WCRP’s Coupled Model Intercomparison Project: a remarkable contribution to climate science
4 July 2017
by David Carlson1, Veronika Eyring2,3, Narelle van der Wel1, and Gaby Langendijk1
1 World Climate Research Programme, Geneva, Switzerland
2 Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
3 University of Bremen, Institute of Environmental Physics, Department of Climate Modelling, Bremen, Germany
As part of the Coupled Model Intercomparison Project (CMIP) organized under the auspices of the World Climate Research Programme’s (WCRP) Working Group on Coupled Modelling (WGCM) many hundreds of climate researchers, working with modeling centres around the world, will share, compare and analyze the latest outcomes of global climate models. These model products will fuel climate research for the next 5 to 10 years, while its careful analysis will form the basis for future climate assessments and negotiations.
CMIP started twenty years ago as a comparison of a handful of early global coupled climate models. In response to a growing need to systematically analyze coupled ocean and atmosphere model outputs from multiple climate modeling centres, it has subsequently grown into a large program to advance model development and scientific understanding of the Earth system. To meet these new goals, CMIP has developed well-defined climate model experiment protocols, formats, standards, and distribution mechanisms to ensure model output availability to a wide research community. The IPCC Fifth Assessment Report (IPCC, 2013) openly acknowledged a heavy reliance on CMIP Phase 5 (Taylor et al., 2012) and our analysis shows that approximately 45% of climate research papers published in 2016 in the Journal of Climate explicitly cite CMIP5. Dr David Carlson, Director of WCRP, emphasizes that “it’s really not possible to conceive or sustain the entire international climate research, assessment and negotiation processes without a community effort like CMIP at the heart of it.”
CMIP6 is now underway with the WCRP Grand Science Challenges (WCRP, 2016) as its scientific backdrop. A special issue in GMD describing the CMIP6 experiment design and organization has been published. These papers provide the information required to produce a standard set of climate model simulations that can be scientifically exploited to address the three broad scientific questions of CMIP6: (i) How does the Earth system respond to forcing?, (ii) What are the origins and consequences of systematic model biases?, and (iii) How can we assess future climate changes given internal climate variability, predictability and uncertainties in scenarios? An overview of the project is published by Eyring et al. (2016). That overview, combined with detailed descriptions of each of the 21 internationally-coordinated CMIP6-Endorsed Model Intercomparison Projects (MIPs) and the CMIP infrastructure and forcing datasets, specifies standard protocols, shared model diagnostics, and careful cross-comparison frameworks. These will allow researchers to investigate specific aspects of the climate system, from clouds to deep ocean circulation to an interactive carbon cycle. Each CMIP6-Endorsed MIP earned a commitment from at least 10 modeling centres to run all of the highest priority experiments and produce all the specified diagnostic outputs and information. The fact that CMIP6 elicits such a commitment from modeling centres indicates its enormous value to researchers and to society.
CMIP6 confronts a number of new challenges. More centers will run more versions of more models of increasing complexity. An ongoing demand to resolve more processes requires increasingly higher model resolutions. Archiving, documenting, subsetting, supporting, distributing, and analyzing the petabytes of CMIP6 model outputs will challenge the capacity and creativity of the largest data centres and fastest data networks. Fundamentally, CMIP6 will allow continuous and flexible model innovation schedules while remaining mindful of the IPCC process, will ensure that CMIP products address priorities identified by the climate research community, and will foster open and inclusive participation. Prof Veronika Eyring, researcher at the German Aerospace Center (DLR) and Chair of the CMIP Panel, outlines that “with CMIP6 we aim to achieve a balance between fundamental improvements of our modeling skills and rapid progress on urgent science questions – not an easy task for the modeling centres and researchers who analyze the data.”
The growing dependency on CMIP products by a broad research community and by national and international climate assessments means that basic CMIP activities, such as the creation of forcing datasets, the provision and archiving of CMIP products, and model development, require substantial efforts. CMIP continues to rely heavily on volunteer efforts by enthusiastic climate researchers. It represents one of society’s most robust and reliable sources for climate information – a source that deserves international acclaim and substantial ongoing support.
- Eyring, V., Bony, S., Meehl, G.A., Senior, C.A., Stevens, B., Stouffer, R.J. and Taylor, K.E., 2016. Overview of the Coupled Model Intercomparison Project Phase 6 (CMIP6) experimental design and organization. Geosci. Model Dev., 9(5): 1937-1958.
- 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. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp.
- Taylor, K.E., Stouffer, R.J. and Meehl, G.A., 2012. An Overview of Cmip5 and the Experiment Design. Bulletin of the American Meteorological Society, 93(4): 485-498.
- WCRP, 2016. WCRP Grand Challenges. Hp. Online. World Climate Research Programme.