Sonne macht Klima: Neues aus China

Schwankungen der Sonnenaktivität stellen einen bedeutenden Klimafaktor in China dar wie eine Vielzahl von Studien zeigt. Dies gilt auch für Tibet. Im November 2013 publizierte eine Forschergruppe um Yuxin He in den Quaternary Science Reviews eine Untersuchung zur Klimageschichte der letzten zweieinhalb Jahrtausende auf dem nördlichen Tibetplateau. He und Kollegen fanden starke natürliche Schwankungen, die gut mit der solaren Aktivitätsentwicklung korrelierten. Hier der Abstract:

Late Holocene coupled moisture and temperature changes on the northern Tibetan Plateau
The northern Tibetan Plateau involves complex interactions between the mid-latitude westerly circulation and the subtropical Asia monsoon circulation, acting as a bridge communicating high and low latitude climatic processes. Previous studies from the region suggest relatively wet conditions in cold periods during the late Holocene, for instance, the Little Ice Age (LIA). However, the inference of such temperature-moisture association is subject to the large uncertainty in lacustrine 14C chronology, due to the particularly large lake reservoir effect in the region. Here we take a different approach by reconstructing paired temperature and moisture records from the same sediment cores to assess the temperature-moisture association, independent of chronology uncertainty. We use alkenone indices UK′37 and %C37:4 to reconstruct high resolution temperature and moisture changes simultaneously from two lakes in the Qaidam Basin, northern Tibetan Plateau, over the last 2500 years. Characterized by marked climatic variability, our paired records confirm the warm-dry and cold-wet association in arid northwestern China during the late Holocene, opposite to the warm–wet and cold–dry association in subtropical Asian monsoonal regions. Our moisture records further suggest substantially drier conditions during the Medieval Warm Period (MWP) than the current warm period. Lastly, the temperature and moisture changes inferred from our records can be well correlated with solar irradiance changes, suggesting a possible link between solar forcing and natural climate variability during the late Holocene on the northern Tibetan Plateau.

Im April 2014 fügte ein Wissenschaftlerteam um Hai Xu eine weitere Studie zum Tibetplateau hinzu, die in den Quaternary Science Reviews erschien. Mithilfe von Isotopenuntersuchungen an Muschelkrebsschalen rekonstruierten die Forscher die Temperaturgeschichte und fanden erneut einen starken Bezug zu Sonnenaktivitätsschwankungen. Hier die Kurzfassung:

Decadal/multi-decadal temperature discrepancies along the eastern margin of the Tibetan Plateau
Knowledge of the synchronicity and discrepancy of temperature variations along the Eastern margin of the Tibetan Plateau (ETP) is critical in understanding the driving forcing of regional temperature variations. In this study, we established δ15N timeseries in organic matter and δ13C timeseries in ostracod shells from sediments of Lake Lugu and attributed their variations to decadal/multi-decadal temperature variations. We compared temperature variations along the ETP transect during the past four centuries based on our presently developed and previously developed temperature proxy indices, as well as temperature variations reconstructed by other researchers. We found that: (1) Over the north ETP area (N-ETP), the decadal/multi-decadal variations in temperature correlate well with each other. (2) Over the south ETP area (S-ETP), temperature variations correlate not so well with each other; while those at south to west portion of the Tibetan Plateau are rather local. (3) The decadal variations in temperature are generally synchronous with those in precipitation over the N-ETP area, and they are broadly anti-phase/out-of-phase with the corresponding ones over the S-ETP area. (4) The long term temperature and precipitation trends are coupling over the N-ETP but decoupling over the S-ETP. We speculate that because the N-ETP is located at the frontier of the Asian summer monsoon (ASM) region, temperature variations there are not as strongly influenced by the ASM; they are most likely dominated by changes in solar activities, and show general similarity to the average of the Northern Hemisphere. Over the S-ETP area, decadal temperature variations are obviously influenced by precipitation. Because the decadal/multi-decadal precipitation variations are anti-phase and/or out-of-phase between the N-ETP and S-ETP, the decadal/multi-decadal temperature variations between these two regions are also anti-phase and/or out-of-phase.

Und noch einmal Tibetplateau. Ein Forscherteam um Xiumei Li beschrieb im Juni 2015 in The Holocene eine Klimarekonstruktion für die vergangenen 2000 Jahre mit ausgeprägter solarer Suess-de Vries 200-Jahres-Zyklizität:

Centennial-scale climate variability during the past 2000 years on the central Tibetan Plateau
It is currently suggested that climate change on the northeastern Tibetan Plateau (TP) was influenced alternately by the monsoon and the Westerlies. However, the mechanisms driving Holocene climate change on the TP remain unclear, since the extent of the influence of individual atmospheric circulation systems has not yet been clearly defined because of the shortage of high-quality paleoclimatic records. This is especially true in the central TP, where only a few ice core and paleolimnological records are available. Here, we present a decadal-resolution temperature record from Dagze Co in the central TP for the past 2000 years, based on the unsaturation index of long-chain alkenones, using an updated temperature calibration, and a record of precipitation isotopes from compound-specific isotope ratios of leaf waxes. The centennial-scale variation of the temperature and precipitation isotope records captures well-known climatic events over the past 1000 years, for example, the ‘Little Ice Age’, which was cooler and drier than the ‘Medieval Warm Period’. However, the relationship between temperature and the precipitation isotope records differed during the interval at 2000–1000 cal. yr BP compared to the past 1000 years, probably because of changes in precipitation seasonality and the additional influence of the Westerlies on the central TP. In addition, the temperature records exhibit a prominent 210-year cyclicity, suggesting a possible influence of solar radiation on temperature variability.

Gehen wir nun in den Nordwesten Chinas. Auch hier prägt der solare Suess-de Vries-Zyklus das Klima, wie Tiwari und Rajesh im Mai 2014 in den Geophysical Research Letters dokumentierten. Die Autoren präsentieren eine Rekonstruktion der Niederschläge für die vergangenen 700 Jahre, wobei das Grundwasser im Takte der Sonne schrumpfte und expandierte:

Imprint of long-term solar signal in groundwater recharge fluctuation rates from Northwest China
Multiple spectral and statistical analyses of a 700 yearlong temporal record of groundwater recharge from the dry lands, Badain Jaran Desert (Inner Mongolia) of Northwest China reveal a stationary harmonic cycle at ~200 ± 20 year. Interestingly, the underlying periodicity in groundwater recharge fluctuations is similar to those of solar-induced climate cycle “Suess wiggles” and appears to be coherent with phases of the climate fluctuations and solar cycles. Matching periodicity of groundwater recharge rates and solar and climate cycles renders a strong impression that solar-induced climate signals may act as a critical amplifier for driving the underlying hydrographic cycle through the common coupling of long-term Sun-climate groundwater linkages.

Dasselbe Bild im Nordosten Chinas. Auch hier begegnen wir wieder dem Suess-de Vries Zyklus. Ein Forscherteam um Guoqiang Chu studierte dort jahreszeitlich geschichtete Seesedimente und fand neben dem 200-Jahreszyklus auch Zyklen des solaren Eddy- (1000 Jahre) und Gleissberg- (90 Jahre) Typs. Die Arbeit wurde im Oktober 2014 in den Quaternary Science Reviews publiziert:

Holocene cyclic climatic variations and the role of the Pacific Ocean as recorded in varved sediments from northeastern China
We present an n-alkane and compound-specific carbon isotope record of the past 9 ka from the annually laminated sedimentary sequence of Lake Xiaolongwan, northeastern China. The n-alkane distribution suggests that Lake Xiaolongwan has undergone a shift from an oligotrophic state with low algal production and little emergent/submerged macrophytes in the early Holocene, to a eutrophic state with high algal production and abundant emergent/submerged macrophytes since the middle Holocene. The pattern of variation observed in the biomarker proxies ACL (the n-alkane average chain length), Paq (aquatic macrophyte versus aquatic macrophyte and terrestrial plant ratio), and LPTP (lake productivity/terrigenous organic production) is throughout the record similar to that of the total organic carbon. The variation of compound-specific carbon isotopic values in the middle- and short-chain alkanes was mainly regulated by lake productivity and the accumulating organic pool through time. In this forested region, where the vegetation is dominated by C3 plants, the long-chain n-alkanes (C27–C31) are predominantly derived from leaf wax lipids. The compound-specific δ13C27–31 value is sensitive to effective precipitation, and therefore represents a useful indicator of regional monsoonal precipitation. Spectral analysis on the δ13C27–31 time series reveals significant periodicities of 87–89, 205–212, 1020–1050 and 1750–2041 years. On the centennial timescale, the quasi-periodicities around 88 and 210 years suggest a strong link between solar activity and monsoon rainfall. The millennial monsoon cycle in northeastern China is associated with sea surface temperature (SST) variations in two active centers of the summer monsoon, the western Pacific Subtropical High (WPSH) and the Okhotsk High. Increasing SST in the subtropical sea may cause a northwards shift of the WPSH, which extends the monsoon rain band (Meiyu) to northeastern China, and thus increasing rainfall in that region. Meanwhile, decreasing SST in the Okhotsk Sea may strengthen the Okhotsk high, bringing more moisture into northeastern China. We suggest that the Pacific Ocean is a main regulator for summer monsoon rainfall in northeastern China at present and at different time scales during the Holocene.

Bleiben wir noch kurz in Nordost-China. Einen bedeutenden Einfluss der Sonne auf das Klima fand hier auch eine Forschergruppe um Rong Chen, wiederum auf Basis von Seensedimenten. Die Arbeit erschien im März 2015 in The Holocene:

Mid- to late-Holocene East Asian summer monsoon variability recorded in lacustrine sediments from Jingpo Lake, Northeastern China
The Northeastern China involves complex interactions between the East Asian summer monsoon (EASM) circulation and the polar climate system, and plays a significant role as the bridge communicating low- and high-latitude climatic processes. High-resolution multi-proxy analysis of a robust accelerator mass spectrometry (AMS) 14C dated lacustrine sediment core recovered from Jingpo Lake in Northeastern China provides a detailed history of EASM variability and vegetation changes since ~5100 cal. yr BP. The period from ~5100 to 3600 cal. yr BP was characterized by the highest pollen percentages of Quercus, Ulmus, Juglans and Corylopsis; low Md (median grain size diameter); and high δ13Corg values, reflecting a relatively warm and humid period. The period between ~3600 and 2100 cal. yr BP is characterized by high Md and low δ13Corg values, and a rapid increase in pollen percentages of herbs, indicating cool and dry climatic conditions. From ~2100 to 150 cal. yr BP, a gradual increase in δ13Corg values and low Md values, and a rapid increase in Carpinus, Juglans and Corylopsis pollen percentages was observed, indicating climate change towards warmer and wetter conditions. After ~150 cal. yr BP, the highest values of total organic carbon mass accumulation rate (TOC-MAR), total nitrogen mass accumulation rate (TN-MAR) and magnetic susceptibility suggesting that the Jingpo Lake region has been severely affected by human activities. The EASM variability in Northeastern China during the mid- to late Holocene shows trends similar to EASM records in China. Furthermore, our findings indicate that the variability of the EASM during the mid- to late Holocene on the multi-decadal to centennial scale was forced by changes in both solar output and oceanic–atmospheric circulation interaction.

Schließlich sei noch ein Paper aus Süd-China erwähnt. Eine Forschergruppe um Wei Zhong dokumentierte im August 2014 im Journal of Paleolimnology eine solare Gleissberg-Zyklizität in der Klimaentwicklung, die zudem auch in anderen Punkten eine große Ähnlichkeit mit dem Verlauf der Sonnenaktivität aufweist:

Evidence of late Holocene climate variability in the western Nanling Mountains, South China
A 95-cm-thick peat sequence obtained from Daping Swamp in the western Nanling Mountains provides evidence for climate variability in the past ~3,000 year. Multi-proxy records (including organic carbon isotopes, humification degree, organic matter content, and dry bulk density) revealed three intensified Asian summer monsoon (ASM) intervals (i.e.~2900–2700, 2500–1700 and 1000–600 cal. yr BP) and three weakened ASM intervals (i.e.~2800–2500, 1700–1000 and 600–200 cal. yr BP). Our δ13C record shows a possible correlation with the sunspot number and residual atmospheric 14C records on multi-centennial scale, especially for the period between 2960 and 2200 cal. yr BP. A spectral analysis of δ13C record reveals three significant cycles (i.e., 396, 110 and 102 yr) and all these cycles could be related to solar activity, suggesting that solar output may have influenced the late Holocene climate variability in the study region.

Bei dieser Vielzahl von Hinweisen auf einen starken klimatischen Einfluss auf das Klimageschehen stellt sich automatisch die Frage, weshalb der IPCC noch immer davon ausgeht, die Klimawirkung der Sonne wäre nahezu vernachlässigbar. Wie lange ist diese fragwürdige Position angesichts der überwältigend klaren Literaturlage noch zu halten?