Solar activity measured by isotope proxies revealed the end of 20th century was the highest activity in 1200 years
A 2010 paper (that I somehow missed) was recently highlighted by the blog The Hockey Schtick and I thought it worth mentioning here even if a bit past the publish date.
The work by Ilya G. Usoskin of the Sodankyla Geophysical Observatory at the University of Oulu, Finland was published in Living Reviews of Solar Physics. The paper examines records from two isotope proxies (Be10 and C14) and finds that solar activity at the end of the 20th century was at the highest levels of the past 1200 years. Excerpts follow along with a link to the full paper.
A History of Solar Activity over Millennia
Ilya G. Usoskin, Sodankyla Geophysical Observatory (Oulu unit), University of Oulu, Finland
Presented here is a review of present knowledge of the long-term behavior of solar activity on a multi-millennial timescale, as reconstructed using the indirect proxy method. The concept of solar activity is discussed along with an overview of the special indices used to quantify different aspects of variable solar activity, with special emphasis upon sunspot number.
Over long timescales, quantitative information about past solar activity can only be obtained using a method based upon indirect proxy, such as the cosmogenic isotopes 14C and 10Be in natural stratified archives (e.g., tree rings or ice cores). We give an historical overview of the development of the proxy-based method for past solar-activity reconstruction over millennia, as well as a description of the modern state. Special attention is paid to the verification and cross-calibration of reconstructions. It is argued that this method of cosmogenic isotopes makes a solid basis for studies of solar variability in the past on a long timescale (centuries to
millennia) during the Holocene.
A separate section is devoted to reconstructions of strong solar–energetic-particle (SEP) events in the past, that suggest that the present-day average SEP flux is broadly consistent with estimates on longer timescales, and that the occurrence of extra-strong events is unlikely. Finally, the main features of the long-term evolution of solar magnetic activity, including the statistics of grand minima and maxima occurrence, are summarized and their possible implications, especially for solar/stellar dynamo theory, are discussed.
4.4 Grand maxima of solar activity
4.4.1 The modern episode of active sun
We have been presently living in a period of very high sun activity with a level of activity that is unprecedentedly high for the last few centuries covered by direct solar observation. The sunspot number was growing rapidly between 1900 and 1940, with more than a doubling average group sunspot number, and has remained at that high level until recently (see Figure 1). Note that growth comes entirely from raising the cycle maximum amplitude, while sunspot activity always returns to a very low level around solar cycle minima. While the average group sunspot number for the period 1750 – 1900 was 35 ± 9 (39 ± 6, if the Dalton minimum in 1797 – 1828 is not counted), it stands high at the level of 75 ± 3 since 1950. Therefore the modern active sun episode, which started in the 1940s, can be regarded as the modern grand maximum of solar activity, as opposed to a grand minimum (Wilson, 1988b).
Is such high solar activity typical or is it something extraordinary? While it is broadly agreed that the present active sun episode is a special phenomenon, the question of how (a)typical such upward bumps are from “normal” activity is a topic of hot debate.
In this review the present knowledge of long-term solar activity on a multi-millennial timescale, as reconstructed using the indirect proxy method, is discussed.
Although the concept of solar activity is intuitively understandable as a deviation from the “quiet” sun concept, there is no clear definition for it, and different indices have been proposed to quantify different aspects of variable solar activity. One of the most common and practical indices is sunspot number, which forms the longest available series of direct scientific observations. While all other indices have a high correlation with sunspot numbers, dominated by the 11-year cycle, the relationship between them at other timescales (short and long-term trends) may vary to a great extent.
On longer timescales, quantitative information of past solar activity can only be obtained using the method based upon indirect proxy, i.e., quantitative parameters, which can be measured nowadays but represent the signatures, stored in natural archives, of the different effects of solar magnetic activity in the past. Such traceable signatures can be related to nuclear or chemical effects caused by cosmic rays in the Earth’s atmosphere, lunar rocks or meteorites. The most common proxy of solar activity is formed by data from the cosmogenic radionuclides, 10Be and 14C, produced by cosmic rays in the Earth’s atmosphere and stored in independently-dated stratified natural archives, such as tree rings or ice cores. Using a recently-developed physics-based model it is now possible to reconstruct the temporal behavior of solar activity in the past, over many millennia. The most robust results can be obtained for the Holocene epoch, which started more than 11,000 years ago, whose stable climate minimizes possible uncertainties in the reconstruction.
An indirect verification of long-term solar-activity reconstructions supports their veracity and confirms that variations of cosmogenic nuclides on the long-term scale (centuries to millennia) during the Holocene make a solid basis for studies of solar variability in the past. However, such reconstructions may still contain systematic uncertainties related to unknown changes in the geomagnetic field or climate of the past, especially in the early part of the Holocene.
Measurements of nitrates in polar ice allow the reconstruction of strong solar energetic particle (SEP) events in the past, over the five past centuries. Together with independent measurements of the concentration of different cosmogenic isotopes in lunar and meteoritic rocks, it leads to estimates of the SEP flux on different timescales. Directly space-borne-measured SEP flux for recent decades is broadly consistent with estimates on longer timescales – up to millions of years, and the occurrence of extra-strong events is unlikely.
In general, the following main features are observed in the long-term evolution of solar magnetic activity.
• Solar activity is dominated by the 11-year Schwabe cycle on an interannual timescale. Some additional longer characteristic times can be found, including the Gleissberg secular cycle, de Vries/Suess cycle, and a quasi-cycle of 2000 – 2400 years. However, all these longer cycles are intermittent and cannot be regarded as strict phase-locked periodicities.
• One of the main features of long-term solar activity is that it contains an essential chaotic/stochastic component, which leads to irregular variations and makes solar-activity predictions impossible for a scale exceeding one solar cycle.
• The sun spends about 70% of its time at moderate magnetic activity levels, about 15 – 20% of its time in a grand minimum and about 10 – 15% in a grand maximum. Modern solar activity corresponds to a grand maximum.
• Grand minima are a typical but rare phenomena in solar behavior. Their occurrence appears not periodically, but rather as the result of a chaotic process within clusters separated by 2000 – 2500 years. Grand minima tend to be of two distinct types: short (Maunder-like) and longer (Sp¨orer-like).
• The modern level of solar activity (after the 1940s) is very high, corresponding to a grand maximum. Grand maxima are also rare and irregularly occurring events, though the exact rate of their occurrence is still a subject of debates. These observational features of the long-term behavior of solar activity have important implications, especially for the development of theoretical solar-dynamo models and for solar-terrestrial studies.
Full paper here: A History of Solar Activity over Millennia (PDF)
However, according to the IPCC, none of this has nothing to do with 0.7C of global warming since the end of the Little Ice Age in 1850. And, even if you were to point it out to them for AR5, they have now clearly demonstrated they have no intention of paying any attention to any factual data that doesn’t fit the ‘CO2 and nothing else’ meme.