Back a good number of years I followed this issue really closely.  The question is do we actually have enough data, enough computing power, and enough knowledge of the meteorological phenomena to actually come up with a credible model to answer the question?  At that point, the answer was clearly not even close.  We didn't even have enough satellites built, yet alone launched, yet alone operating long enough to give us a reliable baseline.  I decided that there was no credible scientific evidence and would not be for quite a good while, so I lost interest in following the issue.  There may be now or soon, but I doubt it.

Let's consider a few fundamental concerns:

1)  Likely, the most significant concern is global cooling and another ice age.  According to most scientific research our planet has undergone numerous ice ages in the so called recent history.  Usually the ice ages last 100 000 + years and then each is followed by a brief 10 000 to 12 500 year thaw.  Guess what?  We're already 10 000 years into the thaw.  In the '70s the gloom and doomers were concerned with global cooling.  At that point the concern was particulate matter would block out significant amounts of sunlight and lead to massive cooling.  Since cooling was a natural trend, it seemed likely that if anything we would hasten another ice age.  Global warming wasn't even an issue.

2)  The quality of the meteorological data is poor.  Many of our most significant temperature readings are taken at airports.  These show massive planet wide warming.  However, this is probably largely spurious.  We know that when you add concrete, it creates a "heat island effect".  As runways have been built up at airports, as parking areas have been extended, as large malls and other businesses have developed nearby the temperature readings were sure to go up -- even if there had been a slight decline in global temperatures.  I could go on, but this demonstrates that much of the data is likely not worth much.

3)  The quality of the models are poor (or at least it was the last time I looked at them).  Think about clouds.  During the day they block the temperature, causing the area to stay cooler.  But at night they hold in the air, causing the are to cool down more slowly.  Thus, clouds have a moderating effect -- keeping temperatures from wild swings.  None of the models considered whether cloud formation might be dependent on some relevant factors.  For example, if the earth warmed, we might reasonably assume more water vapour would evaporate, thus blocking more sunlight and keeping peak temperatures down.  Or perhaps even the timing of the clouds might shift.  If more clouds formed during the day and dissipated at night, this sort of feedback mechanism might stabilise the temperatures substantially.  At the time I looked, not a single model even thought clouds were relevant to be considered.  Similarly, the treatment of the oceans which cover 70% of the planet's surface was sketchy at best.. 

4)  Ideally whatever model we develop should be a real scientific model -- one that we can test on Mars and Venus as well.  If we have a model and it correctly predicts the weather on Mars, Earth, and Venus for a few years, it likely is trustworthy enough to project it on Earth for a longer period.  (Unless bootstrapping errors are really significant.)  Many of the models that have been used are not believable in the short run, yet have been projected into the distant future.  Logically we should already have launched sophisticated weather satellites to study these planets.  Have we even designed them yet?  Are we really serious about this?  I don't think so.

5)  If we assume global warming is real and is catastrophic, does that mean the best approach to deal with it is to destroy our economy?  Absolutely not.  The Kyoto talks were a joke b/c they ignored all pollution coming from third world countries.  So the big industrial countries would simply move their industries to the third world -- not just shifting -- but actually causing more pollution (b/c stuff would need transported further to the markets) and destroying countless jobs.  (And don't tell me that these plants would be built using state of the art techniques.  In the third world?  Without mandatory laws and enforcement mechanisms?  Give me a break!)  What are the alternatives?  As I said earlier, we could increase particulate matter in the atmosphere to block sunlight or we could accomplish the same result by putting up thin mylar shields or increasing cloud formation during days. We could seed some iron poor parts of the ocean, to grow more algae, to absorb more CO2.  We could use advanced sequestration techniques (if we can prove they actually do more good than harm). 

I could go on, but I'm out of time.  I don't even have time to proof this, so sorry if it is sloppy.