Im Jahre 2001 veröffentlichte der US-amerikanische Klimaforscher Gerard Bond zusammen mit Kollegen im Fachblatt Science eine Arbeit, deren Bedeutung lange unterschätzt wurde. Die Wissenschaftler hatten Sedimentkerne aus dem Nordatlantik analysiert und herausgefunden, dass sich das Klima während der vergangenen 10.000 Jahre zyklisch im Millenniumstakt verändert hat. Hierzu gehört auch die Zykik der Römischen, Mittelalterlichen und Modernen Wärmephasen. Als Antrieb der Klimaschwankungen identifizierte die Bond-Gruppe solare Aktivitätsschwankungen. In unserem Buch „Die kalte Sonne“ sind wir ausführlich auf die Entdeckung eingegangen.
Natürlich passte Anhängern der menschengemachten Klimakatastrophe dieses Modell überhaupt nicht. Leider verstarb Gerard Bond viel zu früh 2005, so dass seine Forschungen ein jähes Ende nahmen. Lange wurde die Science-Studie ignoriert. Feinde der solar-bedingten Klimavariabilität versuchten zwischenzeitlich sogar, die Ergebnisse von Bond anzuzweifeln. Allerdings fanden andere Forscher eine Vielzahl von ähnlichen Fallbeispielen aus den unterschiedlichsten Teilen der Erde, bei denen die Sonne den Millenniums-Takt für die Klimarhythmik angab.
In der Februar-2015-Ausgabe des angesehenen Fachblatts Geology erschien nun eine Studie, die das Bond-Resultat von 2001 weitgehend bestätigt. Eine internationale Forschergruppe um Hui Jiang vom State Key Laboratory of Estuarine and Coastal Research in Shanghai rekonstruierte mithilfe Kieselalgen aus einem Tiefseebohrkern nördlich von Island die Temperaturentwicklung der vergangenen 9300 Jahre. Dabei fanden sie eine enge Beziehung zwischen den Klimaschwankungen und der Sonnenaktivität, insbesondere für die letzten 4000 Jahre. Maßgeblich beteiligt an der Studie war auch Raimund Muscheler von der schwedischen Lund Universität, der bereits zum Bond-Team der Publikation von 2001 zählte.
Im Folgenden die Kurzfassung der Arbeit:
Solar forcing of Holocene summer sea-surface temperatures in the northern North Atlantic
Mounting evidence from proxy records suggests that variations in solar activity have played a significant role in triggering past climate changes. However, the mechanisms for sun-climate links remain a topic of debate. Here we present a high-resolution summer sea-surface temperature (SST) record covering the past 9300 yr from a site located at the present-day boundary between polar and Atlantic surface-water masses. The record is age constrained via the identification of 15 independently dated tephra markers from terrestrial archives, circumventing marine reservoir age variability problems. Our results indicate a close link between solar activity and SSTs in the northern North Atlantic during the past 4000 yr; they suggest that the climate system in this area is more susceptible to the influence of solar variations during cool periods with less vigorous ocean circulation. Furthermore, the high-resolution SST record indicates that climate in the North Atlantic regions follows solar activity variations on multidecadal to centennial time scales.
Abbildung 1: Vergleich zwischen Temperaturschwankungen des untersuchten isländischen Kerns (blau) und der Sonnenaktivität (rot). Insbesondere für die letzten 4000 Jahre ist eine gute Korrelation erkennbar. Abbildung aus Jiang et al. 2015.
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Die Universität Aarhus gab zum Paper am 27. Februar 2015 die folgende Pressemitteilung heraus:
The sun has more impact on the climate in cool periods
The activity of the Sun is an important factor in the complex interaction that controls our climate. New research now shows that the impact of the Sun is not constant over time, but has greater significance when the Earth is cooler. There has been much discussion as to whether variations in the strength of the Sun have played a role in triggering climate change in the past, but more and more research results clearly indicate that solar activity – i.e. the amount of radiation coming from the Sun – has an impact on how the climate varies over time.
In a new study published in the scientific journal Geology, researchers from institutions including Aarhus University in Denmark show that, during the last 4,000 years, there appears to have been a close correlation between solar activity and the sea surface temperature in summer in the North Atlantic. This correlation is not seen in the preceding period. Since the end of the Last Ice Age about 12,000 years ago, the Earth has generally experienced a warm climate. However, the climate has not been stable during this period, when temperatures have varied for long periods. We have generally had a slightly cooler climate during the last 4,000 years, and the ocean currents in the North Atlantic have been weaker.
„We know that the Sun is very important for our climate, but the impact is not clear. Climate change appears to be either strengthened or weakened by solar activity. The extent of the Sun’s influence over time is thus not constant, but we can now conclude that the climate system is more receptive to the impact of the Sun during cold periods – at least in the North Atlantic region,“ says Professor Marit-Solveig Seidenkrantz, Aarhus University, who is one of the Danish researchers in the international team behind the study.
In their study, the researchers looked at the sea surface temperatures in summer in the northern part of the North Atlantic during the last 9,300 years. Direct measurements of the temperature are only found for the last 140 years, when they were taken from ships. However, by examining studies of marine algae – diatoms – found in sediments deposited on the North Atlantic sea bed, it is possible to use the species distribution of these organisms to reconstruct fluctuations in sea surface temperatures much further back in time. The detailed study makes it possible to draw comparisons with records of fluctuations of solar energy bursts in the same period, and the results show a clear correlation between climate change in the North Atlantic and variations in solar activity during the last 4,000 years, both on a large time scale over periods of hundreds of years and right down to fluctuations over periods of 10-20 years.
The new knowledge is a small but important piece of the overall picture as regards our understanding of how the entire climate system works, according to Professor Seidenkrantz. „Our climate is enormously complex. By gathering knowledge piece by piece about the way the individual elements work together and influence each other to either strengthen an effect or mitigate or compensate for an impact, we can gradually get an overall picture of the mechanisms. This is also important for understanding how human-induced climate change can affect and be affected in this interaction,“ she says.
Siehe auch Diskussion des Papers auf Climate Audit.
