Vindication of Edward Maunder minimum

No one took much notice of poor Edward Maunder

No one took much notice of poor Edward Maunder. He spent much of his adult life counting "sunspots" on the solar disc, and also browsing through records on the same topic left by his predecessors over the centuries.

Then in the early 1890s he was rewarded by what seemed to be a very interesting discovery. He published his findings in 1894, and again in 1922, on both occasions to a resounding burst of public and scientific apathy.

Throughout the records Maunder studied, the approximately 11-year cycle during which the number of sunspots waxes and wanes was clearly evident. But he noticed something else: between 1645 and 1715 hardly any spots had been noted by contemporary astronomers.

Those who bothered to read Maunder's accounts of his discovery assumed he had got it wrong, or that the solar watchers all those years ago had been a little lax. It was not until nearly 50 years after Maunder's death in 1928 that someone decided seriously to investigate this strange alleged anomaly.

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In the early 1970s an American astronomer, Jack Eddy, retraced the steps of Edward Maunder, and confirmed that what has now come to be called the Maunder Minimum really did exist.

Going even further, Eddy related the historical waxing and waning of sunspot activity to variations in the amount of the radioactive element Carbon-14 to be found in contemporary timber; in this way, using even older wood, he was able to extend the record of sunspot activity backwards to periods long before the era of the telescope.

Carbon-14 measurements confirmed the Maunder Minimum convincingly. And Eddy also identified two other anomalies: the so-called Spoerer Minimum from 1400 to 1510, and the Medieval Maximum, a period of unusually high sunspot activity from AD1100 until 1250.

Meteorologists in the intervening years have been quick to note that the two minima coincide nicely with the worst excesses of the "Little Ice Age" in the northern hemisphere, and that the Medieval Maximum occurred at a time when we know our climate to have been unusually benign.

The missing link, however, is any convincing mechanism by which sunspot activity might affect the climate of our planet. Some meteorologists have pointed out that cosmic radiation is modulated by the 11-year sunspot cycle, and suggest that this radiation may cause chemical changes in the upper atmosphere which may affect its transparency - and thus the radiation balance of the planet.

Others, however, while allowing there may indeed be some such mechanism, are still unconvinced that sunspots are a major factor in climatic change, or play any part in determining tomorrow's, or next century's, weather.