Northumbria University: Solares Minimum der kommenden Jahrzehnte bringt klimatische Kühlung

Hans von Storch am 13. April 2019 in einem Spiegel Interview:

„Politisch legitim wäre die Haltung: Wir finden die Beweise unzureichend und warten daher noch mal ab. […] Ich sehe oft eher das Problem einer Überverkaufe der Ergebnisse der Klimaforschung: Manche Forscher haben die Robustheit unserer Ergebnisse übertrieben dargestellt und zu wenig auf Unsicherheiten der Erkenntnisse hingewiesen. Damit haben sie Vertrauen verspielt – und Zweifler erschaffen, Klimaskeptikerpropaganda regelrecht den Boden bereitet. Gestärkt wurden die Skeptiker auch dadurch, dass sie von Klimaforschern lautstark bekämpft wurden – so wurden die Skeptiker bekannt und trotz intellektuellen Siechtums immer wieder zum Leben erweckt.“

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Ende Juli 2019 erschien in Nature eine Arbeit von Toll et al. mit dem Titel „Weak average liquid-cloud-water response to anthropogenic aerosols“. Aerosol-Cloud-Interaktionen (ACI) sind i.d.R. großzügig in Klimamodellen eingebaut. Sie wirken kühlend. In den historischen Modellexperimenten führt das zu einer höheren Empfindlichkeit unseres Klimas gegenüber Treibhausgasen, die menschgemachten Aerosole „maskieren“ die Erwärmung. Nun ist ein guter Teil der angenommenen ACI allerdings abhanden gekommen in Beobachtungen, mit enormen Auswirkungen. Zitat:

The cancellations between increases and decreases in LWP [liquid water path] that we have observed in liquid clouds downwind of different aerosol sources under a wide range of meteorological conditions is in stark contrast to the unidirectional aerosol-induced increases in the LWP simulated by GCMs. Although in multiple GCMs an increase in the LWP enhances the Twomey effect by more than 100%, our analysis of pollution tracks show that decreases in the LWP in fact offset 23% of the Twomey effect….Now, our analysis of pollutiontracks shows with unprecedented confidence that the global average LWP response to anthropogenic aerosols is weak. We expect this constraint on the LWP response based on observations of pollution tracks to lead to improved aerosol-cloud parameterizations in GCMs and to translate into reduced uncertainty in aerosol forcing calculations and more reliable projections of future climate.

Zutreffendere Projektionen des zukünftigen Klimas durch Modelle wünschen sich die Autoren, und auch wir.

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Im Juni 2019 erschien im Nature-Ableger Scientific Reports ein spannendes Paper von Zharkova et al. Die Autoren analysieren die langperiodischen Sonnenzyklen und geben einen Ausblick über die zukünftige Entwicklung der Sonnenaktivität. Für die kommenden Jahrzehnte erwarten die Autoren einen Rückgang der Sonnenstrahlkraft auf das Niveau des Maunder-Minimums. Zudem sehen sie einen Einfluss der Sonne auf die klimatische Temperaturentwicklung der Erde. Im Abstract schreiben Zharkova und Kollegen von einer Erwärmung bis 2600 n. Chr.:

Oscillations of the baseline of solar magnetic field and solar irradiance on a millennial timescale

Recently discovered long-term oscillations of the solar background magnetic field associated with double dynamo waves generated in inner and outer layers of the Sun indicate that the solar activity is heading in the next three decades (2019–2055) to a Modern grand minimum similar to Maunder one. On the other hand, a reconstruction of solar total irradiance suggests that since the Maunder minimum there is an increase in the cycle-averaged total solar irradiance (TSI) by a value of about 1–1.5 Wm−2 closely correlated with an increase of the baseline (average) terrestrial temperature. In order to understand these two opposite trends, we calculated the double dynamo summary curve of magnetic field variations backward one hundred thousand years allowing us to confirm strong oscillations of solar activity in regular (11 year) and recently reported grand (350–400 year) solar cycles caused by actions of the double solar dynamo. In addition, oscillations of the baseline (zero-line) of magnetic field with a period of 1950 ± 95 years (a super-grand cycle) are discovered by applying a running averaging filter to suppress large-scale oscillations of 11 year cycles. Latest minimum of the baseline oscillations is found to coincide with the grand solar minimum (the Maunder minimum) occurred before the current super-grand cycle start. Since then the baseline magnitude became slowly increasing towards its maximum at 2600 to be followed by its decrease and minimum at ~3700. These oscillations of the baseline solar magnetic field are found associated with a long-term solar inertial motion about the barycenter of the solar system and closely linked to an increase of solar irradiance and terrestrial temperature in the past two centuries. This trend is anticipated to continue in the next six centuries that can lead to a further natural increase of the terrestrial temperature by more than 2.5 °C by 2600.

Der Zusammenhang zwischen Sonne und Temperatur wird im Haupttext näher erläutert:

Reconstruction of the cycle-averaged solar total irradiance back to 1610 suggests that since the end of the Maunder minimum there was the increase of the irradiance by a value of about 1–1.5 Wm−227,28, or about 3% of the total solar irradiance. This increase is correlated rather closely with the oscillations of the terrestrial temperature baseline26, which is found to steadily increasing since the Maunder minimum (e.g. recovering from the mini ice age). Although, it is not clear yet if this trend in the terrestrial temperature and solar irradiance is caused directly by the increased solar activity itself or by some other factors of the solar-terrestrial interaction in the whole solar system and human activities.

[….]

It can be noted that in many occasions the summary curve plotted backward for 3000 years in Fig. 1 reveals a remarkable resemblance to the sunspot and terrestrial activity reported for these 3000 years from the carbon isotope dating27. The summary curve shows accurately the recent grand minimum (Maunder Minimum) (1645–1715), the other grand minima: Wolf minimum (1300–1350), Oort minimum (1000–1050), Homer minimum (800–900 BC); also the Medieval Warm Period (900–1200), the Roman Warm Period (400–150 BC) and so on. These grand minima and grand maxima reveal the presence of a grand cycle of solar activity with a duration of about 350–400 years that is similar to the short term cycles detected in the Antarctic ice25,26. The 11/22 and 370–400 year cycles were also confirmed in other planets by the spectral analysis of solar and planetary oscillations29,30. The next Modern grand minimum of solar activity is upon us in 2020–20556.

Für die kommenden Jahrzehnte prognostizieren Zharkova und Kollegen eine abkühlende Wirkung der schwächelnden Sonne (dabei klammern sie anthropogene Effekte in der Betrachtung ausdrücklich aus):

[…] during the next two grand solar minima, which are expected to occur in 2020–2055 (Modern grand solar minimum lasting for 3 solar cycles) and in 2370–2415 (future grand solar minimum lasting for 4 cycles) (see Fig. 3 in Zharkova et al.6) a decrease of the terrestrial temperature is expected to be similar to those during the Maunder Minimum