Now I have to say it. I am not a climate scientist, but I do like fiddling about with graphs. So I combined two graphs, and present the result here, on the left. Being unskilled with Fireworks, the work is not very pretty, as I had to stretch it to make the dates align. (Yes, I know, manipulating the data, we're all at it). You should find that if you click the image, it will get bigger.
The top one is as it says, Surface and Satellite Temperatures, and the bottom one is of five measures of solar activity. The higher the line, the hotter the sun.
There is a fair match between the first wave, (1980), though there is a bit of a notch. The temperature starts to rise before the 1990 solar increase, though there is another temperature increase in the trough of the solar cycle also. The 1998 spike occurs in a trough. I suspect that this is what Friis-Christensen is trying to explain with his cosmic rays.
Whatever, the important point is that the solar activity does not explain the upward slope of the graph. For that, we need to factor in our greenhouse gases. See the graph here for demonstration of this point.
And this one, just for good measure:
The red line is the sun irradiance, and the blue line is the temperature. Not a very good match, especially in the last few years.
As I say, I am not a climate scientist, just a GP who is trying to explain what is going on to honest enquirers. To have any validity, we would need to look at things over a longer period.
Here is one I made earlier. There is a fair correlation between sun and temperature. The recent uptick on both graphs is striking, but, before you AGW skeptics get too excited, it stops at 1960, and the sun has been declining since then.
The solar cycle does have an effect, especially in the long term, but it is no good saying the sun is the root cause of the present warming. The facts are against this hypothesis.
Here's another illustration of why how the sun cannot explain current temperatures:
Click to make it bigger.
Conclusion: global climate is controlled by a number of factors: core heat, solar irradiance, clouds, greenhouse gases, volcanoes, ocean currents, and maybe unknown unknowns. Not aliens, although there will be some out there who may think so. There are other factors, like clouds, and the churning of ocean currents, and these all have an effect, and as time goes on and the computer models get better, we will get a better and better match between models and observations.
But the demand coming from a handful of skeptical climate scientists, that humanity must possess absolutely perfect knowledge before we act to curb our carbon is either disingenuous or obsessive. It is not reasonable, given the risks that are implicit in not taking action to curb our greenhouse gases.
I believe the underlying objection to AGW from the skeptic lobby is that to meet the challenge that global warming presents to mankind, we have to kiss goodbye to free market fundamentalism. That is the next debate we need to have - the economic debate.
As for the scientific debate, the refining of climate science will continue, the models will get better, and we should try out all the reasonable factors that the skeptics want come up with, but we should do this while in the process of decarbonising the world economy. And reforesting the deserts.