Der Monsun ist für China von größter Bedeutung. Das Geesthachter Helmholtz-Zentrum schreibt hierzu auf seinem wiki Bildungsserver Klimawandel:
In vielen Monsungebieten ist die Landwirtschaft daher in hohem Maße von den sommerlichen Monsun-Niederschlägen abhängig. Auch für den Anbau in der Nachmonsunzeit (ab November auf der Nordhalbkugel) sind die vorausgegangenen Monsunniederschläge wichtig, da bei reichlichen Niederschlägen Bodenfeuchte und Grundwasserspeicher hoch sind, was den Winterpflanzen zugute kommt bzw. der Bewässerung dient. Es gibt weltweit keine Klimaschwankung, die einen größeren Einfluss auf die Gesellschaft hat, als die Veränderungen des Monsun-Niederschlags, der die Lebensader von Zweidritteln der Weltbevölkerung darstellt.Insbesondere gilt das für Indien und China mit ihren sehr hohen Bevölkerungsdichten in den Monsungebieten. Veränderungen der Monsunzirkulation durch den Klimawandel sind daher von größter Bedeutung für einen erheblichen Teil der Weltbevölkerung.
Paläoklimatologische Untersuchungen konnten eine sehr starke natürliche Variabilität des Asiatischen Monsuns dokumentieren. Es ist daher von größter Bedeutung, zunächst die natürliche Schwankungsbreite und den Antrieb der Veränderungen zu verstehen, bevor über anthropogene Einflüsse spekuliert wird. China hat dies bereits erkannt und eine ganze Reihe von Studien initiiert, die die Monsunvariabilität der letzten 10.000 Jahre zum Thema hatten. Interessanterweise finden fast alle Studien, dass die Stärke des Monsuns maßgeblich von der Sonnenaktivität beeinflusst wird.
Im Oktober 2014 veröffentlichten Yin et al. in Climate of the Past eine Arbeit auf Basis von Untersuchungen von Höhlen-Tropfsteinen aus Zentralchina. Sie fanden, dass der Monsun während extremer solarer Schwächephasen wie dem Maunder Minimum ausblieb und sich Dürren entwickelten. Auch die Temperaturen zeigten einen engen Bezug zur Sonnenaktivität. Hier der Abstract:
Variation in the Asian monsoon intensity and dry–wet conditions since the Little Ice Age in central China revealed by an aragonite stalagmite
This paper focuses on the climate variability in central China since AD 1300, involving:
(1) a well-dated, 1.5-year resolution stalagmite δ18O record from Lianhua Cave, central China
(2) links of the δ18O record with regional dry–wet conditions, monsoon intensity, and temperature over eastern China
(3) correlations among drought events in the Lianhua record, solar irradiation, and ENSO (El Niño–Southern Oscillation) variation.
We present a highly precise, 230Th / U-dated, 1.5-year resolution δ18O record of an aragonite stalagmite (LHD1) collected from Lianhua Cave in the Wuling Mountain area of central China. The comparison of the δ18O record with the local instrumental record and historical documents indicates that (1) the stalagmite δ18O record reveals variations in the summer monsoon intensity and dry–wet conditions in the Wuling Mountain area. (2) A stronger East Asian summer monsoon (EASM) enhances the tropical monsoon trough controlled by ITCZ (Intertropical Convergence Zone), which produces higher spring quarter rainfall and isotopically light monsoonal moisture in the central China. (3) The summer quarter/spring quarter rainfall ratio in central China can be a potential indicator of the EASM strength: a lower ratio corresponds to stronger EASM and higher spring rainfall. The ratio changed from <1 to >1 after 1950, reflecting that the summer quarter rainfall of the study area became dominant under stronger influence of the Northwestern Pacific High. Eastern China temperatures varied with the solar activity, showing higher temperatures under stronger solar irradiation, which produced stronger summer monsoons. During Maunder, Dalton and 1900 sunspot minima, more severe drought events occurred, indicating a weakening of the summer monsoon when solar activity decreased on decadal timescales. On an interannual timescale, dry conditions in the study area prevailed under El Niño conditions, which is also supported by the spectrum analysis. Hence, our record illustrates the linkage of Asian summer monsoon precipitation to solar irradiation and ENSO: wetter conditions in the study area under stronger summer monsoon during warm periods, and vice versa. During cold periods, the Walker Circulation will shift toward the central Pacific under El Niño conditions, resulting in a further weakening of Asian summer monsoons.
Im August 2015 legte eine Forschergruppe um Dianbing Liu in den Quaternary Science Reviews nach. Die Wissenschaftler dokumentierten einen deutlichen 200-Jahreszyklus, der dem solaren Suess-de Vries-Zyklus entspricht. Liu und Kollegen postulieren eine bedeutende solare Beeinflussung des Monsungeschehens in Zentral-China. Hier der Abstract:
Cyclic changes of Asian monsoon intensity during the early mid-Holocene from annually-laminated stalagmites, central China
Climate during the early Holocene was highly variable due to the complex interplay of external and internal forcing mechanisms. The relative importance for them on the Asian monsoon (AM) evolution yet remains to be resolved. Here we present two-to six-yr-resolution oxygen isotope (δ18O) records of five stalagmites, four of which are annually-laminated, from Qingtian Cave, central China, revealing detailed AM variability between 10.9 and 6.1 ka BP. Over the contemporaneous periods, the δ18O records agree well with each other at multi-decadal to centennial timescales. When pieced together with the previously published isotopic data from the same cave, the final δ18O record reveals detailed AM variability from the last deglaciation to the mid-Holocene, consistent with other cave records. The most striking feature of the δ18O record is the recurrence of centennial-scale oscillations, especially during the annually-counted period (8.8–6.1 ka BP). Cross-wavelet analyses between the δ18O record and solar proxies show strong coherence at 200-yr cycle, suggesting that solar output was actively involved as a primary contributor. The AM depression at 8.2 ka BP is indistinguishable in amplitude and pattern from a series of weak AM events after 8 ka BP. We speculate that these centennial-scale AM changes might be regulated by the positive feedbacks of oceanic/atmospheric interactions to the solar activity under the condition of the retreat of continental ice-sheets.
Im gleichen Monat erschien in den Quaternary Science Reviews auch die Arbeit einer Forschergruppe um Kan Zhao. Mithilfe von Isotopenuntersuchungen an Höhlen-Tropfsteinen aus Südwest-China rekonstruierten Zhao und Kollegen den Asiatischen Sommermonsun für die vergangenen 1200 Jahre. Auch hier erschien wieder der bereits beschriebene solare 200-Jahreszyklus des Suess-de Vries-Typs. IM Folgenden der Abstract:
A high-resolved record of the Asian Summer Monsoon from Dongge Cave, China for the past 1200 years
Two annually-laminated and 230Th-dated stalagmite oxygen isotope (δ18O) records from Dongge Cave, China, provided a high-resolution Asian Summer Monsoon (ASM) history for the past 1200 years. A close similarity between annual band thickness and stable isotope analyses (δ13C and δ18O) suggests the calcite δ18O is most likely a proxy associated with ASM precipitation. The two duplicated stalagmite δ18O records show that the ASM varies at a periodicity of ∼220 years, concordant with a dominant cycle of solar activity. A period of strong ASM activity occurred during the Spörer Minimum (1450–1550 A.D.), followed by a striking drop circa 1580 A.D., potentially consistent with the social unrest in the final decades of China’s Ming Dynasty (1368–1644 A.D.). Centennial-scale changes in ASM precipitation over the last millennium match well with changes in tropical Atlantic sea surface temperatures (SSTs) and South American summer monsoon precipitation. Our findings suggest that variations in low-latitude monsoon precipitation are probably driven by shifts in the mean position of the intertropical convergence zone (ITCZ), which is further mediated by solar activity and tropical SSTs.
Schließlich ist noch die Studie eines Wissenschaftlerteams um Jinguo Dong zu erwähnen, das im Oktober 2015 im Fachblatt Paleo3 erschien. Auch hier gehen die Autoren von einer maßgeblichen Monsunsteuerung durch die Sonne aus:
Reconciliation of hydroclimate sequences from the Chinese Loess Plateau and low-latitude East Asian Summer Monsoon regions over the past 14,500 years
We discuss replicated stalagmite δ18O records with interannual-to-multidecadal resolution from Lianhua Cave on the Chinese Loess Plateau to illustrate the precipitation history of the East Asian Summer Monsoon (EASM) region over the last 14.5 thousand years (ka BP, before 1950 CE, hereafter), and to re-evaluate the inconsistency in the proxy-inferred palaeoclimate time series in northern China. Agreement between the stalagmite δ18O from Lianhua and other caves from central-southern China indicates that regional climate changes after the Last Glacial were concurrent across mainland China, indicating that insolation was the primary factor controlling the evolution of the Asian Summer Monsoon (ASM). The stalagmite 18O enrichment of 2.5‰ in the Younger Dryas and 1.7‰ during the 8.2-ka BP event in Lianhua were larger than those in caves from central and southern China. The evidence suggests that different meridional responses of weak precipitation conditions in the ASM realm occurred during these two abrupt events, driven by high-latitude forcing in the Northern Hemisphere. The heterogeneous hydroclimate sequences in northern China inferred from different natural archives are most likely attributable to the complexity of the formations and/or some chronological uncertainty.
