This paper presents the theoretical characterization of the impact of nonlinear amplification on the spectral content of a carrier aggregated orthogonal frequency division multiplexing (CA-OFDM) system. Specifically, we derive a simplified mathematical expression of power spectral density (PSD) at the output of a nonlinearly amplified dual band CA-OFDM system. We show that nonlinear distortions caused due to nonlinear amplification severely affects the spectral content of dual band CA-OFDM signal, thus considerably increasing the adjacent channel power ratio (ACPR) at the output. Further, through the obtained results, we also demonstrate that the nonlinear amplification has far more adverse impact on a CA-OFDM system vis-a-vis non-aggregated OFDM system. A two-dimensional (2D) enhanced Hammerstein (EH) model is used to model the nonlinear behavior of the transmitter due to high power amplifier (HPA). A good agreement between the theoretical and simulation results demonstrates the accuracy of our analysis.