Madam, – Dr Ian Elliott (January 19th), says “The recent behaviour of the sun indicates the onset of a prolonged period of solar inactivity. . .” leading to “many more cold winters”. And there is indeed evidence that reduced solar activity correlates with prolonged colder periods, not just winters.
We have indeed recently had one of the longest and most prolonged “solar minima” of recent years. But as the Maunder Minimum lasted for 70 years, through at least six of the Sun’s average 11-year cycles of activity, surely it is much too early to say that one long deep solar minimum (from which it is now recovering) indicates that such a prolonged period of low activity has commenced? The previous cycle was quite normal, so in fact we have only had reduced sunspot activity for a period of about three years.
We would need evidence of significantly reduced activity right up to the expected date of the next solar maximum, in about 2013-14, before we would have enough evidence to be concerned.
Solar activity is inherently variable, including the depth of minima, the height of maxima, and the length of the cycle which averages 11 years, but can vary between less than 10 and more than 12 years.
The excessively cold winters of 1947 and 1962-63, which were worse than the current one, were not accompanied by any reduction in solar activity, so in my view it is simply too early to say. – Yours, etc,