Welcome to CGD

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Science in CGD

1. Introduction

The Climate and Global Dynamics Division (CGD), which is part of the Earth and Sun Systems Laboratory (ESSL) at NCAR, strives to address fundamental scientific issues in Earth system science, with an emphasis on themes likely to benefit society through improved understanding of climate processes and advances in the science of climate prediction.

Specifically, the mission of CGD is to: (1) advance understanding of the Earth's climate system components and the interactions among them; (2) to represent this understanding in models of the components and of the coupled system; and (3) to further our understanding by applying the models to scientific and societal questions and thereby provide a basis for prediction of weather and climate. We fulfill this mission through a strong record of achievement in scientific research, community modeling and data set development. We are also very proud of our community service, leadership of national and international research programs, and educational and outreach activities. Accomplishments in these areas are detailed each year in our Annual Scientific Reports.

In addressing this mission, CGD contributes to the vision and mission of NCAR, as well as to the overarching goals articulated in the strategic plan of the National Science Foundation (NSF). As such, it helps NCAR to uphold a position of world leadership in science and technology, promoting the transfer of new knowledge to society, and contributing to excellence in science and technology education.

Our vision of CGD for the future is that it will address all aspects of its mission with an ambitious, effective, and aggressive scientific program of large scope and importance. A key aspect is a commitment to a world-class scientific and technical staff, representing true diversity in people, backgrounds, and ideas. A central aspect of our strategic plan, therefore, is to attract and retain leading scientists in the field and to develop the careers of young scientists toward leadership roles. To achieve this goal, we will respect scientific uniqueness and will promote collaboration and teamwork through maintenance of a congenial, supportive, and professional working environment.

Working with other academic institutions and with our colleagues within NCAR, CGD will continue to develop critically needed understanding of the Earth system and the human relationship with that system. CGD will continue in its role as a leader of community-developed and community-owned models of the Earth system. Such sophisticated models will provide the world's best theoretical understanding of coupled environmental systems, incorporating the relevant physical, chemical, biological, and human processes. CGD scientists will also continue in their leadership roles in national and international science planning and implementation, playing proactive roles in setting the research agenda to address the urgent problems facing our nation and the world. CGD will continue to move toward a more comprehensive Earth systems approach to integrative studies, including the human dimensions, and with an emphasis on bringing sound science to bear on societal decision making.

The following sections first provide an overview of the current scientific program of CGD, and then a discussion of the major scientific endeavors envisioned for the division over the next 5 years. This strategic plan is not an end point, but rather the beginning of a grassroots process to continually reevaluate and evolve the program in a strategic light.

2. Overview of the CGD scientific program

In order to appreciate the scientific goals of CGD over the next five years, as expressed in the next two sections, it is useful to briefly review the division's current research program. The program is evolutionary in nature, and there are many activities, but it can be summarized by the following two primary themes.

2.1 Development and Evaluation of Community Climate Models

The development and continuous improvement of a comprehensive climate modeling system that is at the forefront of international efforts to understand and predict the behavior of the Earth's climate continues to be a high priority of CGD research. This includes the Community Climate System Model (CCSM) as well as its component models, the Whole Atmosphere Community Climate Model (WACCM), and some models of intermediate complexity. Fundamental research on climate processes operating in the atmosphere, ocean, land and cryosphere is required for model development, both through the improvement of the physical representation of climate processes and through the introduction of representations for missing physical processes. Climate process research also provides a framework for climate model experiments, as well as for deciding which observations to analyze. Included, for instance, is basic research on chemistry and climate, aerosols, clouds and convection, the global carbon, nitrogen, water and energy cycles, ocean and atmospheric eddies, snow and ice, dynamic vegetation, and land cover and land use change.

Improvements in the physics and software continue to expand the range of scientific applications for the CCSM. CGD software engineers and scientists, with external collaborators, continue to improve model coding structures, expand the computer hardware suitable for model applications, provide tutorials on how to download, build and execute the model, document the model, and incorporate the Earth System Modeling Framework (ESMF) into the latest version of CCSM. They are also involved in the distribution of simulations for the present climate and recent past using the new Earth System Grid (ESG) developed by SCD and collaborators from the Department of Energy (DOE). CCSM liaisons provide critical links to university partners and support the research of the external community. The annual CCSM user workshop requires considerable planning and support as attendance increases every year, exceeding 330 participants in both 2004 and 2005.

Currently emphasis is being placed on reducing systematic biases that plague CCSM (and many other coupled models), such as the notorious biases associated with the double Inter-Tropical Convergence Zone (ITCZ), the warm sea surface temperature (SST) biases under the stratocumulus regions off the west coasts of North America, South America and Africa, errors in the simulated intraseasonal and interannual variability of the tropics, and various regional biases in simulated rainfall and surface temperature. The reduction of such biases becomes even more important as the complexity of CCSM increases, for instance through the introduction of dynamic vegetation. Several hypothesis-driven activities are underway in collaboration with colleagues outside of NCAR to address such biases, including new collaborative efforts within ESSL to examine, in climate simulations with embedded regional models, the importance of explicitly resolving mesoscale and microscale processes that govern weather and local climate but that may also have significant impacts on the large-scale circulation.

The development and evaluation of community models directly supports the NCAR mission through the creative involvement of university and government researchers and students, nationally and internationally, in the design, construction, evaluation and use of community climate models, most notably the CCSM. The CCSM is also an important component of the overall U.S. Climate Change Science Program (CCSP), and through application of the modeling system NCAR is a major contributor to the assessments of the Intergovernmental Panel on Climate Change (IPCC). Using CCSM as a common numerical framework, interdivisional development of the WACCM continues the evolution toward a complete Earth system modeling capability at NCAR.

2.2 Climate Analysis: Diagnostic, Theoretical and Modeling Studies

A goal of this high priority CGD research is to increase our understanding of atmospheric and climate variability and climate change through parallel development and analysis of observational, assimilated, model-generated and model-forcing datasets; and, by using these datasets for empirical studies, diagnostic analyses, and model experimentation to document comprehensively climate variability, its causes and the processes involved. Further, systematic numerical experimentation using models provides insights and assesses predictability that may allow attribution of observed variability to processes and causes.

Exploring climate, climate variability and climate change with observations, and applying both observed and model-generated datasets for diagnostic studies of attribution of the climate state on multiple time scales is a high priority of CGD research. Work in this area includes analysis of the global water, heat and energy cycles, phenomenological studies of dominant modes of climate variability such as the El Niño-Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO) and Tropical Atlantic Variability (TAV), attribution of observed ocean, atmospheric, and cryospheric variability to processes and causes, and examinations of the dependencies between climate and land cover and land use change.

CGD scientists are also heavily involved in national and international efforts designing and advocating the global climate observing system, institutionalizing reanalysis, and articulating the need for and benefits of a climate information system. This involvement has stemmed directly from core climate analysis research that has revealed limitations in current observing systems and the data they produce. CGD is leading in the development of data assimilation techniques for biogeochemistry and carbon cycle studies. This diagnostic capability is especially important as coupled carbon-climate capabilities come on line in the CCSM.

Investigations of predictability and the determination of appropriate measures of inherent uncertainty associated with chaotic aspects of the climate system provide the scientific basis for projecting transient, global circulations in the atmosphere beyond present practical limits. Within CGD, research in predictability involves: (1) numerical and theoretical experimentation with a hierarchy of physical models; (2) analyses of theoretical and practical predictability in simulation and forecast experiments using the Community Atmospheric Model (CAM) and CCSM; and (3) sensitivity analyses of numerical prediction models to atmospheric initial and boundary conditions using variational and ensemble techniques.

Paleoclimate research within CGD is centered on studies of deep time, the past 150,000 years, and the past millennium. The boundary between the Late Permian and Triassic periods marks the largest extinction recorded in Earth's history, and CGD researchers are carrying out the first fully coupled climate simulation for this period using CCSM. Considerable efforts are also placed on simulating and constructing high-resolution paleoclimate records of climate variability and abrupt climate change over more recent periods. CCSM simulations of the last millennium are key to understanding the roles of natural and anthropogenic forcings in the observed climate record.

Through application of the climate modeling system in CGD, NCAR is a major contributor to the assessments of the IPCC. Currently emphasis is on the detailed analysis of the CCSM simulations produced for the IPCC Fourth Assessment Report (FAR) for a wide range of studies of climate variability and climate change. Diagnostic studies of observed and model-generated datasets for climate change issues are also a high priority.

Data analysis and interpretation, the development of community data sets, and application of theoretical, conceptual and community climate models for studies of predictability, climate variability and climate change on all time scales are key components of the NCAR mission. Moreover, climate analysis research in CGD directly addresses priority areas in many national and international programs, and CGD scientists provide strong leadership in these programs. Examples include CCSP, Global Energy and Water Cycle Experiment (GEWEX), Climate Variability and Predictability (CLIVAR), Past Global Changes (PAGES), IPCC, Global Climate Observing System (GCOS), International Geosphere-Biosphere Programme (IGBP), and the World Climate Research Programme (WCRP) as a whole. Climate analysis research involves strong collaborations across NCAR, including leadership in NCAR strategic initiatives, as well as strong ties to many university scientists and researchers at national laboratories around the world.

CGD will maintain a vital core program in the areas mentioned above; yet, the program will evolve in time as called for by scientific priorities. In the next sections, we express a vision for the main scientific thrusts of the division, in collaboration with its university partners and other collaborators.

3. Understanding of Past, Present and Future Climate

The internal interactive components of the climate system include the atmosphere, oceans, sea ice, land, snow cover, land ice, and fresh water reservoirs. The greatest variations in the composition of the atmosphere involve water in various phases (water vapor, clouds of liquid water, ice crystal clouds, and rain, snow, and hail); however, other constituents of the atmosphere and the oceans can also change, thereby bringing considerations of atmospheric chemistry, marine biogeochemistry, and land surface exchanges into climate change. Moreover, external effects, such as changes in solar activity, volcanic eruptions, and human influences, influence the climate system. Understanding the forcings of the climate system, how the components interact, and the processes involved, and developing the ability to model these and predict the future are major challenges central to the CGD program.

3.1 Climate Forcings

Understanding radiative forcing is necessarily a basic step in the study of climate. To first order, the energy that is entering the Earth system is balanced by the amount that is lost to space. Any change to this balance acts as a forcing on the system resulting in a change to the climate through a redistribution of energy between its different components. While modifications to the Earth's radiative balance can result from feedbacks and interactions within the coupled climate system, the most significant forcings with impact on climatic time scales are generally imposed upon the system.

External forcings arise from a wide array of processes covering a range of spatial and temporal scales. They include changes in the global configuration of the continents or the slow increase of solar luminosity that occur over hundreds of millions of years to the local emission and suspension of small particles on timescales of minutes to days. Additionally, feedbacks from changing greenhouse gases and secondary aerosol regulated by atmospheric chemistry and changes in biogeochemical cycles can lead to a complex response of the overall system. While uncertainty from some of the more slowly changing forcings is quite high because measurements to describe the forcing changes are lacking, the very short term and spatially heterogeneous forcings, particularly from aerosol and aerosol-cloud interactions are poorly understood and extremely difficult to resolve in models.

CGD's focus on radiative forcing can be summarized by two primary goals: (1) to advance the physical understanding of the processes that cause changes to the radiative forcing; and (2) to use the improved knowledge for a better quantification of these processes through increased resolution or advanced parameterizations in models. Key research areas guided by these goals are:

Variations of the solar input (irradiance) have only been accurately measured for a few decades. Various estimates of how the sun is varying today and has changed in the past have to be evaluated in order to capture the full range of this natural forcing. This includes feedbacks from climate dynamics, upper atmosphere ozone-temperature feedbacks and changes in the components of solar irradiance. These studies require and will proceed through collaboration among CGD, HAO and ACD.

Aerosols and dust or their precursors that are emitted into the atmosphere by both natural and anthropogenic mechanisms are another important climate forcing. Natural emissions include volcanic eruptions and dust storms, and an anthropogenic emission is the increased pollution due to industrialized sources. Advances in the understanding of physical processes are required in the field of small particles, how and where they are formed, transported and removed from the atmosphere, how they affect radiation, and how they interact with the water cycle and affect atmospheric chemistry. These are highly interdisciplinary questions that need to be approached on local and global scales in collaboration with ACD, MMM, TIIMES and EOL.

In addition to other anthropogenic forcings such as changes to the chemical composition of the atmosphere, historical changes in land use and changes in the distribution of continental water due to dams and irrigation need to be considered. Future projected land cover changes due to human land uses are also likely to significantly affect climate, and these effects are only now being included in climate models such as the CCSM.

3.2 Natural Variability

The climate system varies naturally on multiple timescales, as evidenced by many observations and analyses of the past climate, including paleoclimate. A key activity in understanding natural variability is the development of theoretical and conceptual models of the processes that give rise to natural variability. A crucial question is how well do we understand and simulate the full spectrum of natural variability in models, confirming that we have represented appropriately the driving processes? The ability to simulate the variability is necessary to provide a sound basis for future projections. Simulating variability also requires proper recognition predictability to determine appropriate measures of inherent uncertainty associated with chaotic aspects of the climate system.

Global surface temperatures in recent years have not warmed uniformly even as global warming progresses (Fig. 1). Why is this? Over the oceans the temperature change pattern reflects differences in regional coupling to the atmosphere, and it relates to the uptake of heat and the resulting ocean heat content and transport. The tropical Indian Ocean has steadily increased in temperature to be as warm as the so called Warm Pool in the tropical western Pacific, heretofore the warmest part of global ocean and thus of greatest atmospheric influence. The Pacific pattern of warming in the tropics and cooling in the North Pacific is identified with changes in statistics of ENSO and the related Pacific Decadal Oscillation. The associated changes in atmospheric circulation also explain why some of the largest continental warming occurs over Alaska. Deeper ocean mixing occurs in the Atlantic, giving rise to the predominant thermohaline circulation in the ocean. The pattern of trends there could relate to a slowing of this circulation, and idea supported by observed changes in salinity in the Atlantic. Also cooling over northeast Canada and enhanced warming over Eurasia are linked to wintertime tendencies for increased frequency of the positive phase of the NAO that in turn may be linked to warming in the tropical Indian and Pacific Oceans. These unique aspects of the various oceans and their consequences for sea surface temperatures (SSTs) lead to patterns not yet well simulated by coupled models. Yet the hypothesis is that they are predictable if the models become good enough.

The research program to address these issues necessarily involves many parts, including:

• Exploring climate, climate variability and climate change through the development, evaluation and analysis of observational, assimilated and model-generated data sets, including satellite data and reanalysis products.

• Empirical studies, diagnostic analyses, and model experimentation to document comprehensively climate variability, its causes and the processes involved.

• Attribution studies of the climate state on multiple time scales, and especially large anomalies in climate (e.g., a devastating heat wave or drought), to changes in external (e.g., solar, volcanoes, atmospheric composition) and internal (e.g., ENSO, ocean heat content, sea ice, soil moisture) forcing and the role of natural (essentially unpredictable) variability.

• Development of theoretical and conceptual models that form the basis of our understanding of natural variability.

• Studies to assess predictability limits for the climate system in order to help develop predictive capabilities on multiple time-scales. Predictability experiments deal with the fundamental problem of how to initialize ocean models and other parts of the climate system, and the results of such experiments are also pertinent to how to validate models using large ensembles.

• Investigations of the physical basis of biases in coupled model simulations of the climate system, such as those from CCSM. An accurate representation of the mean climate, its annual cycle and the variability of the coupled system is necessary in order to predict natural climate variability and understand the climate system's sensitivity to external forcing.

• Studies to assess the reliability of observations and evaluate the state of the observing system, including the adequacy of observations for monitoring the climate system, for detecting and attributing climate change, for assessing the impacts of climate variability and change, and for supporting research toward improved understanding, modeling and prediction of the climate system.

3.3 Feedbacks

The response of the climate system to forcing is modulated by its climate sensitivity. If the climate system is highly sensitive, then a small forcing will produce a proportionately larger response than a system with low climate sensitivity. Understanding the Earth's climate sensitivity is a grand challenge problem for the geosciences. Models have been used to consider the equilibrium global warming due to a doubling of carbon dioxide. Results from this approach indicate a warming of 3°C with a range of about 1.5°C. Various feedback processes operating in the climate system determine the magnitude of the climate sensitivity. In the atmosphere these processes include changes to the hydrologic cycle, especially changes in water vapor and cloud properties. Changes in atmospheric chemistry can also feedback to the physical climate system. In the oceans feedback processes include the efficiency of ocean mixing and changes in sea ice properties. Over land feedbacks involve changes to surface cover, albedo, evapotranspiration, runoff and biogeochemical cycles. Each of these components is a part of Earth's climate system and thus the study of climate sensitivity or feedback processes serves as an integrator of knowledge of Earth as a system.

CGD is poised to make major contributions to the understanding of climate feedbacks through a synergistic interactive use of observations, modeling and theory. In terms of atmospheric processes over the next few years new satellite data will be available to study high-resolution cloud processes on a global scale. Observations of aerosol processes will also enable a more detailed understanding of their effects on the hydrologic cycle. For the ocean, a new array of floats and other observing platforms offer the opportunity for a more comprehensive view of the ocean's thermal and dynamical structure. Over land, satellite data provide a means to monitor land cover change, leaf area index, vegetation activity, biomass burning, snow cover, soil moisture, albedo, and radiometric surface temperature. Paleo proxy data are also being refined to include more geographic regions and longer high-resolution temporal records and consider new processes. Also, reanalysis products will continue to improve and become more comprehensive in terms of spatial resolution and temporal length. All of these data products offer unique opportunities to look at Earth's system in a more detailed and integrated fashion. The challenge is how to use these data to deepen our understanding of the various feedbacks in the climate system.

Using the CCSM and its components to simulate the climate system for past, present and future time periods provides a rich source of information on how feedbacks may operate in the real world. These feedbacks depend strongly on sub-grid scale parameterizations that need to be validated against observations on a wide range of space and time scales. One advantage of modeling is that specific feedback mechanisms can be studied in detail. Although many of these data and model simulations have existed in the past, what is required is more synergistic interactions among those that analyze climate data and those who model the climate system. Specific research questions can help focus CGD's efforts on increasing our understanding of feedbacks and climate sensitivity, for example:

• How does intra-annual to decadal variability depend on the magnitude and sign of climate feedback mechanisms?

• How do cloud feedbacks operate in the present day world on diurnal to seasonal time scales?

• How does ocean mixing change in a warmer greenhouse world?

• How do biogeochemical cycles operate in the present day world, and how will they change in a warmer greenhouse world?

• What can glacial and interglacial climates tell us about climate feedbacks?

• Are there theoretical limits to the magnitude of certain feedback mechanisms?

These questions lead to scientific hypotheses that focus scientists to use synergistic approaches that combine observations, models and theory within CGD. A concerted effort will be made to reach out to the observational community to create strong collaborative ties to include these scientists in the teams focused on testing specific hypotheses. CGD can act as a center of renewed activity on climate feedback research. Given its expertise in climate analysis and modeling, it is well poised to provide the leadership in improving our understanding in this critical climatic factor.

a. Atmosphere Process Research

An understanding of the past, present and future climate requires a thorough understanding and accurate representation of a variety of atmospheric processes. Clouds and precipitation, and in particular the feedback of clouds on climate through radiation, are among the most important processes. Clouds also play a central role in the transport and chemical transformation of minor constituents (including moisture as well as chemical constituents) and, through their influence on radiative properties at the surface, they strongly interact with the other components of the climate system.

Over the next several years CGD research will focus on understanding how cloud feedbacks affect the Earth's climate. Clouds play a fundamental role in determining the radiative and chemical balance in the atmosphere, as sites for the photochemical production and loss of constituents, as agents for rapid transport of species from regions near the surface to high altitudes, and in diabatic heating of the atmosphere through latent heat release associated with the conversion of water vapor to precipitation. Indeed, many of the processes that influence Earth's "climate sensitivity" as a system are integral parts of the global energy and water cycle.

The atmosphere acts as a reservoir, conduit and chemical processor for trace (gaseous and aerosols) constituents. These trace constituents influence the radiative balance of the atmosphere and thus influence the evolution of the past, present and future climate. The atmosphere also provides the primary means for coupling between different components of the climate system (land, ocean, cryosphere) through exchanges of heat, moisture, momentum, and other chemical and aerosol constituents via complex atmospheric boundary layer mechanisms.

For these reasons, some of the research on atmospheric processes within the division will be oriented on two activities. First, improving representations of cloud and water substances in the atmosphere, the processes that interact strongly with them (like aerosols and radiation), and their influence on and interactions with other components of the climate system. This will involve improved parametric treatments of boundary-layer exchanges that deal with phase and chemical transitions more comprehensively, moist convection in terms of its initiation, temporal characteristics and interaction with stratiform cloud processes and the large-scale cloud field, and improved and more flexible treatments of radiative transfer. The treatment of large-scale cloud processes will require generalization to allow a tighter coupling with aerosol processes and a comprehensive and realistic investigation of the indirect effect. A more comprehensive treatment of the atmospheric momentum budget will also be required in the form of improved representations of momentum transport by clouds, including the generation of vertically propagating gravity waves by vigorous convection.

A second, but tightly coupled focal point, will be on improving the representation of transport processes in the atmosphere, and understanding and representing the mechanisms by which the atmosphere communicates with other components of the climate system. Principal examples are exchange and transport properties in the atmospheric boundary layer, transport in the free atmosphere involving water phase change processes, removal mechanisms in clouds, and the detailed interaction of radiation processes with the surface components of the climate system (e.g., solar radiative heating of the ocean mixed layer). Opportunities to evaluate and improve the treatment of atmospheric transport will come from the incorporation of passive tracer information in parameterized processes. Isotopes provide an example of one of the most useful means for understanding complex processes in the atmospheric water cycle, biogeochemistry and chemistry on many time scales. Emphasis will be placed on the inclusion of isotope and other passive tracer data to provide a better basis for identifying the strengths and weaknesses of parameterized transports in the atmosphere.

This will necessitate the continued development of collaborations with scientists in the university community, as well as collaborations with scientists across NCAR, from ACD, MMM, EOL, RAL, TIIMES, and others.

b. Land Process Research

The land surface affects climate through a variety of ecological, hydrological, and biogeochemical processes. Terrestrial biogeochemistry and the fluxes of carbon, nitrogen, mineral aerosols, and biogenic aerosols between land and atmosphere are a dominant area of CGD terrestrial science research. Land use and land cover change are other important processes that can affect climate. Scientists also study the terrestrial hydrologic cycle and its feedback on the atmosphere.

The role of the terrestrial carbon cycle as a feedback in the climate system is a primary focus of terrestrial science research in CGD. This research includes the development, evaluation, and application of fully interactive climate-carbon simulations in the CCSM. The objectives are to better understand: (1) what processes and feedbacks are most important in setting atmospheric carbon dioxide, and (2) how may the carbon dioxide growth rate and climate change co-evolve in the future. Terrestrial and oceanographic carbon cycle models coupled into the CCSM will be used to study the evolution of carbon dioxide from pre-industrial times to the future. Significant mobilization of mineral aerosols in marginal arid lands impacts the atmospheric radiative budget, atmospheric chemistry, and terrestrial and ocean biogeochemistry. Iron deposited into the oceans through mineral aerosols is thought to be an important modulator of ocean biogeochemistry. The amount of mineral aerosols in the atmosphere varies by a factor of three to four times globally between glacial and interglacial time periods, and regionally between the present and six thousand years ago. These large changes in mineral aerosols indicate not only substantial changes in vegetative cover and aridity, but also in radiative forcing. The inclusion of mineral aerosols into CCSM allows the important paleoclimate problem of glacial-interglacial fluctuations in carbon dioxide, which are likely partly driven by changes in mineral aerosols, to be addressed.

These climate model experiments require integrating traditional hydrometeorological land surface models with models of the terrestrial carbon cycle and vegetation dynamics. Carbon model development includes litter and soil organic matter dynamics, nitrogen constraints for carbon assimilation and allocation, competition between plants and soil biota for soil mineral nitrogen resources, competition among plant functional types for common soil water and mineral nitrogen resources, and interactions between plant community disturbance processes and age structure. The coupled carbon-nitrogen model depends on a specification of mineral nitrogen deposition from the atmosphere. In collaboration with ACD, a preliminary offline coupling has been established to provide this field as an output from atmospheric chemistry simulations being developed within the CCSM atmosphere component, with the eventual aim of fully coupled nitrogen deposition from the atmosphere and emissions from the land surface. The terrestrial carbon cycle model also includes biomass burning and its effect on the age structure of terrestrial ecosystems. Additionally, biomass burning in tropical and boreal forest regions releases black and organic carbon aerosols to the atmosphere, both of which are radiatively important and may impact cloud properties and snow albedo.

A major research focus for terrestrial science is natural and human-mediated changes in land cover and ecosystem functions and their effects on climate, water resources, and biogeochemistry. Change in land cover from human uses of land is increasingly being recognized as an important forcing of climate. The influence of historical land cover change on climate needs to be considered as a climate forcing in addition to traditional forcings such as greenhouse gases, aerosols, solar variability, and ozone. Future projected land cover changes due to human land uses are also likely to alter climate, especially in the tropics, subtropics, and semiarid regions. Scientists in CGD have initiated a study of the global climate forcing associated with land use. This work has the goal of assessing: (1) how changes in land use and land cover have altered present-day climate and are likely to alter future climates, and (2) the importance of the land use and land cover change forcing relative to other IPCC SRES forcings. In addition to human-mediated land use changes, large-scale changes in the geographic distribution of vegetation as a result of past and future climate changes alter climate. Study of these coupled climate-vegetation dynamics requires a model that simulates vegetation biogeography in response to prevailing climate. This model will be applied to study the contribution of vegetation to climate sensitivity.

The role of the terrestrial hydrologic cycle as a feedback in the climate system is being investigated at two timescales. Of particular interest at the seasonal-to-interannual time scale is to understand the hydrological and meteorological processes by which soil moisture affects precipitation anomalies. Critical research pathways include gaining better insight into the diurnal cycle of the atmospheric boundary layer and land surface, and improved understanding of the terrestrial hydrologic cycle, especially the processes that affect soil moisture and the effect of soil moisture on latent heat flux. At the time scale of decades to centuries, studies suggest that summer soil moisture in the interior of Northern Hemisphere continents will decrease over the next century as the concentrations of greenhouse gases in the atmosphere increase, thereby increasing the risk of drought. However, assessment of future drought susceptibility is complicated by the sensitivity of the climate models to, among others, their parameterization of the land surface and the hydrologic cycle. A central science question for drought research is to determine the role of vegetation in exacerbating or ameliorating drought severity.

c. Ocean Process Research

The ocean is the flywheel of the climate system because its heat capacity is huge compared to the atmosphere, land and sea ice. Thus, the rate at which the ocean takes up heat is very important in determining the rate at which the surface atmosphere warms or cools. In addition, about 25% of the carbon dioxide emitted into the atmosphere since the industrial revolution has been taken up by the ocean. Thus, the ocean is very important in determining how much carbon dioxide remains in the atmosphere. Will this carbon uptake remain constant if the surface ocean warms, as it is predicted to do in the future? CGD will retain its focus on the ocean processes that are important in setting the rate of heat and carbon uptake into the global ocean.

Most of the heat and carbon dioxide is taken up in the upper ocean boundary layer. CGD will continue research into the processes that determine the depth and annual cycle of the upper boundary layer. A new thrust is focusing on vertical mixing, and the role of meso-scale eddies in extracting energy from the wind and making it available for mixing, while another is investigating eddy-mixed layer interaction as part of the CLIVAR Climate Process Team on the interaction between eddies and the boundary layer.

CGD will improve the tropical variability at all time scales from the daily to the mean in the CCSM. It is very important that the CCSM has realistic ENSO variability in order that scenarios of the future using the model are reliable. Therefore, a research focus on oceanic processes is being initiated, which will include tropical instability waves, subtropical and tropical cell interactions, and atmospheric coupling from the diurnal to seasonal cycle.

Heat is taken into the deep ocean in deep water formation regions that, along with density changes from rainfall and salinity, drive the thermohaline circulation (THC). Investigations into this mechanism will focus on the processes that link the circulation to the atmosphere and especially large scale modes of climate variability such as the Southern Annular Mode and the North Atlantic Oscillation, and the processes involved in the gravity current entrainment of deep overflows in the ocean. The last process is part of the CLIVAR Climate Process Team on gravity current entrainment.

CGD and collaborators from several institutions are developing a comprehensive ocean ecosystem module. It includes multiple phytoplankton groups, nitrogen fixation, limitations because of major nutrients, and treatments of sinking and remineralization of biological material. Initial tests of this module in fully coupled carbon cycle integrations have yielded realistic results, and this module will be brought into the updated CCSM framework in the near future.

d. Cryosphere Process Research

Research efforts within CGD and in collaboration with scientists at other institutions will focus on a number of issues related to cryospheric feedbacks and the role of the cryosphere in the global climate system. The first is polar amplification. Climate change simulations show amplified warming at high northern latitudes, largely due to surface ice-albedo feedbacks. However, the range of warming projections in the Arctic is larger than anywhere else on the globe, suggesting that the simulation of polar feedbacks varies considerably between different models. Compared to other models, the CCSM has anomalously high simulated polar amplification. Previous studies have related this amplified response to control climate sea ice conditions. In particular, models with thinner Arctic sea ice cover in control simulations tend to simulate high polar amplification as the thin ice is easily melted away producing larger changes in surface albedo. However, while the relatively thin ice cover in the CCSM2 control simulation might partially account for the high simulated polar amplification, the CCSM3 has considerably thicker sea ice and yet a higher simulated polar amplification. This suggests that other influences on the surface albedo feedback, including how clouds change, or other feedbacks in the CCSM modify the polar amplification signal. In order to understand these influences and their interrelations, both modeling and observational efforts are needed. These should help elucidate the strength of the surface albedo feedback and its role in climate variability and change. Additionally, this will help to improve its simulation in climate models.

The second is the role of the cryosphere in thermohaline circulation variability and change. The subpolar North Atlantic is a major deep water formation site for the global ocean. Previous observational and modeling studies have indicated that variations in sea ice transport into this region have the ability to modify deep water formation and as a consequence, the THC. More specifically, modeling studies have shown that increased ice export leads to more ice melt in the sub-polar North Atlantic. This increases the ocean stability causing decreased deep water formation. Modeling studies examining these effects have often used rather coarse resolution or intermediate complexity systems. Further efforts are needed to understand the implications that changes in sea ice and glacier mass budgets have for the THC strength. In particular, studies are needed to examine these effects in coupled models such as the CCSM, to understand the role of the cryosphere in THC changes under global change scenarios, and to examine the role of changes in glacier and ice sheet mass budgets on the THC. Many of these studies require model control and sensitivity simulations. The planned incorporation of an ice sheet model into future versions of the CCSM will allow the examination of the coupled interactions of ice sheet and THC changes.

3.4 Climate Responses

a. Past Climate

Paleoclimates offer a unique perspective to understand both the Earth's climate sensitivity and stability. Proxy climate indicators reveal reduced equator-to-pole temperature gradients in warm greenhouse climates, dramatic variations in atmospheric CO2 and methane contents and continental ice sheets, and rapid reorganizations of the climate system. Using paleo proxy data in conjunction with the CCSM can provide valuable information to test our understanding of the Earth's climate system, both the physical and biogeochemical components. Key questions remain on the sensitivity of the climate system, the strength of feedback processes and regional responses, which will be investigated using CCSM for the full range of past climates. These studies will help constrain estimates of future climate sensitivity.

Significant changes in Earth's climate have occurred on geologic time scales. It is often thought that these changes occurred on relatively slow time scales, but there are a number of cases where change occurred on relatively fast geologic time scales (~1,000 to 10,000 years). The current hypothesis for the rapid warmth of the Late Paleocene Thermal Maximum (~55 million years ago) is that large emissions of methane from methane hydrate deposits at the base of the coastal regions over a very brief period (~1000 years) caused excursions in carbon and added to global warming. The additional carbon to the climate system is roughly two to three times the amount of CO2 that will be added to the atmosphere over the next century assuming a business-as-usual emissions scenario. CCSM simulations will be used to quantify the climate sensitivity of the model for high levels of carbon dioxide and methane.

The primary external forcing over the last 1.6 million years (the Quaternary) was the variations of the incoming solar radiation caused by changes in the Earth's orbital character. This cyclic forcing, termed Milankovitch, with periods of 23,000, 41,000, 100,000 and 400,000 years, is not sufficient to explain the large excursions of climate and waxing and waning of massive continental glaciers during this period, nor the saw-tooth patterns with rapid transitions occurring on time scales as short as decades. Greenhouse gas concentrations (CO2 and CH4) and dust as measured in ice cores show a remarkably similar pattern to temperature over the last 400,000 years. CCSM simulations will be used to define the tropical-middle latitude-polar and land-ocean responses to changing greenhouse gases, aerosols, seasonal solar radiation, and vegetation-ice sheets for glacial and interglacial periods. Sensitivity simulations for the last glacial period will evaluate the scaling of the response of CCSM to increases/decreases in atmospheric CO2.

Since the dawn of human civilization some 10,000 years ago, climate has varied considerably, but not as dramatically as during the preceding glacial period. Driven by a combination of variations internal to the climate system as well as through external forcings, ranging from short-term volcanic perturbations to slow shifts in the orbital configuration, these historical climate fluctuations represent an important measure of natural climate variability. Coupled climate model experiments with a carefully selected subset or the full set of estimated forcing histories provide insight into the time dependent evolution of climatic changes as they are linked to external forcing. Of particular interest are the most recent periods for which high-resolution proxy data are available to evaluate the model results. Simulations of the past millennium should include the latest estimates of radiative forcings as well as previously unresolved factors such as human land use changes and changes in seasonality of insolation. The role of possible thresholds in climate change is of particular interest for the process of predicting future climate changes. Thus, the most recent natural events need to be understood. A fully coupled carbon cycle and a stable isotope model can provide an important measure of the merit of such simulations.

b. Abrupt Climate Change

The glacial-interglacial cycles include abrupt reorganizations of the climate system in as short of a period as decades to centuries. The record shows rapid shutdowns of the North Atlantic overturning circulation, through freshwater impulses from melting Northern Hemisphere ice sheets, and equally rapid resumptions, suggested to be tied to a more gradual warming around Antarctica. At the beginning of the Last Interglacial, reconstructions indicate Arctic warming, a sea level rise of 2-5 meters, and a retreat of the Greenland ice sheet to only a small cap of ice around and north of the summit. There are a number of time periods in the past where sufficient proxy data is available to compare and understand the response of climate models. CCSM will be used to understand the role of glacial, deglacial, and interglacial initial conditions in the thermohaline response and recovery, and the coupling and teleconnections associated with oceanic, atmospheric, and sea ice processes. A transient CCSM simulation for the mid-Holocene (8000 to 3000 years ago) will evaluate the model's to explain key climatic transitions including the observed onset of the “modern” ENSO regime and the drying of the Sahara, when the smoothly varying Milankovitch solar cycle is imposed. As an understanding of abrupt climate change involves ocean, sea ice, ice sheet, and atmospheric feedbacks, a coordinated effort across CGD is necessary to address this issue.

c. Future Climate

There are many important questions about how the Earth's climate will evolve in the future: How will the surface atmospheric temperatures change and how much will sea level rise due to uptake of heat by the oceans? Will polar amplification mean that the Arctic temperatures rise more quickly, with a consequent large decrease in the Arctic sea ice? Will the stronger hydrological cycle in a warmer world manifest itself as more gentle precipitation or stronger floods and droughts? Will there be a slowdown of the North Atlantic thermohaline circulation? Will there be changes to the ENSO cycle, hurricane frequency, etc.?

The only systematic way to address these and other equally important questions is through climate models, such as the CCSM. The CCSM will be run with different scenarios of time-evolving combinations of forcings into the 21st and 22nd centuries to provide a range of responses to those scenarios. Thus CGD will be able to provide a range of responses across different scenarios for future climate with a single model. These results will then be compared to those from other models by involvement in the IPCC process, in order to help define a range of uncertainty for responses across different models. All of these uncertainty measures related to model responses are crucial to quantifying and reducing the various sources of uncertainty. This will provide more definitive estimates of possible future climate changes of interest to the impacts community and policymakers.

4. Development of an Earth System Model Hierarchy

4.1 Beyond a physical climate system model

Several of the most pressing scientific questions regarding the climate system and its response to natural and anthropogenic forcings cannot be readily addressed with traditional models of the physical climate. One of the open issues for near-term climate change, for example, is the response of terrestrial ecosystems to increased concentrations of carbon dioxide. Will plants begin releasing carbon dioxide to the atmosphere in a warmer climate, thereby acting as a positive feedback, or will vegetation absorb more carbon dioxide and hence decelerate global warming? Related issues include the interactions among land use change, deforestation by biomass burning, emission of greenhouse gases and aerosols, weathering of rocks, carbon in soils, and marine biogeochemistry. Exploration of these questions will require a more comprehensive treatment of the integrative Earth system. In order to address these emerging issues, physical models need to be extended to include the interactions of climate with biogeochemistry, atmospheric chemistry, ecosystems, and anthropogenic environmental change.

While the ultimate goal is a comprehensive Earth System Model (ESM), the CCSM project will work towards developing a first generation coupled chemistry-climate model in the next two to three years. A project of this scope will necessarily involve scientific partnerships across ESSL, NCAR and the external CCSM community. This model could be used to study the complex interactions among biota, chemical processes, and physical climate for paleoclimate studies or scenarios for future climate change. It could also be used to study variations of the chemistry of the present-day atmosphere driven by external forcing from solar variability and major internal natural modes of variability, such as ENSO.

The scientific questions to be addressed with this system include:

• What are the carbon/climate feedbacks?

• How do biogeochemical cycles of nitrogen, iron, and sulfur influence carbon/climate feedbacks?

• How do reactive chemistry and aerosols change in response to biogeochemistry processes, clouds, and climate?

• How do land use, land cover change, and water use modify biogeochemical processes?

• How do the hydrological and biogeochemical cycles interact?

• How do solar variations influence the chemistry and dynamics of the upper atmosphere, and how are these effects manifested in the lower atmosphere?

• How will future emissions and perhaps emission controls feedback onto climate?

• How will global climate change alter the structure and functioning of ecosystems, and in turn how will the feedbacks between the climate system and ecosystems change?

Many of the components of the coupled chemistry-climate model are under active development. The CCSM Biogeochemistry Working Group has developed comprehensive models of the terrestrial and oceanic carbon cycle and these components are now being ported to the latest versions of CCSM. Efforts are underway to create a comprehensive ocean ecosystem model and a terrestrial carbon-nitrogen cycle model. The ocean ecosystem module includes multiple phytoplankton functional groups, limitations by several major nutrients, nitrogen fixation, and treatments of sinking and remineralization of biological material. The terrestrial module can simulate multiple agricultural plant types and human-mediated disturbance of the land surface. Both of these modules are now being tested to understand their equilibrium behavior.

The coupled chemistry climate model will treat the interaction of aerosols with clouds, radiation, and ocean ecosystems. Prognostic treatments have been developed by CGD and ACD for the major aerosol species, including sulfate, nitrate, sea salt, soil dust, and black and organic carbonaceous species. New developments in the land model will include the changes in soil dust aerosols from disturbance of soils and modifications in land use by human populations. In the near future, the model will be able to predict both the mass and size distribution of major aerosols to better represent the microphysical evolution of aerosols, and will also treat the effects of aerosols on photochemistry. With these capabilities, the coupled chemistry-climate model could simulate the interactions of aerosols with both hydrological and biogeochemical cycles. These interactions have emerged as one of the more important uncertainties in human-induced climate change.

CGD, HAO, and ACD have added a detailed model of the stratosphere, mesosphere, and lower thermosphere to CCSM called the Whole Atmosphere Community Climate Model (WACCM). This model is capable of simulating the ozone distribution, the Brewer-Dobson circulation, tropical water-vapor, and other important features of the upper atmosphere. In essence, the MOZART chemical transport model developed by ACD has been merged with the CCSM atmosphere component. A parallel effort for the troposphere is yielding promising comparisons against measured vertical profiles of ozone, methane, and other radiatively active species. Once these two efforts are combined, CCSM will be able to simulate many important chemical processes from the surface through the lower thermosphere.

Another module that is needed for an Earth System Model is a land ice component. This is needed for transient climate studies over long time scales. Changes in glaciers and other land ice affect the radiative balance by changing the albedo, and they also affect the ocean by locally changing the freshwater input and salinity. This might affect the ocean circulation, especially the THC if there is significant melting of the Greenland ice sheet.

The industrial age and growing human population has produced large changes in land surface characteristics. Throughout the extratropics and tropics, there have been large decreases in natural vegetation, which has been converted to cities or to agriculture. Tropical deforestation is a particularly important aspect of this land use change, but extratropical land use, particularly reforestation, may also be important. Land use practices have also been implicated in the desertification of the Sahel region of Africa. The development of an Earth System Model must include these human influences on climate. CGD scientists are working with ISSE scientists to develop credible scenarios of future projected land use and land cover change driven by socioeconomic factors.

4.2 A hierarchy of models

The complexity of Earth's climate system will require a hierarchical modeling strategy that will aid in the development and understanding of the processes that maintain and regulate climate. The modeling hierarchy should ideally provide the ability to flexibly deal with phenomena across a wide range of scales of motion, and for different levels of complexity. The hierarchy of modeling tools should range from process models that incorporate the most complete detailed scientific understanding of important climate processes, through models of intermediate complexity that elucidate a theoretical understanding of the most important mechanisms operating in the climate system, to comprehensive global models of the climate system including physical, chemical, biogeochemical, vegetation, biological, and ecosystem capabilities. The need to understand and improve the treatment of processes operating on fine scales of motion represents an opportunity to leverage scientific work in areas like Large-Eddy-Simulation (LES) and Resolved Convection Modeling (RCM). In more general terms, climate studies on regional space scales will require that the global modeling framework will need to provide the capability to treat non-hydrostatic motion scales by, for instance, embedding regional models. CGD and MMM will work closely together to establish the significance of scale interactions in climate simulations. Moreover, CGD will also investigate the utility of methods for local or adaptive mesh refinement. Flexibility in the modeling framework should also provide for the hierarchical treatment of the core physical climate system with increasing levels of complexity that include chemical, biogeochemical, and other modeling capabilities, as well as connections to extensions like population and disease models and space weather. Another important attribute of the ESM hierarchy will be the ability to readily exploit observational opportunities (e.g., NASA's A-Train; field campaigns). In this regard, data assimilation capabilities will be an important component of an ESM modeling framework.

This hierarchical modeling environment will require a high-performance, flexible software infrastructure to allow for increased ease of use, performance portability, interoperability, and reuse of various modeling applications. The Earth System Modeling Framework (ESMF) will provide in the future such a capability by defining architecture for creating multi-component applications along with data structures and utilities for developing the components of a modeling hierarchy.

5. Vigorous scientific visitor program

The intellectual breadth required to develop an Earth System Modeling hierarchy will necessitate creative collaboration mechanisms to leverage scientific contributions from throughout the NCAR program as well as from external university partners. A priority must be placed on reinvigorating the CGD scientific visitor program through which long-term scientific interactions with university and national laboratory collaborators can be nurtured and maintained. A goal of the visitor program should be to provide the opportunity for long-term scientific visits, along with investment in local infrastructure support to ensure collaborators can make the most productive use of their time. Strategic partnerships with other NCAR divisions should also be a high priority, employing mechanisms to better facilitate long-term collaborative visits. Enhanced interactions with the university community will also allow CGD to play a more direct role in the education and training of the next generation of students.

6. Facility support to the community

CGD, through ESSL and NCAR and in collaboration with its partners in universities and government laboratories, serves the broad community through the development and ongoing support of numerical models that simulate the integrative Earth system, through the provision of climate-related data sets, and through efforts to develop and improve data processing software that address the evolving and diverse needs of the modeling and observational communities. The continued development of these community models, data sets and software is an integral part of our strategic plan for the future.

6.1 Community models

From the beginning, the CCSM (http://www.ccsm.ucar.edu/) has involved a significant part of the climate community in its development and application. There is community governance of all its activities. The governance of the scientific direction of the CCSM activities, for instance, occurs through a scientific steering committee (SSC), and half of the SSC members are from institutions outside of NCAR. Model development takes place at NCAR and at many collaborating institutions, and data from major experiments are shared with all users and analyzed at a variety of institutions. Improvements to the model are being made in collaboration with several national laboratories. Future directions are discussed and decided in a community process. An annual CCSM workshop allows hundreds of scientists to gather, discuss their work, and plan future activities. Ten model working groups meet during the year to discuss progress on model development and future plans. All model components and major model data sets are made available on the Web. Collaborators are allocated computer time through a community-based governance process, and CGD supports several liaison personnel to facilitate interactions with these scientists. The success of the CCSM can, in part, be attributed to the contributions from these outside collaborators. Several of the components of the model were developed collaboratively with other institutions. CCSM will continue to be used as a facility by scientists from across the United States and around the world.

WACCM (http://waccm.acd.ucar.edu/) is a next step in the evolution of Earth system models at NCAR. The development of WACCM is an interdivisional collaboration that brings together upper-atmospheric modeling in HAO and middle-atmospheric modeling in ACD with tropospheric modeling in CGD, using the CCSM as a common numerical framework. A comprehensive numerical model that spans from the Earth's surface to the thermosphere, WACCM reflects the importance of coupling between atmospheric regions and the necessity of studying dynamical and chemical processes in an interactive and comprehensive framework. WACCM is envisaged as a flexible model environment whose domain and component modules can be configured according to the specific problem under study.

The component models of CCSM and other, less complex models -- such as MATCH (a Model of Atmospheric Transport and Chemistry), SCAM (the CCSM CAM Single Column Model), and MAGICC/SCENGEN (Model for the Assessment of Greenhouse-gas Induced Climate Change/ A Regional Climate SCENario GENerator) are available to the community as well.

6.2 Community data sets

In response to community requests for easier access to climate model data, data products from the CCSM are available on-line (http://www.ccsm.ucar.edu/experiments/), including the ESG (https://www.earthsystemgrid.org/) and through the Geographic Information Systems (GIS) NCAR initiative (http://www.gis.ucar.edu/). These products, which are considerably more refined than the raw history data output directly from the CCSM, have proven to be very popular with climate change researchers, both in the United States and internationally.

In addition, an ongoing thrust within CGD has been the acquisition, evaluation, improvement, and restructuring of datasets, development of climatologies and high-level derived products, and facilitation of access to data and documentation in catalogs available through the Internet (http://www.cgd.ucar.edu/cas/dcats.html). New SST datasets and many new derived products from atmospheric reanalyses are especially prominent.

Observational datasets are available on a variety of grids and data formats: GRIB, netCDF, HDF4, HDF-EOS4 and binary. These datasets form the foundation for scientific studies and evaluating climate models. As noted in Section 3, data from satellites (e.g., Earth Observing System) need to be exploited in order to achieve our scientific objectives. These satellite datasets and the derived products will be available only in the HDF5 and HDF-EOS5 formats. The HDF5 formats are not extensions to HDF4. They can represent elaborate data structures and, as a result, are very complicated to use. CGD, in collaboration with SCD, will develop interfaces that facilitate use of the new satellite data.

The observational and CCSM data sets are also available through SCD's Community Data Portal (CDP: see https://cdp.ucar.edu/). The CDP is a collection of earth science datasets from NCAR, UCAR, UOP, and participating organizations.

6.3 Community software

Software tools to increase access to and display of data have been developed, and a substantial service activity within CGD has been devoted to outreach and teaching of data processing software, in particular the NCAR Command Language (NCL). NCL is the primary tool used to create the Community Data Sets previously described, and so it can readily access these data and transform them to common grid resolutions. NCL provides scientists with a robust, supported software tool for file handling, computations, and high quality graphics. An overarching goal of the NCL developers within SCD and collaborating members of CGD is to ensure that NCL can address the evolving and diverse needs of the modeling and observational communities. Some examples include:

• functions which use spherical harmonics to enable highly accurate regridding and derivations from basic quantities;

• interpolation functions including from hybrid coordinates to pressure coordinates; and

• special graphical templates that facilitate the creation of figures with consistent style.

An e-knowledge portal for file handling, data processing, visualization and tutorial support will continue to be developed (http://www.cgd.ucar.edu/csm/support/). This portal contains three levels of knowledge content: context-sensitive assistance, structured training, and user community information. CGD will continue to provide expert advice on using NCL to read, process and visualize data.

7. Infrastructure and resource requirements

Research progress on the many scientific topics discussed in this strategic plan will continue to require large amounts of high-performance computer time, associated data storage capabilities, and appropriately balanced high-speed communications networks. The recent IPCC exercise provides a basis for estimating the need for at least a 30-fold increase in high-performance computing resources within the next five years. Similarly, petabyte mass storage capabilities will be required to facilitate the research. Managing and sharing these resources with our collaborators will represent a major technical challenge, where we will work closely with our colleagues in the Computer Information and Systems Laboratory (CISL) to efficiently exploit available and emergent technologies. We recognize that these collaborative efforts will require computational infrastructure investments within CGD, such as enhancing data management capabilities within the division, which will be an integrated part of the division budget planning process.

Historically, there has been a strong collaborative component to the CGD program with scientists in the university and national laboratory communities. We believe the importance of these collaborations will continue to grow as the scope and complexity of the science expands. Therefore, we will plan to add to the scientific staff in targeted areas that will allow the program to fulfill its strategic goals through partnerships with external collaborators. To further facilitate external interactions, we will grow the visitor program to allow for the kind of long-term visits that will be required to allow external collaborators the opportunity to become more fully integrated in the CGD scientific program. We remain committed to community support and education through the sponsorship of regular workshops, such as the annual CCSM Workshop, along with tutorial workshops for graduate students and post-doctoral students that instruct participants on the use of modeling tools and available datasets. We will also continue to contribute to the organization and implementation of Advanced Study Program (ASP) Summer Colloquia on relevant scientific topics, in partnership with the ASP Director. Finally, CGD scientists will continue to serve as mentors for graduate students and post-doctoral fellows.