What was done
The authors say they "established an annual layer thickness chronology (LTC) for stalagmite TS9501 from Beijing Shihua Cave and reconstructed a 2650-year (BC 665-AD 1985) warm season (MJJA: May, June, July, August) temperature record (WTR) for Beijing by calibrating the LTC with the observed MJJA temperature record (Tan et al., 2003)."

What was learned
Tan et al. (2004) report that their warm season temperature record "is consistent with oscillations in total solar irradiance inferred from cosmogenic ¹⁰Be and ¹⁴C," and that it also "is remarkably consistent with Northern Atlantic drift ice cycles that were identified to be controlled by the sun through the entire Holocene [Bond et al., 2001]."  Going backwards in time, both records clearly depict the start of the Modern Warm Period, the prior Little Ice Age, the Medieval Warm Period, the Dark Ages Cold Period, the Roman Warm Period, and the cold climate at the start of both records.

What it means
The authors conclude that "the synchronism between the two independent sun-linked climate records therefore suggests that the sun may directly couple hemispherical climate changes on centennial to millennial scales."  In addition, the cyclical nature of the millennial-scale oscillation of climate that is evident in both climate records further suggests there is no need to invoke rising atmospheric CO2 concentrations as a cause of the development of the Modern Warm Period.

References
Bond, G., Kromer, B., Beer, J., Muscheler, R., Evans, M.N., Showers, W., Hoffmann, S., Lotti-Bond, R., Hajdas, I. and Bonani, G.  2001.  Persistent solar influence on North Atlantic climate during the Holocene.  Science 294: 2130-2136.

Tan, M., Liu, T.S., Hou, J. Qin, X., Zhang, H. and Li, T.  2003.  Cyclic rapid warming on centennial-scale revealed by a 2650-year stalagmite record of warm season temperature.  Geophysical Research Letters 30: 10.1029/2003GL017352.