Technical notes (CMIP5)

Data and Processing:

The figures have been constructed using the Coupled Model Intercomparison Project Phase 5 (CMIP5) projections model output available at the PCMDI site (15 April 2014). This dataset comprises 29/29/29 scenario experiments for RCP2.6/4.5/8.5 from 29 climate models (Table 1) (CCCma). Only concentration-driven experiments are used (i.e., those in which concentrations rather than emissions of greenhouse gases are prescribed) and only one ensemble member from each model is selected, even if multiple realizations exist with different initial conditions and different realizations of natural variability. Hence each model is given equal weight. Maps and time series are provided for three RCPs.

Reference Period:

Projections are expressed as anomalies with respect to the reference period of 1986-2005 for both time series and spatial maps (i.e., differences between the future period and the reference period).

Equal Model Weighting:

The different CMIP5 models used for the projections in the plots are all considered to give equally likely projections in the sense of 'one model, one vote'. Models with variations in physical parameterization schemes are treated as distinct models.

Seasons:

The standard meteorological seasons, March to May, June to August, September to November, and December to February, are used.

Variables for graphics and tables:

Six variables are provided for CMIP5 graphics and tables: surface air temperature change, relative precipitation change, sea ice thickness change, sea ice concentration change, snow depth change, and near-surface wind speed change. The relative precipitation change is defined as the percentage change from the 1986-2005 reference period in each ensemble member.

For the time series, the variables are first averaged over the domain and then the changes from the reference period are computed.

Time Series:

The areal mean is computed on the common 1x1 degree grid using land points. As an indication of the model uncertainty and natural variability, the time series of each model and scenario over the common period 1900-2100 are shown on the top of the page as anomalies relative to 1986-2005. The multi-model ensemble means are also shown. Finally, for the period 2081-2100, the 20-year means are computed and the box-and-whisker plots show the 25th, 50th (median) and 75th percentiles sampled over the distribution of the 20-year means of the model time series, including both natural variability and model spread.

Spatial Maps:

Maps shown on CCDS show the difference between the periods, 2016-2035, 2046-2065 and 2081-2100, and the reference period, 1986-2005. The colour scale is kept constant for all maps.

Please note, as local projections of climate change are uncertain, a measure of the range of model projections is shown in addition to the median response of the model ensemble interpolated to a common 1x1 degree grid. It should again be emphasized that this range does not represent the full uncertainty in the projection. The distribution combines the effects of natural variability and model spread.

Please visit the Updates and Errata page for a list of modifications to CCDS.

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