John C. Fyfe, Nathan P. Gillett, Francis W. Zwiers. Overestimated global warming over the past 20 years. Nature Climate Change, 767–769 (2013) doi:10.1038/nclimate1972
Recent observed global warming is significantly less than that simulated by climate models. This difference might be explained by some combination of errors in external forcing, model response and internal climate variability.