The accuracy of the modeled present-day Greenland Ice Sheet (GrIS) is crucial for future projections of GrIS changes. In this study, we present a detailed evaluation of the modeled present-day GrIS sensitivity to different present-day climatology data sets and spin-up methods and further assess the influence of the modeled present-day GrIS on future sea level projections. Our study demonstrates that with present-day climatology data sets derived from the Regional Atmospheric Climate Model (RACMO2), the modeled ice volume, area, and elevation of the GrIS agree substantially better with observations compared to simulations with present-day climatology data sets from temperature parameterizations and ERA-interim reanalysis. With transient spin-up, the simulated rates of ice elevation changes for the 1993–2010 period are closer to observations than those with steady state spin-up. These results indicate that the RACMO2 forcing and transient spin-up may be preferable for use in the ice sheet model. Moreover, our results reveal that the present-day climatology data sets and spin-up methods affect future sea level projections. Using transient spin-up, the ice sheet model estimates a range of 26 mm in projected sea level rise by 2098 under the A1B emissions scenario, due to different present-day climatology data sets. Compared to the results with transient spin-up, the estimated sea level rise by 2098 is reduced by 5–21 mm with steady state spin-up. This discrepancy is attributed mainly to differences in ice thickness and ice velocity between the modeled present-day GrIS with transient and steady state spin-ups and the effect of paleoclimatic changes with transient spin-up.