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5758
From: Akira, [DNS_Address]
Subject: 'exceptional' level of solar activity during the past 70 years
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Unusual activity of the Sun during recent decades compared to the previous 11,000 years S. K. Solanki1, I. G. Usoskin2, B. Kromer3, M. Schu ̈ssler1 & J. Beer4 1Max-Planck-Institut fu ̈r Sonnensystemforschung (formerly the Max- Planck- Institut fu ̈r Aeronomie), 37191 Katlenburg-Lindau, Germany 2Sodankyla ̈ Geophysical Observatory (Oulu unit), University of Oulu,90014 Oulu, Finland 3Heidelberger Akademie der Wissenschaften, Institut fu ̈r Umweltphysik, Neuenheimer Feld 229, 69120 Heidelberg, Germany 4Department of Surface Waters, EAWAG, 8600 Du ̈bendorf, Switzerland excerpt: "Direct observations of sunspot numbers are available for the past four centuries1,2, but longer time series are required, for example, for the identification of a possible solar influence on climate and for testing models of the solar dynamo. Here we report a reconstruction of the sunspot number covering the past 11,400 years, based on dendrochronologically dated radiocarbon con- centrations. We combine physics-based models for each of the processes connecting the radiocarbon concentration with sun- spot number. According to our reconstruction, the level of solar activity during the past 70 years is exceptional, and the previous period of equally high activity occurred more than 8,000 years ago. We find that during the past 11,400 years the Sun spent only of the order of 10% of the time at a similarly high level of magnetic activity and almost all of the earlier high-activity periods were shorter than the present episode. Although the rarity of the current episode of high average sunspot numbers may indicate that the Sun has contributed to the unusual climate change during the twentieth century, we point out that solar variability is unlikely to have been the dominant cause of the strong warming during the past three decades3. Sunspots—strong concentrations of magnetic flux at the solar surface— are the longest-studied direct tracers of solar activity. Regular telescopic observations are available after AD 1610. In addition to the roughly 11- year solar cycle, the number of sunspots, formalized in the group sunspot number1 (GSN), exhibits promi- nent fluctuations on longer timescales. Notable are an extended period in the seventeenth century called the Maunder minimum, during which practically no sunspots were present2, and the period of high solar activity since about AD 1940 with average sunspot numbers above 70. A physical approach to reconstruction of the sunspot number back in time is based on archival proxies, such as the concentration of the cosmogenic isotopes 14C in tree rings4–6 or 10Be in ice cores7,8. This approach has recently been strengthened by the development of physics- based models describing each link in the chain of processes connecting the concentration of cosmogenic isotopes with the sunspot number9–12. This advance allowed a reconstruction of the sunspot number since AD 850 based on 10Be records from Antarctica and Greenland13,14. The current period of high solar activity is unique within this interval, but the covered time span is too short to judge just how unusual the current state of solar activity is. Here we present a reconstruction of the sunspot number covering the Holocene epoch, the modern period of relatively warm climate that superseded the glacial period about 11,000 years ago. The reconstruction is based on D14C, the 14C activity in the atmosphere15 obtained from high-precision 14C analyses on decadal samples of mid-latitude tree- ring chronologies. The data set has been created in an international collaboration of dendrochronolo-gists and radiocarbon laboratories16. The absolutely and precisely dated original data set used for the sunspot number reconstruction is represented by the black line in Fig. 1. Starting at a level 15% higher than the reference level of AD 1950, the atmospheric 14C shows a long-term trend (indicated by the red line), which is mainly the result of changes in the intensity of the geomagnetic dipole field before and during the Holocene epoch. The fluctuations on shorter timescales predominantly result from variations of the 14C production rate due to heliomagnetic variability, which modulates the cosmic ray flux. The atmospheric 14C level may also be affected by changes in the partition of carbon between the major reservoirs, that is, deep ocean, ocean mixed layer, biosphere and atmosphere. Variations in ocean circulation17 could influence 14C via a variable uptake of CO2 into the ocean or by the exchange of 14C-depleted carbon from the deep ocean, but, owing to the rather small 14C gradients among the reservoirs, strong changes in these processes need to be invoked. For the Holocene, there is no evidence of considerable oceanic varia- bility, so we can assume that the short- and mid-term fluctuations of 14C predominantly reflect solar variability. This is supported by the strong similarity of the fluctuations of 10Be in polar ice cores compared to 14C, despite their completely different geochemical history18–20." |
5759
From: JTRIV, [DNS_Address]
Subject: Re: 'exceptional' level of solar activity during the past 70 years
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Hi Akira, So are you funded by Exxon? In the Koch brothers pocket? These are questions that are asked of people who bring up anything other than the so called consensus on global warming. Toe the line or your motivations will be questioned. Anyway Solanki's research is very interesting. I'm not sure if you saw this, but the most recent IPCC report had this chart of climate forcings. Note that at the bottom of the chart is solar which supposedly has little forcing and little baring on climate change.  Personally I don't think the Sun is the main driver behind the past 100 years of warming but I also have doubts it has as little impact as the IPCC suggests. Cheers Jim |
5761
From: Akira, [DNS_Address]
Subject: Re: 'exceptional' level of solar activity during the past 70 years
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Hey, I’m just a humble tooth seeker. ;)= damn, you ain’t easy to please….oh, and I don’t do charts. They give me hives or a migraine. Seriously, it’s a medical condition. |
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[5762]
5762
From: JTRIV, [DNS_Address]
Subject: Re: 'exceptional' level of solar activity during the past 70 years
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Hi Akira, > damn, you ain’t easy to please…. LOL... hey I'm just happy to see you researching these things. And the point of the graph is that even though the Sun was at high levels of activity during the 20th century climate scientists attribute virtually none of the planet's warming to the Sun. But then again they are quick to point out the calmer than the last few solar maximum as a reason for temperatures not increasing. Personally I don't think the Sun was a major contributor to 20th century warming but it also seems ironic that it is claimed a mild solar cycle can cause cooling but a series of active solar cycles can't cause warming. Cheers Jim |
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