Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP)

AC&C logo IGAC logo SPARC logo

The Atmospheric Chemistry and Climate Model Intercomparison Project is organized under the auspices of Atmospheric Chemistry and Climate (AC&C), a project of International Global Atmospheric Chemistry (IGAC) and Stratospheric Processes And their Role in Climate (SPARC) under the International Geosphere-Biosphere Project (IGBP) and World Climate Research Program (WCRP).

Background and Motivation

The simulations performed for the Climate Model Intercomparison Project (CMIP) phase 3 activity in support of the IPCC AR4 provided a tremendously useful resource for exploring issues of climate sensitivity, historical climate and climate projections. However, the radiative forcings imposed in both the simulations of the 20th century and the future projections varied from model to model due to varying assumptions about emissions, differences in the behavior of physical processes affecting short-lived species that were included, and differences in which processes and constituents were included at all. For example, only 8 of 23 CMIP3 models included black carbon while less than half included future tropospheric ozone changes. Furthermore, the CMIP3 archive does not include diagnostics of radiative forcing from aerosols, ozone, or greenhouse gases other than cabon dioxide. Hence it is not straightforward to understand how much of the variation between simulated climate in the models results from internal climate sensitivity and how much results from differences in the forcings.

The CMIP5 project similarly will have little information on aerosols or on gases other than carbon dioxide. As models progress to a more Earth System approach including more interactions with the biosphere, a larger number of climate-sensitive emissions are also being incorporated into models, which will lead to diversity in the projected emissions even though anthropogenic emissions should be quite uniform. Hence there is a need for characterization of the forcings imposed in the CMIP5 historical and future simulations, and for diagnostics to allow us to understand the causes of the differences in forcings from model to model. There is also a need to better constrain uncertainties due to natural emissions, projections of anthropogenic emissions, etc.

Finally, a wealth of new observations related to atmospheric chemistry can be used to evaluate and further our understanding of chemistry and climate. ACCMIP will take advantage of these measurements by performing extensive evaluations of the models, especially as regards their simulations of tropospheric ozone and aerosols, both of which have substantial climate forcing that varies widely in space and time. Sources such as the Tropospheric Emission Spectrometer (TES), Ozone Monitoring Instrument (OMI), and Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on the Aura satellite, the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), and the ground-based Aerosol Robotic Network (Aeronet) will be used, requiring the input of both the modeling and observational communities. The Atmospheric Chemistry and Climate Model Intercomparison Project attempts to meet these various needs through a set of coordinated simulations, diagnostics and evaluations.

ACCMIP participants include scientists at the following research centers or using these centers' models: CCC (Canada), CICERO (Norway), ECHAM (Germany), Hadley Centre/Met Office (UK), LLNL (USA), LSCE/IPSL (France), Meteo France (France), MIROC/CCSR/NIES (Japan), NASA GISS (USA), NASA GSFC (USA), NCAR (USA), NOAA GFDL (USA), PNNL (USA), and UKCA/NIWA (New Zealand). Researchers from Italy (JRC), United Kingdom (U. of Edinburgh, U. of York) and USA (EPA, NOAA, UC Irvine and University of Maryland) are also participating in analyses.

Data is being archived at the British Atmospheric Data Center, with a data access policy providing one year of access to participating groups only followed by general public access.

Further Information

+ Publications

+ Experiment and Output Specifications

+ Answers to Frequently Asked Questions

+ CMOR Tables and Notes

Internal Resources (password required)

+ Wiki with output notes and results


  • Apr 13-15, 2011 — 1st ACCMIP workshop, Toulouse
  • Sep 1, 2011 — Submission of past and future core simulation (most groups)
  • Jan 30 - Feb 1, 2012 — 2nd ACCMIP workshop, Pasadena, CA
  • July 31, 2012 — Papers must be submitted by this date for use in IPCC AR5 WGI
  • 2012 — Post-AR5 ACCMIP activities (ACCMIP_3, ACCMIP_4, etc)
  • Note that Tier 1 (secondary priority) results are to be submitted when available.


An initial meeting to better define the ACCMIP was held June 20th, 2009 at Jussieu in Paris, France. The first full ACCMIP workshop took place April 13-15, 2011, in Toulouse, France. The meeting was hosted by Meteo-France.

The second ACCMIP workshop took place Jan. 30 - Feb. 1, 2012 in Pasadena, CA, hosted by the Jet Propulsion Laboratory's Center for Climate Sciences (with additional support from IGAC and the US EPA).


For further information about ACCMIP, please contact one of the project co-chairs, Drew Shindell (formerly NASA GISS; now Duke Univ.) or Jean-François Lamarque (NCAR).