All models
used to project climate have some uncertainty associated with them, owing to
approximations that must be made in representing certain physical processes. To
understand the uncertainty in models, scientists compare them with other models
and evaluate how much the models differ in their projections. To determine
this, an ensemble of models is needed, allowing a range of simulations and
projections to be analyzed and compared. The World Climate Research Programme
has established the Coupled Model Intercomparison Project (CMIP) specifically
for this purpose. An agreed-upon suite of historical simulations and future
climate projections are performed using the same external forcing (changing
GHGs, land-use, etc.). The outputs from the models are archived in a common
format for analysis by the climate research community (Taylor et al., 2012).
Previous versions of CMIP have provided model results assessed in earlier IPCC
Assessment Reports. The most recent, fifth phase of this project, CMIP5,
provided climate model results that were assessed in the IPCC Fifth Assessment
Report (IPCC, 2013), and many of these results are available from the Canadian
Climate Data and Scenarios website. Future climate projections in CMIP5 used
the Representative Concentration Pathways emission scenarios (see Section 3.2)
(van Vuuren et al., 2011). A new version, CMIP6, is currently underway and will
serve as input to the IPCC Sixth Assessment.
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