NCAR Science & Research Data for IPCC AR4 Data Guide

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Spatial Extent:	Global
Spatial Resolution:	1.40625 degree gridded
Temporal Characteristics:
Date Classes Represented:	Time-series
Time Steps Available:	Monthly, daily (coming soon)
Dates represented:	1870 to 2100

Any use of the National Center for Atmospheric Research (NCAR)'s Community Climate System Model, version 3 (CCSM3) data should acknowledge the contribution of the CCSM project and CCSM sponsor agencies with the following citation:

"'This research uses data provided by the Community Climate System Model project supported by the Directorate for Geosciences of the National Science Foundation and the Office of Biological and Environmental Research of the U.S. Department of Energy." In addition, the words 'Community Climate System Model' and 'CCSM' should be included as metadata for webpages referencing work using CCSM data or as keywords provided to journal or book publishers of your manuscripts. Users of CCSM data accept the responsibility of emailing citations of publications of research using CCSM data to: ccsm@ucar.edu. Any redistribution of CCSM data must include this data acknowledgement statement.

Please also acknowledge EOS-WEBSTER as the data distributor when using these data in subsequent models or publications.

The NCAR Science and Research Data for IPCC AR4 data collection can be ordered from the EOS-WEBSTER Search and Retrieve Tool.

Additional climate change data, links, and resources are available from the Climate Change Resources page.

Summary:

The United Nations and World Meteorological Organization established the Intergovernmental Panel on Climate Change in 1988 to assess the scientific, technical and socio-economic information necessary to understand climate change, its potential impacts and options for adaptation and mitigation. The IPCC provides periodic assessments of the scientific understanding of climate change and its consequences, drawing on the expertise of scientists worldwide. The IPCC is widely recognized as the world's foremost authority on climate change.

The IPCC released three assessment reports in 1990, 1995, and 2001. A fourth assessment report (AR4) is scheduled for release in 2007. The IPCC does not carry out research nor does it monitor climate-related data or other relevant parameters. It bases its assessment mainly on peer reviewed and published scientific literature. Climatological datasets that are key inputs into the 2007 assessment report are now available through EOS-WEBSTER.

EOS-WEBSTER has developed the NCAR Science and Research Data for IPCC AR4 collection from the National Center for Atmospheric Research's Community Climate System Model, version 3 (CCSM3). The NCAR/IPCC AR4 collection is intended to provide the scientific community and other stakeholders easy access to these important data sets.

The collection contains model projections of climate from four scenarios used in AR4. Scenarios are based on storylines regarding levels of atmospheric CO₂, population growth, land-use changes, new technologies, and energy resources. Scenarios used in AR4 are described below.

The model was run for each scenario as an ensemble or collection of simulations. Ensemble members represent different initial conditions. This collection includes each ensemble member as well as the ensemble means that can be ordered individually. For more information on the NCAR CCSM3 ensembles, please contact Gary Strand.

Please Note:

EOS-WEBSTER has two collections of IPCC data using the NCAR CCSM3 model. A smaller set of variables have been aggregated into annual and decadal values for the ensemble means and are contained in the Climate Changes in the 21st Century data collection.

The Climate Changes in the 21st Century data collection is particularly well suited for educational use and is intended for middle school through college students as well as members of the general public. This collection, NCAR Science and Research Data for IPCC AR4, is best suited for scientific and research purposes.

Community Climate System Model, version 3 (CCSM3)

The National Center for Atmospheric Research (NCAR) in Boulder , Colo. , has developed a powerful supercomputer-based system to model Earth's climate and to project global temperature rise in coming decades. The model, called CCSM3, is yielding new insight into the complexities of the Earth system and the likely responses of our planet to natural and man-made influences.

CCSM3 is one of the world's leading general-circulation climate models, which are extraordinarily sophisticated computer tools that incorporate phenomena ranging from the effect that volcanic eruptions have on temperature patterns to the impact of shifting sea ice on sunlight absorbed by the oceans. Climate models work by solving mathematical formulas, which represent the chemical and physical processes that drive Earth's climate, for thousands of points in the atmosphere, oceans, sea ice, and land surface. CCSM3 is so complex that it requires about 3 trillion computer calculations to simulate a single day of global climate.

In addition to simulating temperatures over the next century, scientists will use the model to study climate patterns of the past, such as the peak of the last ice age 21,000 years ago. They will also use it to probe chemical processes and the cycling of carbon between the atmosphere, ocean, and land, as well as the localized impacts of sulfates and other pollutants on climate.

Datasets available from the NCAR Science and Research Data for IPCC AR4:

Dataset	Description	IPCC Name	Dates
Climate of the 20th Century	Atmospheric CO₂ concentrations and other input data are based on historical records or estimates beginning around the time of the Industrial Revolution.	20C3M	1870 – 1999
Year 2000 CO₂ maximum (Commit)	Atmospheric CO₂ concentrations are held at year 2000 levels. This experiment is based on conditions that already exist (e.g., “committed” climate change). Details	Commit	2000 – 2100
550 ppm CO₂maximum (SRESB1)	Atmospheric CO₂ concentrations reach 550 ppm in the year 2100 in a world characterized by low population growth, high GDP growth, low energy use, high land-use changes, low resource availability and medium introduction of new and efficient technologies.	SRESB1	2000 – 2100
720 ppm CO₂ maximum (SRESA1B)	Atmospheric CO₂ concentrations reach 720 ppm in the year 2100 in a world characterized by low population growth, very high GDP growth, very high energy use, low land-use changes, medium resource availability and rapid introduction of new and efficient technologies.	SRESA1B	2000 – 2100
850 ppm CO₂ maximum (SRESA2)	Atmospheric CO₂ concentrations reach 850 ppm in the year 2100 in a world characterized by high population growth, medium GDP growth, high energy use, medium/high land-use changes, low resource availability and slow introduction of new and efficient technologies.	SRESA2	2000 – 2100
Geography	Geographic information about each grid-cell*	NA	NA

*Are these data identical to those used for the Fourth IPCC assessment?

The data distributed by EOS-WEBSTER have been modified from the original used in the 4th IPCC assessment. These modifications were made to improve ease of using the data and do not alter the results predicted by the models. Modifications include a small change in the shape and size of the global grid. Originally, the data were on a gaussian grid of 1.40625 degrees longitude centered at the prime meridian (0 degrees longitude), with latitudes of 1.40625 degrees at the equator getting farther apart towards the poles. For our GIS-friendly version of these data, we have recast the grid cells onto a regular, 1.40625 deg longitude x latitude grid starting at -180.0 degrees longitude and 90.0 degrees latitude, which results in a slight shift of the grid cells. The actual grid cell center points and areas can be obtained from the collection by ordering the geography file.

This global grid shift is depicted in this diagram:

If you plan to use these data in peer-reviewed, scientific journal articles, please use the information in the geography file to precisely georeference the data and correctly calculate the area of each grid cell.

Variables available from the NCAR/IPCC 4th Assessment Report Climate Change Data collection:

Variable name *(CF standard_name)**	Short name, used to name EOS-WEBSTER output files	Units	Description
air_pressure_at_sea_level	psl	Pa	The pressure exerted by the atmosphere at sea level due to the weight of the air. Sea level is defined as close to the geoid in sea areas.
air_temperature	tas	K	The bulk temperature of the air measured near surface at 2 m; not the surface (skin) temperature.
atmosphere_cloud_condensed_water_content	clwvi	kg m^-2	Mass of all condensed water, both liquid and ice phases, in the column from the surface to the top of the atmosphere, divided by its area (in the longitude-latitude plane).
atmosphere_cloud_ice_content	clivi	kg m^-2	Mass of condensed water in the column from the surface to the top of the atmosphere divided by its area (in the longitude-latitude plane).
atmosphere_water_vapor_content	prw	kg m^-2	Sometimes referred to as "precipitable water" vertically integrated through the atmospheric column, although this term does not imply the water could all be precipitated.
cloud_area_fraction	clt	%	Fraction of horizontal area occupied by clouds including both large-scale and convective cloud. Also called "cloud amount" and "cloud cover". The cloud area fraction is for the whole atmosphere column, as seen from the surface or the top of the atmosphere.
convective_precipitation_flux	prc	kg m^-2 s^-1	Precipitation particles forming in the active updraft of a cumulonimbus cloud growing primarily by the collection of cloud droplets (by coalescence and/or riming) and falling out not far from their originating updraft.
eastward_wind	uas	m s^-1	Eastward component of wind near-surface at 10 m. Wind is defined as a two-dimensional (horizontal) air velocity vector, with no vertical component.
moisture_content_of_soil_layer	mrsos	kg m^-2	Water in all phases (moisture), in the upper 0.1 meters of soil and averaged over the land portion of the grid cell computed by dividing the total mass of water contained in the soil layer of the grid cell by the land area in the grid cell; reported as "missing" or 0.0 where the land fraction is 0.
net_downward_radiative_flux_at _top_of_atmosphere_model	rtmt	W m^-2	Sum of shortwave and longwave radiative fluxes at the top of that portion of the atmosphere where dynamics are explicitly treated by the model. Fluxes at the top_of_atmosphere_model differ from TOA fluxes only if the model TOA fluxes make some allowance for the atmosphere above the top of the model; if not, it is usual to give standard names with toa to the fluxes at the top of the model atmosphere.
net_downward_shortwave_flux_in_air	rsntp	W m^-2	The difference between shortwave radiation from above (downwelling) and from below (upwelling) at 200 hPa only.
net_downward_shortwave_flux_in_air _assuming_clear_sky	rsntpcs	W m^-2	The difference between shortwave radiation from above (downwelling) and from below (upwelling) assuming clear sky conditions at 200 hPa only.
net_upward_longwave_flux_in_air	rlntp	W m^-2	The difference between longwave radiation from below (upwelling) and from above (downwelling) at 200 hPa only.
net_upward_longwave_flux_in_air _assuming_clear_sky	rlntpcs	W m^-2	The difference between longwave radiation from above (downwelling) and from below (upwelling) assuming clear sky conditions at 200 hPa only.
northward_wind	vas	m s^-1	Northward component of wind near-surface at 10 m. Wind is defined as a two-dimensional (horizontal) air velocity vector, with no vertical component.
precipitation_flux	pr	kg m^-2 s^-1	Any form of water that falls from the atmosphere to the surface of the earth (liquid and solid phases such as rain, sleet, hail, and snow).
runoff_flux	mrro	kg m^-2 s^-1	Liquid water which drains from land, computed as the total runoff (including "drainage" through the base of the soil model) leaving the land portion of the grid cell divided by the land area in the grid cell; reported as "missing" or 0.0 where the land fraction is 0. If not specified, "runoff" refers to the sum of surface runoff and subsurface drainage.
snowfall_flux	prsn	kg m^-2 s^-1	Solid phase precipitation
soil_frozen_water_content	mrfso	kg m^-2	Amount of ice summed over all soil layers averaged over the land portion of the grid cell, computed by dividing the total mass of frozen water contained in the soil layer of the grid cell by the land area in the grid cell; reported as "missing" or 0.0 where the land fraction is 0.
soil_moisture_content	mrso	kg m^-2	Water in all phases, summed over all soil layers and averaged over the land portion of the grid cell computed by dividing the total mass of water contained in the soil layer of the grid cell by the land area in the grid cell; reported as "missing" or 0.0 where the land fraction is 0.
specific_humidity	huss	fraction	Mass fraction of water vapor in moist air near the surface at 2 m.
surface_air_pressure	ps	Pa	Pressure exerted by the atmosphere at the surface due to the weight of the air, but not mean sea-level pressure.
surface_downward_eastward_stress	tauu	N m^-2 (Pa)	Force per unit area that wind exerts on the surface. A downward eastward stress is a downward flux of eastward momentum, which accelerates the lower medium eastward and the upper medium westward.
surface_downward_northward_stress	tauv	N m^-2 (Pa)	Force per unit area that wind exerts on the surface. A downward northward stress is a downward flux of northward momentum, which accelerates the lower medium northward and the upper medium southward.
surface_downwelling_longwave _flux_in_air	rlds	W m^-2	Longwave radiation from above. When thought of as being incident on a surface, a radiative flux is sometimes called "irradiance". In addition, it is identical with the quantity measured by a cosine-collector light-meter and sometimes called "vector irradiance".
surface_downwelling_longwave _flux_in_air_assuming_clear_sky	rldscs	W m^-2	Longwave radiation from above. When thought of as being incident on a surface, a radiative flux is sometimes called "irradiance". In addition, it is identical with the quantity measured by a cosine-collector light-meter and sometimes called "vector irradiance".
surface_downwelling_shortwave _flux_in_air	rsds	W m^-2	Sum of direct and diffuse solar radiation incident on the surface, and sometimes called "global radiation". When thought of as being incident on a surface, a radiative flux is sometimes called "irradiance". In addition, it is identical with the quantity measured by a cosine-collector light-meter and sometimes called "vector irradiance".
surface_downwelling_shortwave _flux_in_air_assuming_clear_sky	rsdscs	W m^-2	Sum of direct and diffuse solar radiation incident on the surface, sometimes called "global radiation". When thought of as being incident on a surface, a radiative flux is sometimes called "irradiance". In addition, it is identical with the quantity measured by a cosine-collector light-meter and sometimes called "vector irradiance".
surface_runoff_flux	mrros	kg m^-2 s^-1	Liquid water which drains from land, computed as the total surface runoff leaving the land portion of the grid cell divided by the land area in the grid cell; reported as "missing" or 0.0 where the land fraction is 0. If not specified, "runoff" refers to the sum of surface runoff and subsurface drainage.
surface_snow_amount_where_land	snw	kg m^-2	Amount of snow on the ground, excluding that on the vegetation canopy, computed as the mass of surface snow on the land portion of the grid cell divided by the land area in the grid cell (mass per unit area); reported as "missing" or 0.0 where the land fraction is 0; excludes snow on vegetation canopy or on sea ice.
surface_snow_area_fraction_where_land	snc	%	Fraction of grid cell covered by snow that lies on land excluding snow that lies on sea ice.
surface_snow_melt_flux_where_land	snm	kg m^-2 s^-1	Total surface melt water on the land portion of the grid cell divided by the land area in the grid cell; reported as 0.0 for snow-free land regions; and as 0.0 or "missing" where the land fraction is 0.
surface_snow_thickness	snd	m	Depth of the snow layer. This thickness when multiplied by the average area of the grid cell covered by snow yields the time-mean snow volume.
surface_temperature	ts	K	Skin temperature at the interface, not the bulk temperature of the medium above or below.
surface_upward_latent_heat_flux	hfls	W m^-2	Exchange of heat between the surface and the air on account of evaporation including sublimation.
surface_upward_sensible_heat_flux	hfss	W m^-2	Exchange of heat between the surface and the air by motion of air, also called "turbulent" heat flux.
surface_upwelling_longwave_flux_in_air	rlus	W m^-2	Longwave radiation from below. When thought of as being incident on a surface, a radiative flux is sometimes called "irradiance". In addition, it is identical with the quantity measured by a cosine-collector light-meter and sometimes called "vector irradiance".
surface_upwelling_shortwave_flux_in_air	rsus	W m^-2	Shortwave radiation from below. When thought of as being incident on a surface, a radiative flux is sometimes called "irradiance". In addition, it is identical with the quantity measured by a cosine-collector light-meter and sometimes called "vector irradiance".
surface_upwelling_shortwave_flux_in_air _assuming_clear_sky	rsuscs	W m^-2	Shortwave radiation from below. When thought of as being incident on a surface, a radiative flux is sometimes called "irradiance". In addition, it is identical with the quantity measured by a cosine-collector light-meter and sometimes called "vector irradiance".
toa_incoming_shortwave_flux	rsdt	W m^-2	Incoming shortwave flux from the sun at the top of the atmosphere, often called downwelling TOA shortwave flux.
toa_outgoing_longwave_flux	rlut	W m^-2	Upwelling thermal radiative flux at the top of the atmosphere, often called the "outgoing longwave radiation" or "OLR". For comparison with satellite measurements.
toa_outgoing_longwave_flux_assuming _clear_sky	rlutcs	W m^-2	Upwelling thermal radiative flux at the top of the atmosphere assuming clear sky conditions, often called the "outgoing longwave radiation" or "OLR".
toa_outgoing_shortwave_flux	rsut	W m^-2	Reflected and scattered solar radiative flux at the top of the atmosphere, often called upwelling TOA shortwave flux, "outgoing shortwave radiation", or "OSR".
toa_outgoing_shortwave_flux _assuming_clear_sky	rsutcs	W m^-2	Reflected and scattered solar radiative flux at the top of the atmosphere assuming clear sky conditions, sometimes called the "outgoing shortwave radiation" or "OSR".

*CF is the NetCDF climate and forecast (CF) metadata convention. EOS-WEBSTER has retained the CF standard variable names for comparison with other IPCC data sets. See http://www.cgd.ucar.edu/cms/eaton/cf-metadata/ for more information about CF.

A searchable version of the standard name table is located at http://www.cgd.ucar.edu/cms/eaton/cf-metadata/standard_name.html .

Term usage:

Assuming _ condition, such as “assuming clear sky” - indicates that the named quantity is the value which would obtain if all aspects of the system were unaltered except for the assumption of the circumstances specified by the condition, in this case “clear sky”.

Content – "Content" indicates a quantity per unit area. The "atmosphere content" of a quantity refers to the vertical integral from the surface to the top of the atmosphere. For the content between specified levels in the atmosphere, standard names including content_of_atmosphere_layer are used.

Downward, Upward - "Downward" indicates a vector component that is positive increasing downward (negative upward); "Upward" indicates a vector component that is positive increasing upward (negative downward).

Eastward, Northward - "Eastward" indicates a vector component that is positive increasing eastward (negative westward); "Northward" indicates a vector component that is positive increasing northward (negative southward).

Flux - In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. Net downward, Net upward radiation - Net downward radiation is the difference between radiation from above (downwelling) and radiation from below (upwelling); Net upward radiation is the difference between radiation from below (upwelling) and radiation from above (downwelling).

Surface - The surface called "surface" means the lower boundary of the atmosphere; over sea areas this is taken to be mean sea level.

TOA – top of the atmosphere.

The IPCC Scenarios and Storylines: Special Report on Emissions Scenarios (SRES)**

By 2100 the world will have changed in ways that are hard to imagine - as hard as it would have been at the end of the 19th century to imagine the changes of the 100 years since. Each IPCC storyline assumes a distinctly different direction for future developments, such that the four storylines differ in increasingly irreversible ways. Together they describe divergent futures that encompass a significant portion of the underlying uncertainties in the main driving forces. They cover a wide range of key "future" characteristics such as population growth, economic development, and technological change. For this reason, their plausibility or feasibility should not be considered solely on the basis of an extrapolation of current economic, technological, and social trends.

* The A1 storyline and scenario family describes a future world of very rapid economic growth, low population growth, and the rapid introduction of new and more efficient technologies. Major underlying themes are convergence among regions, capacity building and increased cultural and social interactions, with a substantial reduction in regional differences in per capita income.

* The A2 storyline and scenario family describes a very heterogeneous world. The underlying theme is self-reliance and preservation of local identities. Fertility patterns across regions converge very slowly, which results in high population growth. Economic development is primarily regionally oriented and per capita economic growth and technological change are more fragmented and slower than in other storylines.

* The B1 storyline and scenario family describes a convergent world with the same low population growth as in the A1 storyline, but with rapid changes in economic structures toward a service and information economy, with reductions in material intensity, and the introduction of clean and resource-efficient technologies. The emphasis is on global solutions to economic, social, and environmental sustainability, including improved equity, but without additional climate initiatives.

** From the IPCC Special Report on Emissions Scenarios

Demographic, social, economic and technological profiles of the SRES scenarios:

Scenario Characteristics
Profile	SRESA1B	SRESA2	SRESB1
Population growth	low	high	low
GDP growth	very high	medium	high
Energy use	very high	high	low
Land- use changes	low	medium/high	high
Resource availability	medium	low	low
Pace of technological change	rapid	slow	medium

Source: http://www.grida.no/climate/ipcc/emission/091.htm

Schematic illustration of the SRES scenarios:***

The four scenario "families" are illustrated, very simplistically, as branches of a two-dimensional tree. The two dimensions indicate the relative orientation of the different scenario storylines toward economic or environmental concerns and global and regional scenario development patterns, respectively. There is no implication that these two are mutually exclusive or incompatible. In reality, the four scenarios share a space of a much higher dimensionality given the numerous driving forces and other assumptions needed to define any given scenario in a particular modeling approach. The schematic diagram illustrates that the scenarios build on the main driving forces of GHG emissions.