November 01, 2004
Sun Shines At 8000 Year Peak Of Brightness

The Sun's energy output is at an 8000 year peak and output may decrease sometime in the next few decades.

The activity of the Sun over the last 11,400 years, i.e., back to the end of the last ice age on Earth, has now for the first time been reconstructed quantitatively by an international group of researchers led by Sami K. Solanki from the Max Planck Institute for Solar System Research (Katlenburg-Lindau, Germany). The scientists have analyzed the radioactive isotopes in trees that lived thousands of years ago. As the scientists from Germany, Finland, and Switzerland report in the current issue of the science journal "Nature" from October 28, one needs to go back over 8,000 years in order to find a time when the Sun was, on average, as active as in the last 60 years. Based on a statistical study of earlier periods of increased solar activity, the researchers predict that the current level of high solar activity will probably continue only for a few more decades.

The research team had already in 2003 found evidence that the Sun is more active now than in the previous 1000 years. A new data set has allowed them to extend the length of the studied period of time to 11,400 years, so that the whole length of time since the last ice age could be covered. This study showed that the current episode of high solar activity since about the year 1940 is unique within the last 8000 years. This means that the Sun has produced more sunspots, but also more flares and eruptions, which eject huge gas clouds into space, than in the past. The origin and energy source of all these phenomena is the Sun's magnetic field.

Since increased sunspot activity is correlated with higher solar energy output it is possible that Earth climate temperatures in recent decades have been higher due to increased solar radiation hitting the Earth.

Because the brightness of the Sun varies slightly with solar activity, the new reconstruction indicates also that the Sun shines somewhat brighter today than in the 8,000 years before. Whether this effect could have provided a significant contribution to the global warming of the Earth during the last century is an open question. The researchers around Sami K. Solanki stress the fact that solar activity has remained on a roughly constant (high) level since about 1980 - apart from the variations due to the 11-year cycle - while the global temperature has experienced a strong further increase during that time. On the other hand, the rather similar trends of solar activity and terrestrial temperature during the last centuries (with the notable exception of the last 20 years) indicates that the relation between the Sun and climate remains a challenge for further research.

We are in an unusually long period of increased Solar activity. So an eventual decline seems highly likely. What we do not know is what will happen to Earth's climate when the Sun's output finally does decline. Depending on how far it declines cooling could become a bigger risk than warming. But we can't predict whether that will be the case. But human technology will advance so far in the next few decades that large scale climate engineering to cancel out either a warming or a cooling will become feasible. So either way I do not think we need to be deeply concerned in the short run.

This latest report builds on a previous research paper produced by Sami K. Solanki and colleagues several months ago which took a look at sunspot activity going back only 1000 years. See my previous post Sun Energy Output At Over 1,000 Year Peak for more information. Also see

Share |      Randall Parker, 2004 November 01 05:30 PM  Climate Trends

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