated (dashed line) Nome May–August temperatures from 1909–2001 based on SP-MXD chronology, including both calibration (1909–1950) and verification (1951–1970) periods. Note that estimates after ca. 1970 tend to underpredict actual values (calibration ar2 declines from 42% for 1909–1950 to 38% for 1909–70 and 23.2% for 1909–2001). The ar2 for the verification period is 26%, with a positive RE of 0.20 in verification. Additional tests: calibration 1909–1920: ar2 67%, verification 1921–1950: RE = 0.31; calibration 1921–1950: ar2 38%; verification 1909–1920: RE = 0.40.
Reference: Rosanne D’Arrigo, Erika Mashig, David Frank, Gordon Jacoby, and Rob Wilson, 2004. Reconstructed warm season temperatures for Nome, Seward Peninsula, Alaska, GRL 31, L09202, doi:10.1029/2004GL019756.