Correspondence Geology
November 2010 Vol.55 No.32: 3738–3740 doi: 10.1007/s11434-010-4137-9
SPECIAL TOPICS:
Reply to the comment of Cheng et al. ZHANG DeEr1*, LI Hong-Chun2, KU Teh-Lung3 & LU LongHua4 1
National Climate Center, Beijing 100081, China; Department of Earth Sciences, Cheng-Kung University, Tainan 70101, Taiwan, China; 3 Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089, USA; 4 Chinese Academy of Meteorological Sciences, Beijing 100081, China 2
Received April 27, 2010; accepted August 12, 2010
Citation:
Zhang D E, Li H-C, Ku T-L, et al. Reply to the comment of Cheng et al. Chinese Sci Bull, 2010, 55: 3738–3740, doi: 10.1007/s11434-010-4137-9
We thank Cheng et al. for their interest in our paper “On linking climate to Chinese dynastic change: Spatial and temporal variations of of monsoonal rain” [1]. Our paper was written largely as a response to the suggestion made by Zhang P Z, et al. [2] that climate has a key role in affecting chapters of Chinese cultural history (e.g. the demise of the Tang, Yuan and Ming dynasties). We are pleased to see that Cheng et al. are in general agreement with us in noting the spatial variability in monsoon rain and the regional disparity in the relationship between monsoonal intensity and rainfall in eastern China. In the same vein, no emphasis is placed by them on the “key role” of climate change in causing Chinese dynastic changes. Here, we clarify that while we do appreciate the fact that climate change can influence society and culture even in modern times, such influence is to be distinguished from affecting a dynastic change. The relationship between climate and Chinese dynastic change has been studied intensively by many historians. Our approach to this rather old and complicated problem was to use synoptic climatology. We demonstrated the spatial and temporal variations in monsoonal rain, and highlighted the potential severe uncertainty caused by using paleo-proxy records from a single locality in representing climate change over a broad area in inferring any link between climate and dynastic changes in ancient China [1]. Our caution “In considering climate as a vital factor affecting these activities in China including dynastic change, one should put this broad region into context unless cases to the contrary are specifically documented” reflects our objectivity *Corresponding author (email:
[email protected])
© Science China Press and Springer-Verlag Berlin Heidelberg 2010
towards such a complex problem. We emphasized that for an in-depth investigation of the issue using new types of records, each deduction and conclusion should be derived carefully. Presented in [2] and [3] are climate change records at 1- to 10-year scales revealed by newly-obtained high-resolution proxy data at a roughly annual timescale. Based on these records, we arrived at some new conclusions. We have no doubt on the high quality of the two records. However, from a meteorological perspective, it is questionable as to whether stalagmite or lake sediment records at a particular place can describe variations in the intensity of the East Asian Monsoon (EASM) on 1- to 10-a scales and in the precipitation of eastern China as a whole, or whether such records can serve as evidence of the important role played by the monsoon intensity change in the dynastic change in Chinese history. We therefore noted that “The conclusions drawn from both the Zhanjiang and Wudu records for monsoonal influence on dynastic changes are thus open to scrutiny as to their veracity” [1]. We think the crucial issue here is interpretation of the proxy data, and the extent to which the data allow the conclusions to be drawn. Cheng et al. [4] maintained that our major argument about the regional disparity in the EASM intensity–precipitation relationship is broadly consistent with their conclusions. It is not, and it is far from the truth. Our paper [1] was aimed at highlighting our disagreement with refs. [2] and [3] in their interpretation of the data. The disagreement in major viewpoints is there for all to see. The discrepancy arose from their assumption of a lock-step variation in rainfall for the whole of eastern China. They chose to ignore our observation that precipitation in North China (NC) and the csb.scichina.com
www.springerlink.com
ZHANG DeEr, et al.
Chinese Sci Bull
Jiang-Huai Drainage Basin (JH) responds in an opposite fashion to EASM strength changes: generally, a stronger EASM brings about increased precipitation in NC but decreased precipitation in JH. We examined the conclusions presented in refs. [2] and [3] against the spatial and temporal characteristics of precipitation over China using meteorological data, both instrumental and historical. We identified, as stated in paper [1], some misunderstanding of the precipitation properties in those conclusions, mainly because of an inadequate appreciation of the regional disparity as the cause of uncertainties therein. As examples, ref. [2] made use of a single-site stalagmite record in western China to represent precipitation change over eastern China as a whole, leading to inaccurate conclusions. Ref. [5] misused the curve of historical wetness condition in the Jiangnan area to denote variation in precipitation over the whole of eastern China. As pointed out previously [6], the precipitation change in Jiangnan region differs greatly from that across eastern China. Cheng et al. considered that our approach “lacks logical vigor”. This is certainly a sweeping statement as our arguments were developed clearly, step-by-step, under four sub-titles. They further challenged “the assumption that the variability in the monsoon in earlier times was the same as in the past 50 years” on the account that “global warming and anthropogenic impacts on climate (including monsoonal system) could well have caused anomalous climatic conditions in the past 50 years” [4]. We have not read any report which invalidates the theories of monsoonal dynamic meteorology or synoptic climatology. In fact, the statistical relationship between monsoon intensity and precipitation in recent times can be expounded using the theory of synoptic-climatology. Therefore, there is no reason to prevent such a relationship being applied to ancient times. It should be pointed out that in paper [2] the authors also interpreted their 2000-year δ18O record in terms of past wetness changes using local meteorological data and monsoon indices for the past 50 years. While we agree that the relationship can be more rigorously tested by re-calculation using a variety of methods, which will be given in another paper, we maintain that on a time scale of 1–10 a, it would be difficult to accept the Wudu and Zhanjiang records as representative of a large part of China. There is a pressing need to clarify the relation between monsoon intensity and rainfall at different timescales. We have pointed out [1] that the interrelation between summer rainfall and intensity of EASM is not a simple linear one. In this regard, some of the concepts on the monsoon system and the account of the relationship between monsoonal intensity and precipitation advanced by Cheng et al. [4] appear vague and offer few insights. They diverge greatly from the basic principles of synoptic climatology and if used to discuss the monsoonal intensity-rainfall relation, would inevitably run the risk of leading to biased conclusions. As pointed out rightly in the comment, uncertainties in-
November (2010) Vol.55 No.32
3739
herent in a time series of quantitative climate proxies, including historical dry/wet indices (DWI), speleothem δ18O and lake sediment Ti content, cannot be ignored. We have made an effort to diminish possible effects of subjective factors by comparing sequences of dryness/wetness indices of Chinese historical climate produced independently by two research groups [1]. We agree that calibration of the proxy climate records including historical climate records remains a fundamental research focus, which is the topic of our on-going project [7]. As is commonly known, there was a multitude of evidence of riots and unrest because of extreme droughts in Chinese history which historians have studied intensively. One event deserves particular attention, which was the extreme drought of AD 875. Although this drought caused the peasant riot led by Huang Chao, the Tang Dynasty did not end until 30 years after the riot, and during these 30 years there were plentiful rains. Cheng et al. quoted but misinterpreted our statement about the fall of two dynasties, the Northern Song and Qing dynasties, at the times of ⑥ and ⑦ in Figure 1 of our paper [1]. We considered ⑥ and ⑦ to be at the peaks of the stalagmite curve (implying strong monsoon occurrence) rather than in the period of “no significant monsoon anomalies’ [4] Our observation is not consistent with the original ideas of ref. [2]. Rather, it illustrates countering examples to those statements of ref. [2]. Cheng et al. gave many examples based on other materials including folk songs and the Grand Canal to illustrate the relationship between monsoon intensity and social development. We choose not to make comments on such an approach in view of the abundance of Chinese historical materials, whereby to continue the listing of scattered, anecdotal examples would lead to an increase in opposing views. In any case, the comments by Cheng et al. failed to negate our observation that the stalagmite-based strong (weak) monsoon corresponds to social stability as well as upheaval for periods ① to ④ (⑤ to ⑦) presented in Figure 1 of our paper [1]. Our statement that the “period of heavy and light δ18O values in the Wanxiang Cave record may relate to times of either social stability or turmoil in Chinese history, defying meaningful correlations” remains valid [1]. We would like to point out another example of misrepresenting our position by their statement: “Zhang et al. suggest that because not all cultural changes are obviously affected by climate, none of them are [4].” No such suggestion was ever made in our paper [1]. We stress again that the main conclusion of our study is that strong spatial variations in rainfall render regional disparity between rainfall and EASM intensity over eastern China, and that to interpret Chinese cultural and political history based on paleo-proxy records of drought/wetness from a single locality should be done with great care. Finally, we were surprised and disappointed to see Cheng
3740
ZHANG DeEr, et al.
Chinese Sci Bull
et al. citing a statement made by one of us (ZD) from an earlier publication and insinuating its political overtone. The statement which questioned the validity of attributing Chinese dynastic collapses to a single natural factor such as precipitation irregularities on a decadal scale, was made in a different context. It is inapplicable to the paper of interest [1]. We believe that the citation and its related “political implications” narrative [4] do not belong in a scientific discussion such as this one. This work was supported by the China Global Change Research Program (2010CB950103).
November (2010) Vol.55 No.32
2
3
4
5
6 7
1
Zhang D E, Li H C, Ku T L, et al. On linking climate to Chinese dy-
nastic change: Spatial and temporal variations of monsoonal rain. Chinese Sci Bull, 2010, 55: 77–83 Zhang P Z, Cheng H, Edwards R L, et al. A test of climate, sun and culture relationships from an 1810-year Chinese cave record. Science, 2008, 322: 940–942 Yancheva G, Nowaczyk N R, Mingram J, et al. Influence of the intertropical convergence zone on the East-Asian monsoon. Nature, 2007, 445: 74–77 Cheng H, Edward R L, Haug G H. Comment on “On linking climate to Chinese dynastic change: Spatial and temporal variations of monsoonal rain”. Chinese Sci Bull, 2010, 55: 3734–3737 Yancheva G, Nowaczyk N R, Mingram J, et al. Replying to De’er Zhang & Longhua Lu Nature 450, doi: 10.1038/nature06338. Nature, 2007, 450: E8–E9 Zhang D E, Lu L H. Anti-correlation of summer and winter monsoons? Nature, 2007, 450, E7–E8 Zhang D E. Test of calibration on the paleoclimatic proxy data using Chinese historical records (in Chinese). Adv Clim Change Res, 2010, 6: 70–72
