Figure 14 – Comparison of GISP2 and Siple Dome ice core records with potential climate forcing factors. The GISP2 and Siple Dome Na and excess (xs) SO42- records (in ppb) were resampled to 5-year intervals (the lowest common resolution in both records is ~3 years). Two time periods discussed in the text are highlighted: 1680-1730 AD (period of coeval Na increase in Siple Dome and GISP2 records) and 1399-1427 AD (onset of LIA conditions). Two prominent volcanic events at 1815 AD (Tambora) and 1259 AD (possibly El Chichon) were used to confirm the Siple Dome annual layer counting and to correlate with the GISP2 record. The obvious xsSO42- increase during the last century in the GISP2 record, attributed to anthropogenic emissions (Mayewski et al., 1986), is notably absent from the Siple Dome and other Antarctic xsSO42- records . Other potential climate forcing factors include solar activity d14C residual series (Stuiver and Braziunas, 1989) and CO2 (the scale has been expanded to highlight LIA changes and does not include 20th century values) (Etheridge et al., 1996). Reprinted by permission from Kreutz et al., Science, 277, 1294-1296. © 1997, American Association for the Advancement of Science.