IGSM schematicAt the heart of the Joint Program's work lies the MIT Integrated Global System Modeling framework (IGSM). This comprehensive tool analyzes interactions among humans and the climate system. It is used to study causes of global climate change and potential social and environmental consequences.

Our central research efforts are organized around the IGSM and strive to improve the integration of climate science, technological change, economics, and social policy analysis into forecasts of the pressing issues in global change science and climate policy.

The MIT IGSM seeks to answer such questions as:

  • How effective and costly would specific policy measures be in alleviating climate change?
  • What are the advantages and risks of waiting for better scientific understanding of such change?
  • How will the oceanic and terrestrial uptake of carbon dioxide and other greenhouse gases be affected by changing climate?
  • What nations, regions, and economic sectors are most likely to be affected?

The IGSM consists of three primary components:

  1. Economics, emissions, and policy cost model for analysis of human activity as it interacts with climate processes, and to assess proposed policy measures;
  2. Climate and Earth system component: coupled dynamic and chemical atmosphere, ocean, land, and natural ecosystem interactions and feedbacks; and
  3. Land ecosystems and biogeochemical exchanges models, within a Global Land System framework, for analysis of the terrestrial biosphere.

These components then inform a component that analyzes the feedbacks and impacts of climate change. Within the current formulation of the IGSM the consideration of climate change impacts emphasizes terrestrial ecosystems and sea levels, feedbacks of changed climate onto the carbon cycle and natural emissions of CH4 and N2O, effects of climate change and ozone pollution on agriculture, and the interaction of climate chemistry with its counterparts in urban air pollution.

The configuration and capabilities of the IGSM are described in Sokolov et al., 2005 (Report 124). An earlier version is documented in Prinn et al. (1999).

An IGSM run data portal is available for public download for research purposes only. There is no user support. Click here to access it.

Economic Projection and Policy Analysis—The EPPA Model

The MIT Economic Projection and Policy Analysis (EPPA) model provides projections of world economic development and emissions along with analysis of proposed emissions control measures. It is used to analyze the processes that produce greenhouse-relevant emissions and to assess the consequences of policy proposals, providing estimates of the magnitude and distribution among nations of their costs and clarifying the ways that changes are mediated through international trade.

EPPA is a multi-sector, multi-region computable general equilibrium (CGE) model of the world economy. It utilizes the GTAP dataset (maintained at Purdue University), augmented by data on the emissions of greenhouse gases, aerosols and other relevant species, taxes, and details of selected economic sectors. Provision is made for analysis of uncertainty in key human influences, such as the growth of population and economic activity and the pace and direction of technical advance.

The model is formulated in two versions with contrasting representations of agent expectations. The recursive-dynamic (myopic) version is the more computationally efficient, allowing for an explicit treatment of capital stock turnover and greater regional and technology detail. The dynamic (forward looking) formulation provides the capability to examine questions where forward-looking behavior is particularly important.

The model projects economic variables (GDP, energy use, sectoral output, consumption, etc.) and emissions of greenhouse gases (CO2, CH4, N2O, HFCs, PFCs and SF6) and other air pollutants (CO, VOC, NOx, SO2, NH3, black carbon, and organic carbon) from combustion of carbon-based fuels, industrial processes, waste handling, and agricultural activities. Different versions of the model have also been formulated for targeted studies to provide consistent treatment of feedbacks of climate change on the economy, such as effects on agriculture, forestry, bio-fuels and ecosystems and interactions with urban air pollution and its health effects.

The standard EPPA model (version 4) is documented in Paltsev et al., 2005 (Report 125)
The forward-looking version is described in Gurgel et al., 2007 (Report 161).

A version of EPPA is now available for public download for educational and research purposes only. Click here for more information.

Climate Component - Earth System Model

The Earth system component of the IGSM has been constructed to be highly flexible, modular, and computationally efficient, so as to:

  • Run large ensembles of multi-century runs, varying uncertain climate model parameters as identified by our research;
  • Include different levels of model detail in components, as appropriate for specific studies.

The integrated model and components are as close as possible to state of the art while maintaining computational efficiency.

 We currently employ a hierarchy of Earth system representations within the IGSM. Our primary configurations are as follows:

  • IGSM2.2: includes a zonally-averaged model of atmospheric dynamics and chemistry, a thermodynamic sea-ice model, a land model with an ecosystem biogeochemistry model, and a mixed layer ocean model representing the processes of heat and carbon uptake. This configuration is our most computationally efficient Earth system model, and allows us to explore climate uncertainties by performing thousands of simulations.
  • IGSM2.3: as in the IGSM2.2, but with a three-dimensional (3D) model of ocean circulation, marine biology, and chemical processes that control the biogeochemical cycling of carbon, nutrients, and alkalinity. Despite the added complexity, this model is still relatively efficient, allowing on the order of hundreds of simulations on a Beowulf-class computer cluster.

In both of the configurations above, our Earth system component also includes an interactive atmospheric chemistry module, and an urban air chemistry component.

Utilizing this Earth system model of intermediate complexity facilitates the investigation of feedbacks and uncertainties between model components and with human drivers and mitigation goals. The simplified climate component enables extensive testing of these phenomena, which would not be practical in a calculation incorporating a high-resolution 3D chemistry/climate model. The Earth system model components of the IGSM2 are described in Sokolov et al., 2005 (Report 124).

In addition, we conduct supporting science to inform and improve the more computationally efficient IGSM. This work utilizes the following models:

  • A high-resolution 3D atmospheric general circulation and chemistry model based on the Community Atmospheric Model (CAM3) of the U.S. National Center for Atmospheric Research (NCAR).
  • A complex 3D marine ecosystem model that allows a self-assembling community structure (http://darwinproject.mit.edu).
  • A high-resolution 3D urban air-chemistry model to provide and test a simplified representation of urban processes in the IGSM.
  • The 3D ocean model that is used in the IGSM is continually being improved through our collaborations with scientists at the MIT Climate Modeling Initiative(CMI).
  • A 3D land system component that is developed by our collaborations with scientists at NCAR working with their Community Land Model (CLM) as well as at MBL with their advances in the Terrestrial Ecosystems Model (TEM).

The climate system component in the IGSM includes the following coupled submodels:

Terrestrial Ecosystems and the Global Land System Framework

Changes in land ecosystems due to changes in climate are important considerations in policy discussions. In addition, climate-driven changes in the terrestrial biosphere affect climate dynamics, through feedbacks on both the carbon cycle and the natural emissions of trace gases.

The terrestrial component of the IGSM includes dynamically linked hydrologic and ecologic models in a Global Land System framework, as depicted in the diagram below.

Hydrologic processes and surface-heat fluxes are represented by the Community Land Model (CLM), which is based on a multi-institutional collaboration of land models. Within the IGSM, CLM is dynamically linked to the global Terrestrial Ecosystems Model (TEM), developed by The Ecosystems Center at the Marine Biology Laboratory (MBL). Within the IGSM, TEM is used to simulate the carbon dynamics of terrestrial ecosystems. Methane and nitrogen exchange are considered through the Natural Emissions Model (NEM), which is driven by dynamic inputs from both TEM and CLM. The coupled CLM/TEM/NEM model system represents the geographical distribution of global land cover and plant diversity through a mosaic approach, in which all major land cover types and plant functional types are considered over a given domain, and are area-weighted to obtain aggregate fluxes and storages.

The Global Land System Framework is documented in Schlosser et al., 2007 (Report 147).


Terrestrial Ecosystems and the Global Land System Framework

The Joint Program’s Integrated Global System Modeling (IGSM) framework simulates the impact of changes in human and Earth systems, and interactions between these elements, on agricultural outcomes. For example, in the human systems component of the model, land-use change decisions are influenced by the demand for food and incentives for bioenergy. Earth system elements of the model resolve how changes in carbon and nitrogen cycles, CO2 fertilization, ozone damage, evapotranspiration and albedo effects impact yields.