"This increase CANNOT be explained by volcanism- the isotopic ratio of carbon in the atmosphere show a similar sudden and escalating change- this change is consistent with what you would expect if this additional carbon was coming from fossil fuel burning. This change is the OPPOSITE of what you would expect from volcanism."

This is a strawman argument. No one is claiming that volcanism is increasing.

Now, if that graph is accurate, we can expect CO2 to soon reach 500 parts of million [.05 of percent]. When we reach .05 percent global CO2 and/or get 2/16th of inch per year of sea level rise, we might begin have something to worry about.
Meanwhile the sky isn't falling:
"Over the last 400,000 years the natural upper limit of atmospheric CO2 concentrations was about 300 ppm. Today, CO2 concentrations worldwide average about 370 ppm. Humans may be able to take credit for some of these additions, but not all of them. Earth's plant life will respond to soak up these additions with additional biologic activity, but this takes time. Meanwhile perhaps up to 9% of CO2 concentrations in the atmosphere today may be attributable to human-related activities like agriculture, industry, and transportation. Compared to former geologic periods, concentrations of CO2 in our atmosphere are still very small and may not have a statistically measurable effect on global temperatures. For example, during the Ordovician Period 460 million years ago CO2 concentrations were 4400 ppm while temperatures then were about the same as they are today."
http://www.geocraft.com/WVFossils/last_400k_yrs.html
Or
"Between 52 and 57 million years ago, the Earth was relatively warm. Tropical conditions actually extended all the way into the mid-latitudes (around northern Spain or the central United States for example), polar regions experienced temperate climates, and the difference in temperature between the equator and pole was much smaller than it is today. Indeed it was so warm that trees grew in both the Arctic and Antarctic, and alligators lived in Ellesmere Island at 78 degrees North.

But this warm period, called the Eocene, was followed by a long cooling trend. Between 52 and 36 million years ago, ice caps developed in East Antarctica, reaching down to sea level in some places. Close to Antarctica, the temperature of the water near the surface dropped to between 5 and 8 degrees Celsius. Between 36 and 20 million years ago the earth experienced the first of three major cooling steps."
http://www.pbs.org/wgbh/nova/ice/chill.html

It's known that human activity is responsible for putting CO2 into the atmosphere [millions of tons of it]. But human activity is not the only source of CO2 in the atmosphere and probably isn't a major source. Nor if total CO2 content were to double [780 ppm] that this would have a significant impact on global temperature:
"This contention was challenged by Idso (1989), who wrote -- in reference to the very data that were used to support the claim -- that "changes in atmospheric CO2 content never precede changes in air temperature, when going from glacial to interglacial conditions; and when going from interglacial to glacial conditions, the change in CO2 concentration actually lags the change in air temperature (Genthon et al., 1987)." Hence, he concluded that "changes in CO2 concentration cannot be claimed to be the cause of changes in air temperature, for the appropriate sequence of events (temperature change following CO2 change) is not only never present, it is actually violated in [at least] half of the record (Idso, 1988)." "
http://www.co2science.org/edit/v6_edit/v6n26edit.htm
CO2 is a greenhouse gas, but isn't a major greenhouse in our atmosphere- H20 is far more significant. And Methane is far more efficent as a green house gas.
Additionally CO2 is a needed gas to have in our atmosphere- elevated levels of CO2 does increase the productivity of farming and plant growth in general.
Now, if global temperature were to increase- lets say in next 50 years it increases by 1 degree, and let's say sea levels were to accelerate to say 3/16 of an inch per year. There is still no reason to see this as a paticularly bad situation. Like the stock market, I suspect the global temperatures will continue to rise, but it is possible that instead over the next 50 years the global temperature could drop or basically stay around same level.
I don't think that the "threat" from Global warming is pressing enough to warrant the govt interfering in the national economy. I do think it is worth the amount govt funds we are currently throwing at the issue in order to get more understanding. If the "threat" from global warming become most serious, I think a proper course would be allow new nuclear reactors to built. And if you want to hedge your bets, getting more nuclear reactors on line starting now would be a good way to manage this risk.
If people who are worried about CO2 can only propose expensive and foolish solutions [govt regulation and CO2 storage ideas] then how can you expect rational people to take this issue seriously? You want the US to build 20 more nuclear reactor as part of the solution to this apparent problem? That is being somewhat serious. [A 1000 new reactors would be *really* serious.

RL says:
"Now, the truly stupid will say, "well your ice core graph shows large fluctuations in the past few hundred thousand years, and we are still here- so cant be too bad a thing"

Those oscillations happened BEFORE we became a globe spanning civilization heavily dependent on agriculture! Does anyone really believe we can survive a large change without it killing billions and lowering the standard of living? Not to mention the loss of coastal cities?"

You have provided no evidence that GW is a threat to millions of people or a threat to farming. A 1 degree global temperature increase and 1 1/2 ft increase in sea levels over the next 100 year could improve farming condition in general and isn't a threat to coastal cities- not a significant threat as compared to the last 100 years [a non threat for the vast majority of cities].