evidence: The results: 10 of the model projections closely matched observations. Moreover, after accounting for differences between modeled and actual changes in atmospheric carbon dioxide and other factors that drive climate, the number increased to 14. The authors found no evidence that the climate models evaluated either systematically overestimated or underestimated warming over the period of their projections. "The results of this study of past climate models bolster scientists’ confidence that both they as well as today’s more advanced climate models are skillfully projecting global warming," said study co-author Gavin Schmidt, director of NASA’s Goddard Institute of Space Studies in New York. "This research could help resolve public confusion around the performance of past climate modeling efforts." [...] To successfully match new observational data, climate model projections have to encapsulate the physics of the climate and also make accurate predictions about future carbon dioxide emission levels and other factors that affect climate, such as solar variability, volcanoes, other human-produced and natural emissions of greenhouse gases and aerosols. This study’s accounting for differences between the projected and actual emissions and other factors allowed a more focused evaluation of the models’ representation of Earth’s climate system.