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The MIT Integrated Global System Model (IGSM)

IGSM components: Anthropogenic Emissions | Climate and Chemistry | Terrestrial Ecosystems & Natural Emissions

The MIT Integrated Global System Model (IGSM) is designed for simulating the global environmental changes that may arise as a result of anthropogenic causes, the uncertainties associated with the projected changes, and the effect of proposed policies on such changes. As described in numerous publications, the IGSM is a comprehensive research tool that is applied to questions regarding potential anthropogenic global climate change and its social and environmental consequences. The current IGSM formulation includes an economic model for analysis of greenhouse and aerosol precursor gas emissions and mitigation proposals, a coupled model of atmospheric chemistry and climate, and models of terrestrial ecosystems. All of these models are global but with appropriate levels of regional detail.

The schematic depicts the current framework and processes of the MIT Integrated Global System Model Version 2 (IGSM2). Solid lines between model components indicate exchanges represented in standard runs of the system; dash-dotted lines indicate model connections that exist and have been utilized in targeted studies; dotted lines indicate areas where implementation of feedbacks is under development.

In the integrated model, the combined anthropogenic and natural emissions model outputs are driving forces for the coupled atmospheric chemistry and climate model. the essential components of which are chemistry, atmospheric circulation, and ocean circulation. The climate model outputs drive a terrestrial ecosystems model predicting land vegetation changes, land CO2 fluxes, and soil composition, which feed back to the coupled chemistry/climate, and natural emissions models.

The economics model computes predictions of anthropogenic emissions of the key gases and aerosols generated from the world's economies and energy usage, and converts them into distributions by latitude where needed. Special provision is made for analysis of uncertainty in key influences, such as the growth of population and economic activity, and the pace and direction of technical change. The model also supports analysis of emissions control policies, providing estimates of the magnitude and distribution among nations of the costs, and clarifying the ways that changes are mediated through international trade. The model also supports examination of potential feedbacks of climate change onto predicted emission rates.

To calculate atmospheric composition, the model of atmospheric chemistry includes analysis of the climate-relevant reactive gases and aerosols at urban scales, coupled to a model of the processing of exported pollutants from urban areas (plus the emissions from non-urban areas) at the regional to global scale. Using a reduced-form urban airshed model derived from a detailed 3D model, atmospheric composition is thus resolved separately for polluted conditions (emissions in urban airsheds), and background conditions. Urban conditions, and pollutant properties important to human health, are resolved at low, medium and high levels of pollution depending on population density, local topography, and other factors.

The climate component of the IGSM currently includes a simplified, two-dimensional (2D) land- and ocean-resolving (LO) model of the atmosphere, coupled to a 3D ocean general circulation model (GCM). A submodel of atmospheric chemistry is incorporated to include the coupling between chemistry and climate (through greenhouse gases and aerosols), and between climate and chemistry (through temperature, humidity, cloudiness, rainfall, and surface fluxes). Together, the interacting components provide predictions of climate and air composition over both land and ocean as a function of latitude. In addition, the IGSM includes mass-balance models of the Greenland and Antarctic ice sheets. A mass balance model of the world's mountain glaciers is under development. These, when combined with the calculation of the thermal expansion of sea-water already included in the ocean models, will make it possible to simulate changes in sea-level.

The terrestrial ecosystems model component, developed by the Marine Biological Laboratory, is used to predict global ecosystem states, and supports the investigation of feedbacks in the climate system. It also provides a crucial step to studies of the impact of climate on natural ecosystems and agriculture. A natural emissions model component is used to simulate the natural emissions from the terrestrial biosphere to the atmosphere.

The linked IGSM components provide an emissions/chemistry/climate framework that is applied to questions relevant to policy-making. For example, predictions of greenhouse gas emission levels can be linked to uncertainties in future influences such as population growth and economic performance. Further, the effect of various emissions control policies on climate can be pursued, allowing analysis of the sensitivity of policy-relevant outcomes to critical assumptions in all the various components.

• Integrated Global System Model (IGSM) Version 2: Model Description and Baseline Evaluation MIT JOINT PROGRAM REPORT 124 Sokolov et al., 2005. [PDF: 1.1 MB]

• Integrated Global System Model for Climate Policy Assessment: Feedbacks and Sensitivity Studies CLIMATIC CHANGE 41(3/4): 469-546 Prinn et al., 1999. [PDF: 880 kB]. This article provides a description of the MIT IGSM as of 1998. Many changes since then are documented in MIT Joint Program Report 124 (above).

• Climate Dynamics, Atmospheric & Oceanic Chemistry and Circulations, and Ice

• Terrestrial Ecosystems and Natural Fluxes

• Economic and Policy Analysis and Anthropogenic Emissions

• Uncertainty Studies, and Detection and Attribution