In the year 1801, William Herschel, the famed musician, astronomer (he discovered Uranus) and mathematician made a curious discovery. Studying the price of wheat during the previous centuries he discovered a strange correlation between it and the number of sunspots on the face of the sun.
Digging through the records of wheat prices and the number of sunspots visible on the disk of the sun, Herschel discovered that during the years when there are few sunspots on the face of the sun, the price of wheat is high. Conversely, when there were lots of sunspots on the face of the sun, wheat prices are very low!
When we say there is a correlation between A and B, what we mean is that when A increases then B increases and when A decreases B follows and decreases at the same time. Similarly, two quantities, A and B, are anti-correlated if when A increases B decreases and vice-versa. Anti-correlation is often referred to as a negative correlation but the word negative has connotations among the illiterate of zero or no correlation at all. This is incorrect. Negative correlation is also a correlation but graphically the slope of the curve is descending from left to right.
Whenever two quantities are correlated or anti-correlated, there might be a physical connection that exists between them. For example, the average temperature at sea level decreases as one moves up in latitude towards the poles. There is a correlation between latitude on earth and average temperature. There is a physical reason for this: As one moves towards the poles, sunlight has to travel through a thicker layer of atmosphere which reduces its intensity on the ground. The correlation between latitude and temperature is thus a quantitative indication of an underlying physical cause.
While correlation is present among quantities that are physically related, not all correlations indicate the existence of a physical connection. In statistics, they say that correlation is not causation. Correlation is just a mathematical computation and it remains to be seen if one quantity indeed causes the other.
When two quantities are correlated (or anti-correlated) we do know that one of four possibilities must be true:
- A causes B,
- B causes A,
- A and B are both caused by another event C, and
- It is all a coincidence.
Going back to the discovery of William Herschel, is there a physical connection between sunspots and wheat prices? For almost two centuries solar physicists have sought to find the physical connection and found nothing. There does not seem to be any real physical connection between sunspots on the sun and the price wheat. How can an event on the surface of the sun affect how much people are paying for their wheat? While sunspots are indeed darker than the rest of the sun, they are only darker relative to the very bright sun. Indeed, the temperature of sunspots is still almost as hot as the rest of sun itself. No correlation has been found between the immediate temperature of the earth and the presence or non-presence of sunspots. Sunspots may be cooler but they apparently do not affect the instantaneous temperature on the earth.
Conversely, how can the price of wheat on earth affect the number of sunspots on the sun? Sunspots seem to follow an 11 year cycle and this 11 year cycle is certainly not caused by wheat prices on earth! Besides, the prices of wheat do not follow an 11 year cycle. Where did Herschel find his strange correlation, then?
He found it during grand minimums in the solar cycle. As I have said before, sunspots follow an 11 year cycle. During the minimum of such a cycle, the number of sunspots on the sun drop to zero or near zero but rise to over 100 during a typical maximum. However, twice during the last 500 years, the maximum sunspot number did not exceed the smoothed sunspot number of 50.
During the Maunder Minimum of the 1500s there were no sunspots on the face of the sun for several decades! It was also during the Maunder Minimum when the Little Ice Age gripped the earth and it was possible to walk from Manhattan to Staten Island because the water was frozen. During the Dalton Minimum of the late 19th century, it was almost the same with bitterly cold winters, mild summers and consequently high prices of agricultural goods.
The above brief about solar grand minimums is now relevant because at this very moment we are in a period of very few sunspots! We might be in a grand minimum again.
Solar cycle 24 is already more than a year late! It should have started to climb March of 2007 but as of today, April 2008, only two sunspots of solar cycle 24 have been spotted.
Some solar physicists are now fearing that the sun may be entering another grand minimum and consequently we should be expecting a return to the colder climate of the late 19th century (the Dalton Minimum) or even worse, a return to the little ice age.
Already, Russian scientists are making the bet that it will be bitterly colder during the next few decades and advice citizens to stock up on fur coats. Obviously, you haven't heard of that prediction which was made last year because the news agencies today are filled with dire predictions of global warming!
According to these Russians, anthropogenic global warming is bunk and the real crisis is the coming global cooling. They are saying that by 2012, there will be no doubt that the climate has shifted again (just as it always had in the past) and it will be colder again.
William Herschel's correlation has struck again and we are now in the regimen of an extended solar minimum (I won't call it grand minimum just yet) of very few sunspots and of a rising cost of agricultural goods.
China just experienced a bitter winter last December and January. I am not following agricultural news but if the rice harvest of Southern China was affected by the unusual cold of last winter then rice will definitely continue to be costlier as China scrambles to fill its deficit.
I had a chat with an officer of the Department of Agriculture office in our place and she told me that harvests this year are as good as last year's but that, surprisingly, some traders are buying rice from farmers at a higher than usual price! Hmmmmmn, I wonder if those buyers speak chinese?
