Recent Atmosphere-Ocean Coupled General Circulation Model (AOGCM) simulations of the twentieth century climate, which account for anthropogenic and natural forcings, make it possible to study the origin of long-term temperature correlations found in the observed records. We study ensemble experiments performed with the NCAR PCM for 10 different historical forced simulations, including no forcings, greenhouse gas, sulfate aerosol, ozone, solar, volcanic forcing and various combinations, such as natural, anthropogenic and all forcings. We compare the scaling exponents characterizing the longterm correlations of the observed and simulated model data for 16 representative land stations and 16 sites in the Atlantic Ocean for these forcings. We find that inclusion of volcanic forcing in the AOGCM considerably improves the PCM scaling behavior. The simulations containing volcanic forcing are able to reproduce quite well the observed scaling exponents for the land with exponents around 0.65 independent of the station distance from the ocean. For the Atlantic Ocean, simulations with the volcanic forcing slightly underestimate the observed persistence exhibiting an average exponent 0.74 as compared to 0.85 for the Kaplan reconstructed data.