Thursday, March 13, 2014

New paper finds droughts in China were more severe in the past when CO2 was "safe"

A paper published today in Climate of the Past reconstructs climate over the past 306 years in SE China and finds precipitation extremes were much more severe in the past when CO2 was "safe." According to the authors, the longest drought occurred from 1867-1932, the longest wet period occurred from 1934-1957, and the 19th century was the driest century. The authors find, "recent drought in 1993–2008 was still within the frame of natural climate variability based on the 306 yr PDSI reconstruction."

The authors also find precipitation was strongly linked to solar activity and the natural Asian-Pacific Oscillation [APO]. The tree-ring reconstruction also shows another non-hockey-stick with temperatures in the 1940's and 1650's higher than at the end of the record in 2008.

Reconstruction of the Palmer Drought Severity Index [PDSI] shows there is nothing unusual, unnatural, or unprecedented with regard to 20th century drought 

Top graph of tree ring index shows another non-hockey-stick

Clim. Past, 10, 509-521, 2014

Q. Cai1, Y. Liu1,2, Y. Lei1, G. Bao3, and B. Sun4
1The state key laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, 710075, China
2Department of Environmental Science and Technology, School of Human Settlements and Civil Engineering, Xi'an Jiaotong University, Xi'an, 710049, China
3Key Laboratory of Disaster Monitoring and Mechanism Simulating of Shaanxi Province, Baoji University of Arts and Sciences, Baoji, 721013, Shaanxi, China
4Department of Resources, Environment, and Urban Sciences, Xianyang Normal University, Xianyang, 712000, China

Abstract. We utilised tree-ring cores, collected from three sites at Lingkong Mountain located in the southeast part of the Chinese Loess Plateau (CLP), to develope a regional ring-width chronology. Significant positive correlations between the tree-ring index and the monthly Palmer drought severity index (PDSI) were identified, indicating that the radial growth of trees in this region was moisture-limited. The March–August mean PDSI was quantitatively reconstructed from 1703 to 2008 with an explained variance of 46.4%. Seven dry periods during 1719–1726, 1742–1748, 1771–1778, 1807–1818, 1832–1848, 1867–1932 and 1993–2008 and six wet periods during 1727–1741, 1751–1757, 1779–1787, 1797–1805, 1853–1864 and 1934–1957 were revealed in our reconstruction. Among them, 1867–1932 and 1934–1957 were identified as the longest dry and wet periods, respectively. On the centennial scale, the 19th century was recognised as the driest century. The drying tendency since 1960s was evident. However, recent drought in 1993–2008 was still within the frame of natural climate variability based on the 306 yr PDSI reconstruction. The dry and wet phases of Lingkong Mountain were in accordance with changes in the summer Asian-Pacific oscillation (IAPO) and sunspot numbers, they also showed strong similarity to other tree-ring based moisture indexes in large areas in and around the CLP, indicating the moisture variability in the CLP was almost synchronous and closely related with large-scale land–ocean–atmospheric circulation and solar activity. Spatial correlation analysis suggested that this PDSI reconstruction could represent the moisture variations for most parts of the CLP, and even larger area of northern China and east Mongolia. Multi-taper spectral analysis revealed significant cycles at the inter-annual (2–7 yr), inter-decadal (37.9 yr) and centennial (102 yr) scales. Results of this study are very helpful for us to improve the knowledge of past climate change in the CLP and enable us to prevent and manage future natural disasters.

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