"The idea was presented that an active sun (with lots of sunspots) deflects alot of cosmic rays. When the sun enters a less active period, it doesn't deflect as many. Cosmic rays, for example interstellar protons, collide with the upper atmosphere in large numbers, creating a particle shower of charged ions that catalyze the nucleation of water droplets and form clouds. It's been speculated that this phenomenon causes up to 2% variation in the amount of cloud formation globally. A google search will easily come up with at least one paper that state the effect has been determined to be statistically insignificant, and no correlation has been observed."

It seems to me that a 2% variation could be significant.

But btw, I don't accept it as the only factor. It *might* be one major factor. Just as I can't say that a significant increase in CO2 would not have any effect upon global temperature. There many factors which were not included in the show. But I do think it showed the obvious and that is that CO2 level is related to rising or lowering global temperatures but it isn't a causal factor [and we being brainwashed]. The show had science in it, but like almost all of these type of shows [including the best stuff you see in Nova] it's not science- it's polemic.

"That's not to say it isn't true, but this was the principle mechanism proposed in the video that explained the historical correlation between sunspot activity and global temperatures. IMO it's about as solid as the link between atmospheric CO2 and global temperatures. And either one of them is just a nuance of global climate fluctuations that are inherently chaotic. As such I doubt either one is really significant.

I think it's more likely that global climate is controlled directly by Solar Irradiance. Just look at seasonal changes in temperature and you'll have your proof. "Keep It Simple Stupid (KISS)" as the saying goes."

And similar to this the Milankovitch cycles.

"Now, explain to me why 10,000 years ago most of Canada was covered by a mile-thick ice sheet and I'll be impressed. So far neither anthropogenic CO2 nor sunspots explains an ice age. The former is too recent. The latter? Well, only if sunspots indicate massive change in solar output would I accept that theory."

Oh, that is easy to explain. For last 50 million year or so we have been in a cold period. The reason for this cooler period has to do the locations of the continents. Take Antarctic away from South pole [and leave open ocean] and global temperatures would rise significantly. Or change the arctic region by removing Greenland [the Antarctic has probably a bigger more certain effect, but no doubt Greenland's location and having Arctic partial enclosed by all the continents has a cooling effect. And/or it you instead completely seal off Arctic ocean that would have another major effect].
So for most of last 50 millions Earth has been on the brink of going into an ice age. The idea that we are on some kind of brink of getting dangerously warmer just isn't going to happen.

"Has anyone explored the effect on Solar Irradiance if the sun swallowed a large planet, or KBO ? What could possibly cause the Sun, a gigantic ball of nuclear fury 1.39 million km in diameter, and containing 98% of the mass of the solar system, to vary in it's output and cause an ice age on Earth? "

Obviously in say last billion years many large space rocks have hit the Sun. But a large planet hitting the Sun probably wouldn't cause a ice age- more likely get us much hotter- maybe simply kill most life on Earth. As explained above we already know a large part of why we have ice ages.
[of course dinosaur killer or smaller impactor hitting earth is probably going to affect climate- the question is how long term. And I have idly wondered what if ocean impactor threw water {10-20 cubic miles of it} into the high atmosphere- I don't know, just wondering:). Btw, obviously volcanic eruptions also would throw a sizable quantity water in higher atmosphere, too. ]

"We've got 50 years of fossil fuels left in my estimates. Probably more like 30 years. Which problem would YOU like to solve? From which angle should we tackle it? It's an open question."

Well, I think we should build more nuclear reactors- because I do think we shouldn't have the idea that huge increases in CO2 wouldn't have any effect- I don't mind if we live in a 500 ppm global CO2, but 1000 ppm global CO2 worries me a bit. So, I'm ok with cutting CO2- I just want to do it in a somewhat rational manner. And simplest and best way of reducing CO2 is by using more Nuclear reactors. Now if we didn't build one other nuclear reactor and we simply burned fossil fuels like mad, I'm not sure we would even get to 500 ppm- but I like to have wide margins- if for no other reason we simply can't predict the global political future even if we could somehow predict the other things.

Currently we get something like 20% of electrical power from Nuclear energy- France gets 80%. If we got 30-40% from nukes that would do a lot to reduce CO2- more than wind, solar AND major improvements of automobiles.

I think the main thing is the world isn't going end in 10 years- Al Gore's political career will be over in a couple years, but that isn't really anything to panic about.