Nonetheless the thing persists.
In April 2008, an article appeared in The Australian alleging there had only been 3 sunspots since January and hence we were headed for an ice age. This article was rebutted by Melbourne academic David Karoly. On 15 May, a letter appeared in The Australian, claiming that Karoly had confused sunspot number (a calculated value) with number of sunspots. It's possible Karoly did, though he was correcting the previous article's manifestly wrong claim that there had only been 3 sunspots in total over a period when there had been many more.
This latest letter claims:
One visible sunspot is represented by a sunspot number of 11. Karoly writes that “the average number of sunspots a day last January was 3.4, followed by 2.1 in February and 9.3 in March’’. In fact, those numbers show months with many days of zero observed sunspots - a very quiet period on the Sun that has now extended longer than expected. Whether that affects the weather cannot be so easily disregarded as does Professor Karoly.
There does seem to be an interesting correlation between the length of sunspot cycles and climate change going back over centuries, compared with the 150 years that is all the CO2 warmers can work with.
There are several problems here.
For a start, it is incorrect to say that a sunspot equates to the number 11 in sunspot numbers. Let's see what the actual definition of sunspot numbers is:
An observer computes a daily sunspot number by multiplying the number of groups he sees by ten and then adding this product to his total count of individual spots... each daily international number is computed as a weighted average of measurements made from a network of cooperating observatories.
That is a nitpick of a nitpick so I will not dwell on it. The substance of the matter is his claim that sunspot cycles are a much better indicator of climate trends than modern models. Aside from the issue of more direct measures of solar output, the last sentence is bizarrely off target. Why should it be better to have centuries-long data of a phenomenon that did not exist centuries ago?
Anthropogenic carbon dioxide emissions began in earnest in the 18th century; by the close of the 19th century, they were less than 10% of current levels.
Saying that sunspot counts stood us in good stead for centuries so we should disregard other measures is like saying horse riding techniques stood us in good stead for centuries, so someone learning to drive a car should go to a riding instructor. In any case, the "centuries" claim is a tad inaccurate. The modern method of counting sunspots was invented in 1848.
Then there's the question of whether sunspot numbers actually correlate to the modern temperature trend. The IPCC has always stated in its reports that climate is a function of natural and anthropogenic influences, and even shows them separated out (here's a paper that does this nicely – see Figure 2(d) in particular, reproduced here). We would expect that solar output could be a major influence on climate before CO2 emissions became a major factor. But in recent years, this is not the case. In fact the trend in solar output is the opposite to that required to explain the warming trend in the late 20th to early 21st century.
If anyone asks nicely, I may even add in a few correlations.
But in the meantime, here is where you can find the data: