Along with the long-term global warming trend since the industrial revolution, observations of global averaged surface air temperature have also shown a decadal variability. Superimposing the climate variations with two time scales above can result in reduced or no warming in some decades such as 1999-2008 and increased warming in other decades such as 1980-1998. The main goal of this study was to explore the reasons that may cause the warming hiatus or accelerated warming periods by using a coupled global climate model (GCM) FGOALS-s2, developed at the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics (IAP), Beijing, China. The model reproduces not only the long-term warming trend, but also significant decadal variability. The global mean energy budget analysis indicates that the decadal variability of the global mean surface temperature is independent of the net top-of-atmosphere (TOA) radiation flux, implying that it may be associated with the re-distribution of heat in the climate system. Using composite analysis and regression analysis, the decadal characteristics of the global surface temperature and sea surface temperature (SST) were very similar in most regions: during the hiatus period, the SST decreased, and more heat flux penetrated into the subsurface or deep ocean; during the acceleration period, more heat was trapped in the upper ocean and the SST increased. Furthermore, on a decadal timescale, the climate variability of the Subtropical-Tropical meridional Cells (STC) played a crucial role in modulating the SST and the subsurface temperature in the Pacific Ocean. Remote responses of the anomaly wind stress and the net surface heat flux to the SST anomalies in the tropical Pacific can induce the decadal changes of sea temperature in the Indian Ocean and the Atlantic Ocean. In the processes associated with decadal variability, ocean circulations also play important roles, e.g., the Indonesian Throughflow (ITF) has a great impact on the changes of the subsurface sea temperature in the South Indian Ocean at decadal time scales, and the deep-ocean temperature in the Atlantic can be directly affected by the Atlantic Meridional Overturning Current (AMOC).