Spend any amount of time reading climate arguments on the Internet, and you'll undoubtedly hear some version of the following argument: the Earth hasn't warmed in 17 years, and none of the climate models predicted that. Although there are a lot of problems with that statement (including the fact that it has warmed a bit), it's probably safe to say that the warming hasn't been as intense as many scientists expected.
Of course, to a scientist, unmet expectations are an opportunity, so a variety of papers have looked into why this has happened. They've found that, while volcanic eruptions seem to have contributed to the relatively slow rise in temperatures, a major player has been the El Niño/Southern Oscillation (ENSO), which has been stuck in a cool, La Niña state for most of the last decade. And, since climate models aren't expected to accurately forecast each El Niño, there would be no reason to expect that they would match the actual atmospheric record.
At least not intentionally. But some researchers have found that, simply by chance, a few of the models do produce an accurate ENSO pattern. And when those models are examined in detail, it turns out they match the existing temperature record pretty well.