Hinweise auf Klimaeinfluss der Sonne verdichten sich weiter

In unserem Buch „Die kalte Sonne“ haben wir den enormen Einfluss von Sonnenaktivitätsschwankungen auf das Erdklima zeigen können. Die Forschung zum Thema läuft weiter auf Hochtouren. Im Folgenden wollen wir einige jüngere Arbeiten vorstellen.

Aus dem März 2016 stammt eine Arbeit von Yamakawa et al. in Quaternary International, in der die Autoren den solaren Klimaeinfluss über die Stratosphäre und die Meeresoberfläche beschreiben:

Relationships between solar activity and variations in SST and atmospheric circulation in the stratosphere and troposphere
Relationships between solar activity and variations in both sea surface temperature (SST) and atmospheric circulation at the time of the solar maximum are presented. The global distribution of correlation coefficients between annual relative sunspot numbers (SSN) and SST from July to December was examined over a 111-year period from 1901 to 2011. Areas with a significant positive correlation accounted for 11.7% of the global sea surface in December, mainly over three regions in the Pacific. The influence of solar activity on global atmospheric pressure variations and circulation in the maximum years was also analyzed from 1979 to 2011. The results indicated that higher geopotential height anomalies tended to appear in the stratosphere and troposphere in the northern hemisphere, centering on around the Hawaiian Islands from November to December, in the second year of the solar maximum. The SST distribution in the Pacific with strong north and south Pacific Highs produced a pattern that resembled teleconnection patterns such as the Pacific Decadal Oscillation (PDO) and the Central-Pacific (CP) El Niño, or El Niño Modoki (ENM). It is suggested that the solar activity had an influence on the troposphere via not only the stratosphere but also the sea surface.

Im Dezember 2015 war der Klimaeinfluss des solaren 11- Jahreszyklus Thema im AGU-Mitgliederblatt Eos:

[…] The Sun’s impact on the climate is a hot and tangled topic. Mounting evidence suggests that the 11-year solar cycle can affect climate and temperatures—the most famous example being Europe’s Little Ice Age, when the Sun went through several nearly sunspotless cycles from 1645 to 1715. […] Over the course of the 11-year cycle, the rotation of the Sun slowly twists its magnetic field into knots, creating dark sunspots. Although the overall brightness of the Sun varies by only 0.1%, the twisted bundles of magnetic energy can boost its ultraviolet (UV) radiation by 4%–8% at the solar cycle’s peak. These powerful UV rays trigger chemical reactions in the stratosphere that bind oxygen atoms and molecules to form ozone. Since ozone itself is a good absorber of UV radiation, it can heat the stratosphere near the equator, which affects the winds that circle the globe.

Ganzen Artikel in Eos lesen.

Eine Gruppe um Willie Soon publizierte im November 2015 in Earth Science Reviews zur Klimawirkung der Sonne im Rahmen der Erwärmung der letzten 150 Jahre:

Re-evaluating the role of solar variability on Northern Hemisphere temperature trends since the 19th century

Debate over what influence (if any) solar variability has had on surface air temperature trends since the 19th century has been controversial. In this paper, we consider two factors which may have contributed to this controversy:

1. Several different solar variability datasets exist. While each of these datasets is constructed on plausible grounds, they often imply contradictory estimates for the trends in solar activity since the 19th century.

Although attempts have been made to account for non-climatic biases in previous estimates of surface air temperature trends, recent research by two of the authors has shown that current estimates are likely still affected by non-climatic biases, particularly urbanization bias.

With these points in mind, we first review the debate over solar variability. We summarise the points of general agreement between most groups and the aspects which still remain controversial. We discuss possible future research which may help resolve the controversy of these aspects. Then, in order to account for the problem of urbanization bias, we compile a new estimate of Northern Hemisphere surface air temperature trends since 1881, using records from predominantly rural stations in the monthly Global Historical Climatology Network dataset. Like previous weather station-based estimates, our new estimate suggests that surface air temperatures warmed during the 1880s–1940s and 1980s–2000s. However, this new estimate suggests these two warming periods were separated by a pronounced cooling period during the 1950s–1970s and that the relative warmth of the mid-20th century warm period was comparable to the recent warm period.

We then compare our weather station-based temperature trend estimate to several other independent estimates. This new record is found to be consistent with estimates of Northern Hemisphere Sea Surface Temperature (SST) trends, as well as temperature proxy-based estimates derived from glacier length records and from tree ring widths. However, the multi-model means of the recent Coupled Model Intercomparison Project Phase 5 (CMIP5) climate model hindcasts were unable to adequately reproduce the new estimate — although the modelling of certain volcanic eruptions did seem to be reasonably well reproduced.

Finally, we compare our new composite to one of the solar variability datasets not considered by the CMIP5 climate models, i.e., Scafetta and Willson, 2014’s update to the Hoyt and Schatten, 1993 dataset. A strong correlation is found between these two datasets, implying that solar variability has been the dominant influence on Northern Hemisphere temperature trends since at least 1881. We discuss the significance of this apparent correlation, and its implications for previous studies which have instead suggested that increasing atmospheric carbon dioxide has been the dominant influence.

Von 2015 stammt auch ein Buch von Olavi Kärner mit dem Titel „Towards a New Climate Representation: Analysis of Forcing and Response Time Series„. Aus der Beschreibung:

This book provides a mutual analysis of temporal variability of total solar irradiance (TSI) at the top of the atmosphere (TOA) and various air temperature time series. The first part covers exploratory studies of the daily series in order to fit a statistical model for representing their long range temporal variability. The second part contains climatological interpretation of the fitted model. The results show essentially different temporal variability structure than that predicted by the theory of anthropogenic global warming.

Weiter mit einer Publikation aus dem Oktober 2015 in Advances in Space Research. Alexander Ruzmaikin und Joan Feynman dokumentieren darin den klimatischen Einfluss des solaren Gleissberg-Zyklus, der eine Periode von 90 Jahren besitzt:

The Earth’s climate at minima of Centennial Gleissberg Cycles
The recent extended, deep minimum of solar variability and the extended minima in the 19th and 20th centuries (1810–1830 and 1900–1920) are consistent with minima of the Centennial Gleissberg Cycle (CGC), a 90–100 year variation of the amplitude of the 11-year sunspot cycle observed on the Sun and at the Earth. The Earth’s climate response to these prolonged low solar radiation inputs involves heat transfer to the deep ocean causing a time lag longer than a decade. The spatial pattern of the climate response, which allows distinguishing the CGC forcing from other climate forcings, is dominated by the Pacific North American pattern (PNA). The CGC minima, sometimes coincidently in combination with volcanic forcing, are associated with severe weather extremes. Thus the 19th century CGC minimum, coexisted with volcanic eruptions, led to especially cold conditions in United States, Canada and Western Europe.

Im Mai 2016 veröffentlichten Al-Tameemi & Chukin im Journal of Atmospheric and Solar-Terrestrial Physics eine Analyse zum globalen Wasserzyklus. Interessanterweise fanden die Autoren eine deutliche Beeinflussung der globalen Verdunstung und des Wasserhaushaltes durch solare Aktivitätsschwankungen:

Global water cycle and solar activity variations
The water cycle is the most active and most important component in the circulation of global mass and energy in the Earth system. Furthermore, water cycle parameters such as evaporation, precipitation, and precipitable water vapour play a major role in global climate change. In this work, we attempt to determine the impact of solar activity on the global water cycle by analyzing the global monthly values of precipitable water vapour, precipitation, and the Solar Modulation Potential in 1983–2008. The first object of this study was to calculate global evaporation for the period 1983–2008. For this purpose, we determined the water cycle rate from satellite data, and precipitation/evaporation relationship from 10 years of Planet Simulator model data. The second object of our study was to investigate the relationship between the Solar Modulation Potential (solar activity index) and the evaporation for the period 1983–2008. The results showed that there is a relationship between the solar modulation potential and the evaporation values for the period of study. Therefore, we can assume that the solar activity has an impact on the global water cycle.

Im Februar 2016 erschien eine Arbeit von Kunihiko Kodera unter Beteiligung der Geomar-Forscherin Katja Matthes. Die Wissenschaftler beschreiben eine Erwärmung in mittleren Breiten durch den solaren Zyklus. Das Klimasignal wird dabei in der Stratosphäre durch die Sonne generiert und dann in die Troposphäre nach unten weiter gegeben:

How can we understand the solar cycle signal on the Earth’s surface?
To understand solar cycle signals on the Earth’s surface and identify the physical mechanisms responsible, surface temperature variations from observations as well as climate model data are analyzed to characterize their spatial structure. The solar signal in the annual mean surface temperature is characterized by (i) mid-latitude warming and (ii) no warming in the tropics. The mid-latitude warming during solar maxima in both hemispheres is associated with a downward penetration of zonal mean zonal wind anomalies from the upper stratosphere during late winter. During Northern Hemisphere winter this is manifested in a modulation of the polar-night jet whereas in the Southern Hemisphere the subtropical jet plays the major role. Warming signals are particularly apparent over the Eurasian continent and ocean frontal zones, including a previously reported lagged response over the North Atlantic. In the tropics, local warming occurs over the Indian and central Pacific oceans during high solar activity. However, this warming is counter balanced by cooling over the cold tongue sectors in the southeastern Pacific and the South Atlantic, and results in a very weak zonally averaged tropical mean signal. The cooling in the ocean basins is associated with stronger cross-equatorial winds resulting from a northward shift of the ascending branch of the Hadley circulation during solar maxima. To understand the complex processes involved in the solar signal transfer, results of an idealized middle atmosphere–ocean coupled model experiment on the impact of stratospheric zonal wind changes are compared with solar signals in observations. The model results suggest that both tropical and extra-tropical solar surface signals can result from circulation changes in the upper stratosphere through (i) a downward migration of wave–zonal mean flow interactions and (ii) changes in the stratospheric mean meridional circulation. These experiments support earlier evidence of an indirect solar influence from the stratosphere.

Weitere Beiträge zum Thema Sonne/Klima von Javier und Stefan Kämpe.

Angesichts der Vielzahl von Belegen zur starken Klimawirkung der Sonne wird es für die Sonnen-Gegner nun eng. Im Rahmen des Forschungsnetzwerks TOSCA haben sich einige Forscher zusammengschlossen, um die Sonne klimatisch abzuschalten. In einer Pressemitteilung vom 29. August 2016 behaupten sie, dass die Sonne nichts mit der globalen Erwärmung des 20. Jahrhunderts zu tun habe. Ironischerweise schreiben sie dann aber gleich im nächsten Satz, dass die Sonne sehrwohl im Jahrhundertmaßstab klimatische Wirkung entfaltet:

A changing Sun, a changing climate?
[…] By comparing recent measurements with results from new models, the network challenged the long-debated assumption that the Sun’s slight change in radiation could cause the Earth’s climate to change. They found mechanisms by which solar variation can alter climate variability regionally, but none that would trigger global warming. Looking at time scales longer than a century, the impact of solar variability on climate change is evident, but the effect of greenhouse gases has been proven much more considerable in the short run. However, there are still many questions behind the Sun-Earth connection, some of which TOSCA helped answer. By examining the different phenomena defining the solar impact on climate in general, the team showed several subtle phenomena could have a significant impact, often locally. For instance, UV radiation amounts to a mere 7% of solar energy, but its variation produces changes in the stratosphere near the Equator, all the way to the polar regions, which govern climate. This means that winters in Europe would become wetter and milder or, on the contrary, drier and cooler, depending on the Sun’s state. They also found that streams of electrons and protons known as the solar wind, affecting the Earth’s global electric field, lead to changes in aerosol formation, which ultimately impact rainfall. These effects, largely ignored so far, will now be incorporated into several climate models in order to build a more complete picture.

Einer der Leiter des TOSCA-Programms ist Benjamin Laken, der sich bereits in der Vergangenheit mit Kritik an Svensmark und seinem solaren Wolkenmodell profilierte. Seltsamerweise hatte Laken in früheren Arbeiten die Svensmark-Modelle noch unterstützt. Hin- und hergerissen zwischen solarem PRO und CONTRA geht es hier vielleicht aber auch um die wissenschaftspolitische Eignung für eine Institutsdauerstelle, wobei Sonnenkritik unabdingbar ist. In der Pressemitteilung heißt es:

Dr Benjamin Laken had a leading role in one of TOSCA’s training schools: “I demonstrated the use of Python for data analytics, and also guided a small team of students through an independent research project. This helped expose the students – many for the first time – to critical tools and methods relevant to their development into research. TOSCA enabled me to identify the most pressing knowledge gaps, which I could personally contribute to, and see how to effectively communicate my findings back to an interdisciplinary community. Thanks to the network, I was able to grow as a researcher at a critical time in my career.