Tree rings show calendar of sun spot activity

Spottiest for 8,000 years

By Lucy Sherriff, 28th October 2004

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Sunspot activity is more intense now than at any point in the last 8,000 years, according to researchers at the Max Planck Institute in Germany. The solar scientists have constructed an 11,000 years record of solar activity based on tree ring data, and discovered that the last 70 years have been particularly spot-filled.

However, the results should not cause alarm, the scientists say, because 8,000 years ago there was a period of similar intensity, suggesting that the sun naturally cycles through more and less busy times. Sami Solanki, the scientist who led the research, says the sun will probably calm down again in the next few decades.

To track solar activity using trees, the researchers had to go looking for the presence of particular isotopes, like carbon14 and beryllium-10, that are formed in the atmosphere when cosmic rays – radiation from deep space – impact the planet. The sun deflects much of the cosmic radiation that would otherwise smash into the planet, but when solar activity is more intense, it deflects even more.

As trees grow, they absorb the carbon in the atmosphere and preserve a record of that particular year’s level of Carbon-14, among other things. So, by measuring the amount of the isotopes in each year of tree growth, or each tree ring, the researchers could identify periods of greater or lesser solar activity.

Sun spots and exactly how they affect the Earth’s climate is the subject of considerable scientific investigation. Our understanding of exactly what causes them is incomplete, to say the least. What is known is that they are caused by fluctuations in the sun’s magnetic field, which in turn is created by the ionised gas inside the sun acting like a dynamo.

Whether or not the spots affect our climate is a more contentious issue, and researchers hope this record could help settle the debate. ®