1. …that the changes needed to reduce greenhouse gas emissions would damage the U.S. economy.
2. …that there is no cost to inaction.

Both of these assumptions are incorrect.

Studies show that the cost of inaction is far greater than the cost of taking action. Here are links to two posts that explain why in detail:

Green Technologies
We Can Do It, and at Moderate Cost

It's not hard to see that Wall Street under water will have a serious economic impact!

First, most skeptics understand that global climate is a "complicated system" as you say, and that's precisely why we aren't ready to accept "An Inconvenient Truth" as absolute truth. We recognize — in the spirit of scientific questioning — that there might be undiscovered explanations and we are therefor not willing to make the radical changes the true believers demand.

Second, be cautious about the country comparison charts. While it may be true that the U.S. uses more gasoline than Europe or Japan, what these comparisons FAIL to tell you is that the other countries use MASSIVE amounts of nuclear power. The U.S. has decided to limit use of nuclear power for a number of reasons. If we were to start building more plants, then you'd see the comparisons level off…. but you'd also see the environmentalists complain about use of nuclear fuel.

Additionally, the other factor is economic output. Sure we use more oil than France, but we also have a robust economy that allows for a high standard of living. France — where the people were protesting in the streets during the last presidential election because they didn't want to work more than a 30-hour-a-week schedule — has an economy that is LESS THAN THE STATE OF CALIFORNIA! It's true: California is the 5th largest economy in the world and regularly rivals France.

Bottom line: We could slow down our economy, work less, do less, and ultimately use less oil. But the United States just isn't that kind of a country. And for that reason country-to-country comparisons are quite misleading.

On CO2 amplification: I assume the orbital changes you referred to are the ~100ka and longer Milankovitch cycles. There are apparently many problems with this model ( http://en.wikipedia.org/wiki/Milankovich_cycles#Problems ) yet it seems to be uncritically accepted at RealClimate and by the IPCC. I don’t see how it can be valid to attribute most of the warming observed in glacial/interglacial transitions to CO2 when it seems so unlikely that the trigger has been properly understood.

On the Sun: There is evidence for the Sun’s activity increasing and cosmic ray flux decreasing (from proxies) to 1960. As you wrote in your third point, air pollution is believed to have caused cooling from 1940-1975. With pollution levels decreasing after 1975 it seems reasonable to expect to see temperatures return to 1940 levels and then continue to increase by an amount corresponding to the ‘masked’ solar activity increase from 1940 to 1960, despite there being no apparent trend in solar activity since 1960. Is this expectation realistic and if so is it accounted for in models?

There seems to be an assumption at RC, in the IPCC report and elsewhere that the lack of a recent trend in solar activity implies warming in this time period cannot be solar in origin (i.e. that the above process and any similar lagged solar influences are unrealistic) and much of the warming is thus (perhaps incorrectly) attributed to CO2. I know there will be some contribution to temperature changes in this period from CO2 and other sources – it is the magnitude of the contributions, that I question.

CO2 is not THE cause of global warming. It is A cause… one factor in the complicated system that is our atmosphere.

It just so happens that atmospheric CO2 is largely a byproduct of our own activities. That means we can change our behavior and reduce CO2 output. That one change, which we have control over unlike most of the other variables, may be enough to avoid disaster.

Why is that so hard to understand?

Off topic, but… The Economist had a great chart recently showing US gasoline consumption stacked up against every other industrialized nation in the world. We use more than all of them combined. This is our issue to take leadership on. If the US takes commits to action, the world will follow. Most of Europe is already on board.

Look at the recent furor over Chinese food safety. If China's, India's, et al, "customers" demand change they won't have a choice.

Re the amplification effect… The issue is that the orbital change – and resulting variation in solar energy output – is not enough to account for the large temperature fluctuations. The amount of warming this can produce is easily calculated – there's no dispute about this. Something else has to be going on. It turns out that this "something" is an amplification effect from the release of CO2 from the initial warming. The TV show itself talked about how warming leads to the release of CO2 from the oceans and other sources. That's not in dispute, either.

Re your second point… Sunspots are one of the main causes of the variability we see in solar irradiance (energy), which has increased slightly since 1750, but not nearly enough to explain today's rapid global warming. As shown above, irradiance has been flat over the past three decades. But let's say that sun spots are related to warming through their magnetic field strength. For the "Swindle" theory to be correct, you'd need to see a decrease in cosmic rays. But look at the graph – it's not there. The cosmic ray trend is flat, while global temperatures are spiking upward.

You can dig into all the details in the IPCC report. Chapter 6, Section 6.4 (pg. 444) covers glacial-interglacial cycles and CO2. Chapter 2, Section 2.7 (pg. 188) covers solar variability. RealClimate also has good posts here and here.

I have a problem with the idea that the ice core data shows an amplification or positive feedback effect due to CO2.
I understand that as a GHG CO2 will contribute to temperatures at least a little in this way but I know of no reason why the vast majority of the warming and CO2 release cannot be caused by the same thing that triggered it.
Also, what is the explanation for the periods in which temperature decreases while CO2 is still increasing?

I also have a problem with what you've said about sunspots.
My understanding is that sunspots correspond to the solar magnetic field strength rather than solar energy output and it is the magnetic field that affects the solar wind and cosmic rays. The sun's level of magnetic activity has been increasing over the past 100 years – this results in fewer clouds and an increasingly greater amount of the (approximately constant) solar energy output reaching Earth's surface.

The cosmic ray count data shows a slight decrease in counts over time. This is what is expected for a solar magnetic contribution to global warming.