The recent snow and cold weather in the Four Nations has, in some minds, shown that global warming is an evil plan, concocted by mad scientists, to enslave us. One of the reasons behind this belief is a confusion between weather and climate.

Weather is what happens on a day to day basis. It is notoriously variable. Even in the last ice age there would have been very hot summers from time to time. To distinguish between the two one needs to have regard to:

1. Long-term trends in the averages of such variables as temperature and precipitation. By long term I mean over hundreds of years. By average I mean that the data is averaged over a period of ten or more years.
2. Changes to the weather caused by events such as vulcanism.
3. Short-term cyclical factors of the order of up to 25 years such as El Nino or the sunspot cycle.
4. Longer term factors such as changes in the orbital characteristics of the earth or on earth factors such as the cessation or diminution of the North Atlantic Oscillation. The NAO is the current that flows from the Caribbean to Northern Europe, then up to Green land and back down the eastern seaboard of the USA to the Caribbean.

Taking these factors into account is not simple. Look for example at the sunspot cycle. Sunspots are dark areas that appear on the sun. The number of sunspots increases to a maximum and then declines to zero and then start to increase, so repeating the cycle. The key fact here is that the sun is hotter when there are sunspots, increasing as the number of sunspots increases, than when there are none. So in theory the earth should get, alternately, slightly warmer and then slightly colder. If the earth is warming then this will tend to amplify the warm maximum and minimise the effect of the cold minimum.

Detecting this change is difficult for a number of reasons. Firstly the cycles are not all the same length, neither is the cold minimum period always the same length nor  does the hot maximum always reach the same intensity. For example the current minimum is one of the longest in recent times and has only just started to turn.  To complicate matters every second cycle or in other words every 22 years, the suns poles change over. What was the north pole becomes the south and the old south pole becomes the north pole.

On earth as well things change. The earth might be in the grip of an El Nino event or there may have been a recent major volcanic eruption or the weather patterns may just be going through an extended ‘random’ change. As a result of all these factors it would be unreasonable to expect a clear cut effect.

If you go to http://solarscience.msfc.nasa.gov/images/Zurich_Color_Small.jpg you can see a chart of the sunspot cycle since 1750.

We are currently in the 24th minimum. The peak sunspot number varies between 68 and 250 or in other words by a factor of nearly four!. If you print out the graph and use a ruler you can measure a number of things. First whilst the average length of a cycle from one minimum to the next minimum is around 11.2 years it can vary from 8 years to nearly 15.5 -a range of nearly two times!. If you count the low (cold?) period as starting when the sunspot number decreases to 25 on the way down and to 25 again on the way up it appears that the length of this low time varies between 2.5 and 8 years – a range of over three times – with an average of 4 years! What is more it looks as though the current low time which has already been going 4 years could be 6 or 8 years in length. The peak sunspot number has exceeded 205 only three times in the last 260 years whilst it has been lower than 113 on five occasions. On the other 16 times it has been between the two.

Interesting though this may be what is the effect, if any, on the weather? Between around 1807 and 1827 the two low periods lasted five and eight years respectively whilst none of the peaks around  1805, 1816 and 1830 exceeded 113. This was an exceptionally cold period called the  Dalton minimum. Charles Dickens was a child in this period and it is thanks to the cold winters he experienced then that we owe his later writing about winters and Christmas. The previous minimum was over a 100 years long lasting the  whole of the 17th century and gave rise to the delightful paintings of winter by the Dutch master painters.

In more recent times it is not clear that the weather is linked to the cycles. The last cold period in Hertfordshire where we live was in the late 1970’s to the late 1980s during which time the sunspot cycle was either increasing to a maximum or decreasing from it. If you go back 22 years to around 1962 we get to a cold period once again. The winter of 1962 – 1963 was one of the coldest on record and it coincided with a minimum. Go back another 22 years to 1940. The winter of 1939 – 1940 was severe and in January there were frequent frosts and heavy falls of snow. Go back 22 years to 1918 and you get a year with millions dying from flu. Whilst the winter was only average it was preceded and followed by snowy winters. Go back another 22 years to 1896 and you read in the Stepney diary http://website.lineone.net/~fight/Stepney/weather.htm that the Thames froze over in 1895-6 although the other winters appear to have been relatively benign.

The winter of 1940 came just before a low period, that of 1917-8 coincided with a maximum as did that of 1895. So it is difficult, unequivocally  to link the winter weather fluctuations with the low period in the sunspot cycle, principally I think because there are so many other factors that can upset the relationship.

This has not of course stopped some scientists form abusing the data. A recent paper purported to show that sunspot cycles were the cause of current global warming. Hopefully the reader can see that the variability and confounding factors are so great that such a conclusion has to be nonsense, at best. It is, at best, poor science, done by poor scientists. At least they did not attempt to use the data to show the world was cooling. We still have that claim to look forward to!

If you wish to see images of the sun and sun spots go to http://sohowww.nascom.nasa.gov/sunspots/

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