After further research, new high-resolution ice core results (data points only a few hundred years apart) in 2000–2003 allowed us to distinguish which came first, the temperature rises or the CO2 rises. We found that temperature changes preceded CO2 changes by an average of 800 years. So temperature caused the CO2 levels, and not the other way around as previously assumed. The world should have started backpedaling away from blaming carbon emissions in 2003.
...As of August 2007, we've measured where the warming is occurring in a fair bit of detail, using satellites and balloons. The observed signature is nothing like the greenhouse signature. The distinct greenhouse signature is entirely missing:
There is no hotspot in the tropics at 10 km up, so now we know that greenhouse warming is not the (main) cause of global warming — so we know that carbon emissions are not the (main) cause of global warming.
...Doubling atmospheric CO2 from the pre-industrial level of 280ppm up to 560ppm (which is roughly were the IPCC says we will be in 2100) is calculated to raise the world's air temperature by 1.2C in the absence of feedbacks such as convection and clouds. This is what you would get if the air was in a flask in a laboratory. Everyone roughly agrees with that calculated result.
But the modelers assumed (bad assumption #2) that increased warming would cause more rainfall, which would cause more clouds high up in the atmosphere — and since high clouds have a net warming effect, this would cause more warming and thus more rainfall and so on. It is this positive feedback that causes the UN climate models to predict a temperature rise due to a rise in CO2 to 560ppm to be 2.5C - 4.7C (of which we have already experienced 0.7C).
But in September 2007, Spencer, who spent a few years observing the temperatures, clouds, and rainfall, reported that warming is actually associated with fewer high clouds. So the observed feedback is actually negative, so we won't even get the full 1.2C of greenhouse warming even if carbon levels double!
I assume that the global warming believers have a rational response. Perhaps the alleged evidence cited above is wrong. Perhaps it is right, but not as important as other evidence that should increase our confidence that CO2 is causing global warming.