Climate History of Central Europe during the Little Ice Age

During the proposed project the relation between solar activity and climate should be investigated, based on the so-called Maunder and Spörer Minima, two long lasting periods (apr. 1645-1715, 1420- 1570) of strongly reduced sunspot formation, corresponding approximately to present solar minimum phases occurring every 11 years. As a first step, one must verify the source of the astronomic data once more, in terms of the apparent omissions of specifications regarding the corona in the recordings of eclipses before 1715. Moreover, one must clarify all contradictions, e.g. the apparently undisturbed continuity in the occurrence of naked-eye sunspots and aurorae, as they were noted by various authors in the period of the Maunder Minimum. Furthermore, the data material regarding telescopic observations from this period should be verified in terms of frequency, relevance and precision, so as to establish the reality of this exemplary minimum phase. The main point of interest of our research lies in the correlation of climatic information from the mentioned epochs and the reduced solar activity of that time. For this purpose, the geographic horizon which has been, until now, the main focus of the theory regarding the relation between reduced sunspot activity and cooler temperatures across the space of London and North-Western Europe is now extended into the South-East. First of all, the large amount of data, which is currently available for Switzerland and Germany must be compared to each other. The next step is the collection of comparable historical-descriptive material for the Eastern Alpine region of Austria and for Transylvania which was then politically connected to Austria. Afterwards, a comparative analysis of the new collected material is to be made and must be established in form of a data base including already existing material based on Glasers and Pfisters research, as well as partially reconstructed, partially observed sunspot activity. Moreover, from the cultural-historical point of view one should clarify existing questions in terms of the relevance of illustrations of severe winters in paintings of the Dutch masters, as well as others, who have depicted wintery landscapes during the time in question. A connection between the Little Ice Age and the Maunder Minimum has become so fixed in peoples minds that far-reaching conclusions have been made. US American researchers even claimed that the famous instruments of violin builder Stradivari, who had lived 1644-1737, just in the time of the Maunder Minimum, owed their unique sound to the slower growth of wood from that period, which was caused by reduced solar activity.

Time series of measured climate parameters are rarely longer than about a hundred years, and thus hardly go back to the time when the climate was still largely unaffected by human activities. Longer, high-quality time series would be extremely important, on the one hand, to better assess the magnitude of anthropogenic climate warming, and, on the other hand, to more accurately determine the frequency of extreme events, such as hot summers or cold winters. They can also help to determine the relative importance of natural climate changes. In this context, the so-called "Little Ice Age" (LIA) is of particular interest, which lasted from about 1300 to 1850 - especially since particularly cold phases during this period seem to coincide with periods of low solar activity, e.g. during the "Maunder Minimum" from about 1645 to 1715. In recent years, however, it has become more and more evident that the LIA was by no means homogeneous - neither in time nor in space. It is therefore important to study the climate evolution in different regions in detail - ideally based on measured data, or otherwise on historical records or proxy data, such as tree rings and the like. We have contributed to this endeavour by studying early measurement series in Paris and Graz, on the one hand, and by evaluating historical data in Transylvania, on the other hand, which have not been considered so far. It turns out that there were indeed very cold winters during the LIA - but also surprisingly hot summers in supposedly cold times. There is some evidence that even under natural conditions the frequency of hot summers was higher than we previously estimated - and that we are thus even underestimating the future frequency of hot summers in the course of climate change. Over the observed period, there is some correlation between climate change and reconstructed solar activity - but it is not particularly pronounced. Surprisingly, we have found some credible accounts of auroral observations in Transylvania during the period of the "Maunder Minimum", suggesting that solar activity during this time was not as low as often assumed.