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Timing, Duration, and Transitions of the Last Interglacial Asian Monsoon

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Timing, Duration, and Transitions of the Last Interglacial Asian Monsoon R EPORTS 24. C. E. Forest, P. H. Stone, A. P. Sokolov, M. R. Allen, M. damage function indicated above that produces a ways for non-CO2 gases and for other anthropogenic D. Webster, Science 295, 113 (2001). ϳ45% reduction in the probability of DAI[50‰] with a radiative forcing agents such as aerosols would also 25. Transient temperature change in 2100 is not, in 0% PRTP produces a reduction of only ϳ10% and an affect the potential for DAI. general, equilibrium change. The inertia of the cli- order of magnitude lower “optimal” carbon tax when 29. R. J. Lempert, M. E. Schlesinger, Clim. Change 45, 387 mate system is such that climate change will contin- we used a 3% PRTP, the value employed by the original (2000). ue long after greenhouse gas concentrations are sta- DICE model. We chose to use a 0% PRTP for Fig. 3 30. T. Wigley, Clim. Change, in press. bilized or emissions eliminated. Some outcomes that exactly for this reason—that using a high discount rate 31. C. Azar, H. Rodhe, Science 276, 1818 (1997). avoid exceeding a DAI threshold until 2100 will ex- masks the variation in model results because of changes 32. B. C. O’Neill, M. Oppenheimer, Science 296, 1971 ceed that threshold in the next century. Therefore, in parameters other than the discount rate, and observ- (2002). the time horizon of analysis will affect the potential ing variation in model results due to other parameters is 33. We thank T. Wigley, K. Kuntz-Duriseti, J. Bushinsky, for DAI. However, what is “dangerous” is itself a central to our analysis. and M. Hayes for constructive comments on previous function of adaptive capacity, not a static quantity, 28. We consider three of these sources of uncertainty in the drafts. Supported by the Global Change Education dependent on social and economic development. So, three parameters we varied, but there are other impor- Program of the Department of Energy and the Inter- the very threshold for any percentile X, DAI[X‰], can tant sources of uncertainty. The DICE model does not disciplinary Graduate Program in Environment and itself change with time and social conditions. consider adaptation, as opposed to mitigation, which Resources at Stanford University (M.D.M.) and by the 26. In the DICE model, carbon taxes serve as a proxy for theoretically would shift the probability distribution for Winslow Foundation (S.H.S.). general climate policy controls. Thus, we do not DAI to higher temperature levels. A highly adaptive present carbon tax data as a preferred method for society would be less likely to experience dangerous Supporting Online Material mitigation or a required method to produce our impacts, although this would not be as likely to apply to www.sciencemag.org/cgi/content/full/304/5670/571/ results. Instead, these results should be seen as a the first reason for concern, damages to natural sys- DC1 method to provide insights into coupled model be- tems. The DICE model also only considers mitigation Materials and Methods havior, using the carbon tax in DICE as a measure of policies for CO2. It does not account for “knock-on” Fig. S1 the magnitude of climate policy controls. impacts of CO2 reductions on emissions of other atmo- References and Notes 27. Results such as this are extremely sensitive to the spheric substances, and it specifies a fixed path for discount rate. For example, the increase in the climate non-CO2 greenhouse gases. Alternative emissions path- 1 December 2003; accepted 19 March 2004 119°10ЈE; elevation 100 m; cave tempera- Timing, Duration, and ture 15.7°C; mean annual precipitation ␦18 ϭ OVSMOW –8.4 per mil (‰) (VSMOW, Transitions of the Last Vienna standard mean ocean water); and mean annual precipitation 1036 mm] (table Interglacial Asian Monsoon S1), covering the last glacial period [75 ka to 10 thousand years (ky) before the Daoxian Yuan,1 Hai Cheng,2 R. Lawrence Edwards,2* present]. We now report similar data from Carolyn A. Dykoski,2 Megan J. Kelly,2 Meiliang Zhang,1 Dongge Cave, China, 1200 km WSW of Jiaming Qing,1 Yushi Lin,1 Yongjin Wang,3 Jiangyin Wu,3 Hulu Cave, a site affected by the Asian 4 5 5 Monsoon. The Dongge record more than Jeffery A. Dorale, Zhisheng An, Yanjun Cai doubles the time range covered in the Hulu record and overlaps the Hulu record for Thorium-230 ages and oxygen isotope ratios of stalagmites from Dongge Cave, ϳ35 ky, allowing comparison between China, characterize the Asian Monsoon and low-latitude precipitation over the sites. Highlights include the timing and past 160,000 years. Numerous abrupt changes in 18O/16O values result from rapidity of the onset (4) and end of the Last changes in tropical and subtropical precipitation driven by insolation and mil- Interglacial Asian Monsoon and the degree lennial-scale circulation shifts. The Last Interglacial Monsoon lasted 9.7 Ϯ 1.1 of Last Interglacial Monsoon variability. thousand years, beginning with an abrupt (less than 200 years) drop in 18O/16O Dongge Cave is 18 km SE of Libo, values 129.3 Ϯ 0.9 thousand years ago and ending with an abrupt (less than Guizhou Province (25°17ЈN, 108°5ЈE), at an 300 years) rise in 18O/16O values 119.6 Ϯ 0.6 thousand years ago. The start elevation of 680 m. The cave temperature coincides with insolation rise and measures of full interglacial conditions, (15.6°C), mean annual ␦18O of precipitation indicating that insolation triggered the final rise to full interglacial conditions. (–8.3‰), and seasonal changes in precipita- tion and ␦18O of precipitation are similar to The characterization of past climate is often Although many such records are bench- those at Hulu, with mean annual precipitation limited by the temporal resolution, geo- marks, they are limited to high-latitude or being higher (1753 mm) (table S1). Stalag- graphic coverage, age precision and accu- high-elevation sites, which record the oxy- mites D3 and D4 were collected ϳ100 m racy, and length and continuity of available gen isotopic composition of the last frac- below the surface, 300 and 500 m from the records. Among the most robust are ice tion of atmospheric moisture remaining af- entrance, in the 1100-m-long main passage- core records (1, 2), which characterize, ter transit from moisture source regions. way. D3 is 210 cm and D4 is 304 cm long, among other measures of climate, the oxy- Cave calcite also contains information with the diameters of each varying between gen isotopic composition of precipitation. about the isotopic composition of meteoric 12 and 20 cm. Stalagmites were halved ver- precipitation, is widespread, and can be tically and drilled along growth axes to pro- dated with 230Th methods. Thus, caves may duce subsamples for oxygen isotope analysis 1Karst Dynamics Laboratory, Ministry of Land and yield well-dated, low-latitude, low-eleva- (5) and 230Th dating by thermal ionization (6, Resources, 40 Qixing Road, Guilin 541004, China. 2Department of Geology and Geophysics, University tion records that characterize atmospheric 7) and inductively coupled plasma mass spec- 230 of Minnesota, Twin Cities, MN 55455, USA. 3College moisture earlier in its transit from source troscopy (8). Sixty-six Th dates from D3 of Geography Science, Nanjing Normal University, regions. We report here on such a record of and D4 (table S2) and 10 dates from Hulu Nanjing 210097, China. 4Department of Geoscience, Asian Monsoon precipitation, which covers Cave stalagmite H82 (table S3), all in strati- 5 University of Iowa, Iowa City, IA 52242, USA. State most times since the penultimate glacial graphic order, have 2␴ analytical errors of Key Lab of Loess and Quaternary Geology, Institute of Ϯ Ϯ Earth Environment, Chinese Academy of Sciences, period, about 160 thousand years ago (ka). 80 years at 10 ky and 1 ky at 120 ky. Six Xi’an 710075, China. We have previously reported a cave oxy- hundred and forty ␦18O measurements have *To whom correspondence should be addressed. E- gen isotope record of the East Asian Mon- spatial resolution corresponding to 20 years mail: [email protected] soon (3) from Hulu Cave, China [32°30ЈN, to 2 ky for different portions of D3 and D4 www.sciencemag.org SCIENCE VOL 304 23 APRIL 2004 575 R EPORTS (Dongge Cave, table S4), and 830 ␦18O mea- that the ␦18O values are not strongly affected raneous deposition of D4 and the Hulu Cave surements on H82 have average spatial by water/rock interactions or kinetic fraction- stalagmites (ϳ35 ky), the caves’ records rep- resolution corresponding to 7 years (Hulu ation (9, 10). Although we have not yet iden- licate remarkably well (Figs. 1 and 2), indi- Cave, table S5). tified young calcite from Hulu, D4’s young- cating not only that the calcite ␦18O can A key issue is whether stalagmite ␦18O est calcite (Fig. 2) was deposited in isotopic largely be interpreted in terms of the ␦18Oof values (Figs. 1 and 2) can be interpreted equilibrium, because its ␦18O value, the mean meteoric precipitation and cave temperature, solely in terms of the ␦18O of precipitation annual ␦18O of modern meteoric precipita- but also that the two sites have a similar and cave temperature. The general replication tion, and mean annual temperature (table S1) history of meteoric ␦18O and cave tempera- (3)of␦18O values for 35 ky of contempora- satisfy the equilibrium calcite/water fraction- ture. Because Dongge is 1200 km from Hulu, neous growth, for D3 and D4 (Fig. 2), argues ation equation (11). For times of contempo- this generalizes the Hulu results to areas well to the southwest. Indeed, the broad trends in the Dongge/Hulu data have similarities with Fig.
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