Background
The authors introduce their newest study by noting that "predicting our future influence on climate requires us to have confidence in the climate models used to make predictions, and in particular that the models' climate sensitivity and ocean heat storage characteristics are realistic," and they go on to say that that confidence may be gained "by assessing how well climate models reproduce current climatology and climate variability, and how their feedback parameters compare with estimates from observations."

What was done
In pursuit of these important goals, Crook and Forster first determined, as they describe it, "the surface temperature response contributions due to long-term radiative feedbacks, atmosphere-adjusted forcing, and heat storage and transport for a number of coupled ocean-atmosphere climate models," after which they compared "the linear trends of global mean, Arctic mean and tropical mean surface temperature responses of these models with observations over several time periods." They also investigated "why models do or do not reproduce the observed temperature response patterns," and they performed "optimal fingerprinting analyses on the components of surface temperature response to test their forcing, feedback and heat storage responses." The models involved in these tests were those of the World Climate Research Programme's Coupled Model Intercomparison Project phase 3 or CMIP3, while the real-world data employed were those of the HadCRUT3 database.

What was learned
The two University of Leeds (UK) researchers found that tropical 20th-century warming was too large and Arctic amplification too low in the Geophysical Fluid Dynamics Laboratory CM2.1 model, the Meteorological Research Institute CGCM232a model, and the MIROC3(hires) model "because of unrealistic forcing distributions," and they determined that "the Arctic amplification in both National Center for Atmospheric Research models is unrealistically high because of high feedback contributions in the Arctic compared to the tropics." In addition, they report that "few models reproduce the strong observed warming trend from 1918 to 1940," noting that "the simulated trend is too low, particularly in the tropics, even allowing for internal variability, suggesting there is too little positive forcing or too much negative forcing in the models at this time."

What it means
So how good are today's climate models? "Good enough for government work," as the saying goes, but apparently still lacking in many aspects of their ability to faithfully reproduce the climate of the past, which renders their ability to accurately portray the climate of the future rather questionable.