Xu, H., Hong, Y., Lin, Q., Zhu, Y., Hong, B. and Jiang, H. 2006. Temperature responses to quasi-100-yr solar variability during the past 6000 years based on δ18O of peat cellulose in Hongyuan, eastern Qinghai-Tibet plateau, China. Palaeogeography, Palaeoclimatology, Palaeoecology 230: 155-164.
What was done
The authors compared temperature variations inferred from δ18O in peat cellulose found at Hongyuan (32°46'N, 102°30'E), which were obtained by Xu et al. (2002) on the eastern Qinghai-Tibet Plateau of southwestern China, with solar activity inferred from atmospheric 14C and 10Be concentrations measured in a South Pole ice core, after which they performed cross-spectral analyses to determine the relationship between temperature and solar variability, comparing their results with similar results obtained by Hong et al. (2000) for peat found 2400 km away at Jinchuan, China (42°20'N, 126°22'E), as well as with the findings of other researchers around the world who have studied solar-climate relationships.
What was learned
Xu et al. report that "during the past 6000 years, temperature variations in China exhibit high synchrony among different regions, and importantly, are in-phase with those discovered in other regions in the northern hemisphere." They also say that their "comparisons between temperature variations and solar activities indicate that both temperature trends on centennial/millennial timescales and climatic events are related to solar variability."
What it means
The researchers' final conclusion was that "quasi-100-year fluctuations of solar activity may be the primary driving force of temperature during the past 6000 years in China." And since their data indicate that peak Medieval Warm Period temperatures were higher than those of the recent past, it is not unreasonable to assume that the planet's recent warmth may have been solar-induced as well.
Hong, Y.T., Jiang, H.B., Liu, T.S., Zhou, L.P., Beer, J., Li, H.D., Leng, X.T., Hong, B. and Qin, X.G. 2000. Response of climate to solar forcing recorded in a 6000-year δ18O time-series of Chinese peat cellulose. The Holocene 10: 1-7.
Xu, H., Hong, Y.T., Lin, Q.H., Hong, B., Jiang, H.B. and Zhu, Y.X. 2002. Temperatures in the past 6000 years inferred from δ18O of peat cellulose from Hongyuan, China. Chinese Science Bulletin 47: 1578-1584.Reviewed 4 October 2006