It was more considerable than being off a few flips. I'll link to the article again. Note that for all four IPCC reports, the averages of their estimates all end up over the actual measurements.
I'm not trying to pull an Ad-Hominem but frankly I don't trust the analysis of a fancy sounding scientific organization I've never heard of, with members I never heard of, who are publishing AIDS denialists.
It's like you presented me with a 300lb fat man and told me he was an elite marathon runner and showed me all these charts, and anecdotes, and finishing times of him being an elite runner. Common sense and experience tells me there's something wrong with the claim, every other fat man who claimed to be a marathoner was actually slow, I know if I look long enough I'll find a picture of him hopping in a Taxi or walking a 10k and claiming it was 42, I simply don't trust the fat man as a source of fast running.
If the analysis in that article is correct it will be replicated in credible sources, if the analysis is flawed it will be confined to the denialist sphere.
The point of evidence is to distinguish between models. As we get more data, it'll help us distinguish between these possibilities.
The models are largely based on the same underlying science, where they vary is in different ways of applying the science. It's not like competing Copernican vs heliocentric models of the solar system, it's more like using algorithm X or Y to simulate phenomena Z, or what statistical model do we want to use to simulate phenomena W.
We've been waiting since the 70's and the evidence continues to get stronger. The longer we wait the more severe the consequences are and the harder it is to change direction. If you wait for absolutely incontrovertible evidence it will almost certainly be too late to stop serious warming. It's possible we've already passed the tipping point and are looking at an unavoidable increase of 2-3 degrees no matter what we do.
Except the evidence isn't growing stronger as a case for near future action. Instead we're seeing growing divergence between the predictions made and the actual climate.
Except it's still getting warmer, the rate is slightly slower but the abnormally high temperatures are getting higher, not lower. Scientists are seeing something that causes them to be more and more certain, I think there's a point at which you have to accept they're not all morons.