The Coupled Model Intercomparison Project (CMIP) is a protocol for 1) systematically defining model simulations to be performed with coupled atmosphere–ocean general circulation models (AOGCMs) and 2) studying the generated output. This framework provides the scientific community with the ability to more easily and meaningfully intercompare model results, a process which serves to facilitate model improvement. However, the forcings imposed in simulations of the past or future varied from model to model due to varying assumptions about emissions, differences in the representation of physical and biogeochemical processes affecting short-lived species that were included (such as aerosols and tropospheric ozone and its precursors), and differences in which processes and constituents were included at all. The Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) aims to better evaluate the role of atmospheric chemistry (both gases and aerosols) in driving climate change. Effectively, ACCMIP targets the analyses of the driving forces of climate change in the simulations being performed in CMIP5.

The ACCMIP consists of a series of time-slice experiments targeting the long-term changes in atmospheric composition between 1850 and 2100, with the goal of documenting composition changes and the associated radiative forcing. In this overview paper, the ACCMIP activity, the various simulations performed (with a requested set of 14) and the associated model output are introduced.

This paper discusses and compares the 16 models, including the CAM model using the LLNL super-fast chemistry, that participated in the ACCMIP. Presented are the set of time-slice experiments defined to document the changes in atmospheric composition and in climate spanning 1850 to 2100. In addition, sensitivity experiments were defined to understand the main drivers behind tropospheric ozone and methane lifetime changes.

The 16 models described in this paper were used to perform the simulations needed for the analysis of various topics, namely 1) aerosols and total radiative forcing, 2) tropospheric ozone changes, 3) ozone radiative forcing and attribution, 4) comparison of ozone and associated forcing with TES, 5) black carbon deposition, and 6) OH and methane lifetime in the historical and future periods. Additional contributions and simulations are also planned for future analysis, focusing on air quality issues and additional understanding of simulated trends.