|CCSM GIS NCAR|
|Frequently Asked Questions|
Currently the datasets can be downloaded in a GIS shapefile format.
Shapefiles are common GIS format that can be used in ESRI GIS software. Shapefiles can also be imported into other
commercial and open source GIS software packages.
Once you register an email will be sent to the address you supplied in the registration process. You must click on the link on that email in order to complete the registration process.
When you download a shapefile there is an associated projection file (.prj). The Climate Change Model is a Geographic Coordinate System on a perfect sphere with a radius of 6371.22 KM.
I'm working on using the CCSM-3 data to analyze different responses of the system due to different scenarios. I'm confused by the naming of the scenarios that appear in “Model Run Set” table, on the graphs and in the Help files. What is the difference between “Climate Change Commitment", “20th Century Freeze” and “20th Century Constant” scenarios?
The "Climate Change Commitment" and "20th Century Freeze" and “20th Century Constant” all represent the same scenario. Here terms "Freeze", "Commitment", and "Constant" are synonymous and here used interchangeably.
Climate models are not like weather forecast models. What you see in the model is correct from the modeling stand point. Years in the Control Run do not go together with calendar years, therefore the control run of the CCSM-3 does not project specific events at the exact time these events occur (like the 1997 El Nino). The CCSM control runs are designed to illustrate internal model variability, by having fixed external forcings. Projections may show warming of the sea surface but in a generic sense. It is more random and statistical representation of such events rather than actual. Therefore a specific event like an El Nino is in the model only in a statistical sense, not that one could look at sea surface temperatures for a specific time period and see a replication of an observed event. CCSM modelers may perform additional runs where they supply ocean observational data, which forces the system to incorporate interactions between ocean and atmosphere and pick out specific events like El Nino.
What is the meaning of the numbers within the data sets names, such as 2, 3, 5, 6, and 7? Are these indicating any simulation parameter, or set of parameters applied to run the simulation model? Should I focus on just one data set? If so, which one and what would be the rationale behind it?
The numbers 2, 3, 5, 6, 7 represent different ensemble members. Climate models are an imperfect representation of the earth’s climate system and climate modelers employ a technique called ensembling to capture the range of possible climate states. A climate model run ensemble consists of two or more climate model runs made with the exact same climate model, using the exact same boundary forcings, where the only difference between the runs is the initial conditions. An individual simulation within a climate model run ensemble is referred to as an ensemble member. The different initial conditions result in different simulations for each of the ensemble members due to the nonlinearity of the climate model system. Essentially, the earth’s climate can be considered to be a special ensemble that consists of only one member. Averaging over a multi-member ensemble of model climate runs gives a measure of the average model response to the forcings imposed on the model. Unless you are interested in a particular ensemble member where the initial conditions make a difference in your work, averaging of several ensemble members will give you best representation of a scenario. For more information on scenarios and ensembles see www.gisclimatechange.org/runSetsHelp.html
Elevation is an input in the model, however, it is not a DEM, the values are derived from the US Navy 10’ global topography dataset.
An ensemble average is preferable to use for general analysis rather than a specific ensemble member, however, whether or not to use the ensemble average depends on the analysis being done. Climate models are statistical representations of the Earth's climate, and are not intended to replicate specific weather events, nor should they be used that way.
More and more emphasis is being placed in the impacts community on not only using a single model for impacts but rather a range of models and arrive at a consensus answer. Would you consider making other GCMs also available in GIS format?
Comparing outputs from different GCMs does indeed gives more comprehensive view of climate change predictions and the uncertainties. Even though we are looking into providing results from other GCMs in the future, currently our data distribution agreement is with the CCSM only.