CMIP3 vs CMIP5

What is CMIP3 and CMIP5?

The Intergovernmental Panel on Climate Change (IPCC) gathers and reviews global climate models as part of the international climate change Assessment Reports. The ensemble of the models are called the Climate Model Intercomparison Project (CMIP).

Comparison of the CMIP5 and CMIP3 datasets

The CMIP5 and CMIP3 datasets each contain output from a large number of GCMs. CMIP5 contains more models than CMIP3 and the CMIP5 models are more advanced.

Both the CMIP5 and CMIP3 GCMs have been used to generate projections of future climate conditions across the globe. A direct comparison between the projections from the two datasets is not possible, as they use different scenarios describing the amount of greenhouse gas in the atmosphere in the future. CMIP5 uses Representative Concentration Pathways, whereas CMIP3 uses scenarios from the Intergovernmental Panel on Climate Change’s (IPCC) Special Report on Emissions Scenarios. For more information see  Emissions Scenarios).

The IPCC’s Fifth Assessment Report (AR5) is based primarily on results from the CMIP5 modelling using RCPs, but it also uses results from the CMIP3 modelling. The IPCC notes that, for both large-scale climate patterns and the magnitudes of climate change, there is overall consistency between the projections based on CMIP3 and CMIP5. Differences in global temperature projections are largely attributable to a change in scenarios.1

Further analysis by CSIRO that has focused on Australia and the Asia-Pacific region shows that the responses of temperature and precipitation in the region to an increase in global average temperature are similar between the CMIP3 and CMIP5 datasets.2 However, the CMIP3 simulations show a greater tendency towards decreases in precipitation in central and eastern Australia than do the CMIP5 GCMs.

Maps of Australia comparing CMIP3 Vs CMIP5 model results
Figure 1. Changes in temperature (in °C) for the annual, standard case, from CMIP3 (left) and CMIP5 (right). The middle panels are the P50 result. The P10 fields are along the top, and P90 along the bottom. (CSIRO/BOM Forthcoming)

A more detailed comparison of the CMIP5 and CMIP3 datasets is provided by the IPCC1 and, for Australia, by CSIRO.2

NARCliM and the Commonwealth’s National Climate Modelling

The NARCliM projections complement the national climate projections developed by CSIRO and the Bureau of Meteorology. Both sets of projections take large-scale information on the future climate from multiple Global Climate Model (GCM) simulations. However, there are differences between NARCliM and the national climate modelling.

The national climate projections use GCMs from the World Climate Research Programme’s Coupled Model Intercomparison Project phase 5 (CMIP5).3, 4 The NARCliM projections use data from the earlier CMIP3 project.56

The NARCliM projections are dynamically downscaled climate-change data using the WRF Regional Climate Model. The national climate modelling projections include some information obtained by using dynamical downscaling and statistical downscaling techniques.

What projections should I use?

Climate change projections for NSW are available from a number of sources. NARCliM and the national climate projections are the most recent. Both sets of projections provide robust information on possible changes to the climate of NSW and the ACT.

The NARCliM projections also represent the largest and most robust set of dynamically downscaled regional climate projections available for NSW and the ACT. The models used for NARCliM were chosen for their independence and skill and their ability to model important components of the NSW climate. However, NARCliM uses only a single emissions scenario.

The national climate projections cover a range of emissions scenarios and use the latest generation of global climate models from CMIP5. The national projections also provide some dynamically and statistically downscaled projections for certain parts of Australia.

Footnotes

  1. IPCC (2013) Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Stocker, TF, Qin D, Plattner GK, Tignor M, Allen  K, Boschung J, Nauels A, Xia Y, Bex V, and Midgley PM (eds.). Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. 1535 pp., doi:10.1017/CBO9781107415324.
  2. CSIRO and Bureau of Meteorology (Forthcoming). Climate Change in Australia, Projections for Australia’s NRM Regions, www.climatechangeinaustralia.gov.au
  3. http://cmip-pcmdi.llnl.gov/cmip5/
  4. Taylor KE, Stouffer RJ, and Meehl GA (2012) An overview of CMIP5 and the experiment design. Bull. Amer. Meteor. Soc., 93, 485–498. http://dx.doi.org/10.1175/BAMS-D-11-00094.1
  5. http://cmip-pcmdi.llnl.gov/cmip3_overview.html
  6. Meehl GA, Covey C, Taylor KE, Delworth T, Stouffer RJ, Latif M, McAvaney B, and Mitchell JFB (2007) The WCRP CMIP3 multimodel dataset: a new era in climate change research. Bull. Amer. Meteor. Soc., 88(9), 1383–1394. http://dx.doi.org/10.1175/BAMS-88-9-1383