Human Activity in an Earth System Hierarchy


Integrated Assessment Modeling links knowledge across a wide variety of disciplines, including both the natural and social sciences, in a quantitative framework that can inform decisions regarding response options for the climate change issue. Response options include those relevant to emissions mitigation and to adaptation to expected impacts. As a model-based area of applied research, it fits naturally within CGD and NCAR more broadly as a complement to larger-scale modeling efforts of the climate system. For example, IA models can both directly link to Earth System Models by providing inputs and/or using outputs and indirectly inform ESM efforts by prioritizing research directions and identifying interesting scenarios to explore.

The newly-established integrated assessment modeling group was moved to CGD in FY10 and hired two new staff -- a demographer and an economist. The group, along with outside collaborators, has created and begun to use an initial version of an NCAR IA model, the Integrated-Population-Economy-Technology-Science (iPETS) model. This framework currently consists of three components: a global demographic model for projecting future population, urbanization, and living arrangements; a global, 9-region economic model that simulates changes in production, consumption, energy use, and greenhouse gas emissions; and a simple greenhouse gas cycle and climate model for projecting future atmospheric concentrations and changes in global average temperature.

Research in the IAM group involves development and use of the iPETS model, as well as collaborations with other research groups in the community, in order to explore three main topics: the influence of alternative socio-economic development paths on future greenhouse gas emissions and climate changes, better connecting long-term climate policy goals to shorter-term actions, and improving the treatment of uncertainty in integrated assessments. Over time the group aims to carry out research on the role of land use in responding to the climate change issue, to explore linkages between integrated assessment models and earth system models such as CCSM, and to improve the modeling of impacts and adaptation.

Recent Accomplishments


The effect of slower population growth on global CO2 emissions as estimated with the iPETS model. From O’Neill et al., 2010, PNAS. [high resolution image]

In 2010 the first set of global emissions scenarios developed with the iPETS model were completed and published in the Proceedings of the National Academy of Sciences. This analysis found that demographic change, including changes in population size, urbanization level, and aging, can significantly affect global emissions from energy use. In particular, it concluded that slower population growth could contribute significantly to emissions reductions necessary to avoid dangerous climate impacts, and that urbanization and aging can substantially affect projected emissions growth in particular world regions, especially Asia.

In addition, substantial model development took place in several aspects of the iPETS framework. For example, assessment of data sources and methodological options was completed to lay the groundwork for incorporating land use change into the iPETS framework, an essential step to facilitate future linking of the model to CESM to explore the effect of land use change on climate outcomes. Also, substantial effort was invested in the demographic module of iPETS with the aim of developing the capacity to generate global population and urbanization projections for our own use and for the use of the IAM community. In parallel, we are developing methods for generating spatially explicit population scenarios at the regional and global level.

Along with development and application of the iPETS model, the IAM group participated in collaborative work with other research groups, including an assessment of the feasibility of attaining various long-term climate policy targets such as the goal of limiting the increase of global average surface temperature to below 2 degrees C. This work demonstrated the importance of achieving emissions targets in 2050 that would keep such long-term options open, and concluded that some of the targets for 2050 currently discussed in international policy debates may be more stringent than necessary.

2011 and Beyond

In 2011 IAM research will focus on two key priorities. First, initial work on the implications of alternative development pathways will be expanded by examining in more detail both the potential for rapid urbanization, particularly in Asia, as well as the implications of these trends for emissions from energy use and for well being at the household level. This analysis is taking place in the context of a community-wide model comparison projection, the Asia Modeling Exercise, in which the NCAR IAM group is taking place. It will involve expanding the capacity of both the demographic module and the energy system in iPETS, in particular to generate not just aggregate outcomes such as national emissions levels, but also outcomes for particular household groups, such as the level of energy use by low-income rural households.

Second, the groundwork completed on incorporation of land use into iPETS will be built on to develop a first set of scenarios exploring the implications of global land use patterns for future emissions. This work will facilitate exploration of linking iPETS to land surface models such as CLM, a first step toward linking to earth system models such as CESM. In parallel we will continue to pursue other means of linking IAM work to earth system modeling, for example through a collaborative project to develop reduced form emulators of regional climate outcomes in CCSM. Emulators could then be used as a more computationally efficient means of representing climate system outcomes within an integrated assessment modeling framework.

At the same time, progress will be made on further developing the iPETS modeling framework, and making it available to the community to run, modify, or expand. This process will involve completion of a demographic projection tool that can be made publicly accessible, as well as refinement of the code for the economic model.