A new paper in Nature Geoscience looks at the potential causes of the recent slowdown in global mean surface warming and identifies factors that, when combined, reconcile the long-term climate model projections with the observed short-term weather trends.
The El Niño/Southern Oscillation is responsible for a cooling trend of about –0.06°C, while aerosols and reduced solar irradiance cause a slightly bigger drop of –0.07°C. What this means, the abstract concludes, is that "there is little evidence for a systematic overestimation of the temperature response to increasing atmospheric CO2 concentrations in the CMIP5 ensemble."
In other words, once you account for observed natural variability, climate models are doing just fine.