August temperature variability in the southeastern Tibetan Plateau since AD 1385 inferred from tree rings

Zhu, H.F., et al., August temperature variability in the southeastern Tibetan Plateau since AD 1385 inferred from tree rings. Palaeogeography, Palaeoclimatology, Palaeoecology, 2011: p. doi:10.1016/j.palaeo.2011.02.017.

Long-term high-resolution climate proxies are essential for understanding climate variability on the Tibetan Plateau (TP), where few long-term climate records are available. We developed a new summer (August) temperature reconstruction over the period 1385-2002 based on a tree-ring width chronology of Balfour spruce (Picea likiangensis var. balfouriana) on the southeastern TP created using the Regional Curve Standardization method. The reconstruction explains 44.7% of the variance in the instrumental temperature records during the calibration period (1962-2002), and captures temperature variability over a broad region of the TP. Warmer than average Augusts were found during the periods 1446-1494, 1509-1522, 1553-1567, 1797-1812, 1845-1905 and 1918-2002. Cooler than average Augusts occurred from 1385-1416, 1426-1445, 1495-1508, 1523-1552, 1568-1686, 1695-1718, 1725-1796, 1813-1844 and 1906-1917. A warming trend in the 20th century was unprecedented during the past six centuries. The reconstruction closely matched other tree-ring summer temperature reconstructions from neighboring regions, as well as patterns from ice-core δO18 data, and fluctuated in synchrony with Northern Hemisphertemperature reconstructions.

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Millennial temperature reconstruction based on tree-ring widths of Qilian juniper from Wulan, Qinghai Province, China

The climate of the past 1000 years is an important context for evaluating the recent climate warming. However, there are few 1000-year-long climate reconstructions with annual resolution in the Qinghai-Tibet Plateau. In this paper, a dendroclimatic analysis was conducted for the radial growth of Qilian juniper from the upper forest limit in Wulan, Qinghai Province. The results of correlation analysis between the tree-ring widths and the climate variables indicate that the growth of junipers at the upper forest limit is mainly limited by low temperatures of September, November and February of the pre-growth season, and July of the current growth season. There is no significant correlation between the tree-ring widths and precipitation. A mean temperature from the previous year’s September to the current year’s April was reconstructed for the Wulan area since A.D. 1000. The reconstruction can explain 40.8% of the instrumental variance in the calibration period (1856―2002). The reconstruction shows that the 20th century is the warmest 100 years, and the 1990s is the warmest decade during the past 1000 years, while the coldest 100 years and decade occur at 1600―1699 and 1642―1651, respectively. The variations are verified well by the temperature reconstruction of the middle Qilian Mountain (QL) and the total organic carbon (TOC) in the Qinghai Lake sediments. The comparison of our reconstruction with the annual temperature reconstruction of extra-tropical Northern Hemisphere suggests that the climate of Wulan during the Medieval Warm Period is of obvious regional specialty, but there was a good response to the climate of hemispheric scales during the recent 400 years.

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