Climate Change: Caused by the Sun?

Global warming skeptics claim that changes in earth's temperature can be explained by the natural variability of the sun and that man-made greenhouse gases like carbon dioxide are not a significant factor.

I've been trying to investigate this claim. Here's what I found out so far:

Scientists who believe that recent global warming is caused by man-made CO2 concede that that the average global temperature is correlated with the sun's output until about 1975. But they argue that the correlation breaks down after that. That is certainly the case in this graph from the Laboratory for Atmospheric and Space Physics at the University of Colorado at Boulder, which compares global temperatures with the amount of energy flowing from the sun.

Source: http://lasp.colorado.edu/science/solar_influence/index.htm

As you can see, starting in the '70s the earth's temperature increases faster than the sun's output. The argument goes that some source other than the sun, namely CO2, must be responsible for the warming during these years.

This is a strawman argument, though, since the skeptics do not rely on solar irradiance to make their case. After all, even before 1975 the correlation is not that good. For example, temperature increased faster than solar irradiance in the early 1900s, even though cars and factories were pumping far less CO2 into the atmosphere than they do today.

Two prominent skeptics, Eigil Friis-Christensen and Henrik Svensmark (Advances in Space Research 20:4-5, pp. 913-921 (1997) http://www-ssc.igpp.ucla.edu/IASTP/43/) propose that sunspot activity, rather than solar irradiance, is what affects earth's temperature. The number of sunspots that appears on the sun's surface rises and falls in cycles of approximately eleven years. Some cycles are a little longer, some a little shorter. As shown in the second graph, the length of the sunspot cycle correlates with global temperature much better than solar irradiance.

However this data only goes until 1980, so it is unclear whether the correlation continues into the last three decades; I have not been able to find anything more recent. Note also that Friis-Christensen and Svensmark do not rule out the possibility that climate change is due to a mixture of solar activity and greenhouse gases.

So there's no smoking gun (or smoking chimney) yet. If anybody can point me to some more recent data on solar activity and climate, or some hybrid models that incorporate both sunspots and CO2, please comment.