evidence: GCMs are critical tools that enable us to improve the understanding and prediction of atmosphere, ocean, and climate behavior. Models allow us to determine the distinct influence of different climate features by providing a way of exploring climate sensitivities with experiments that cannot be performed on the actual earth. Changes can be made to one feature in a climate model, such as warming or cooling ocean surface temperatures, to discern the impact those changes have on the climate. The uses for climate modeling also include diagnosis and prognosis. An example of a diagnostic use is detection and attribution. Detection and attribution require first demonstrating that a detected change is statistically significant, and then attributing this change to unnatural causes such as the role of anthropogenic forcing in 20th century climate change. Prognostic climate modeling predicts future climate, such as global warming trends, using current or historic data (ocean structure, radiative forcing, etc) as a basis. Timescales for projection include seasonal/interannual variability, decadal prediction, and 21st century scenarios.