Impacts of Demographic Events on US Household Change

Understanding the determinants and consequences of changes in household size and structure is important to a wide range of social, economic, and environmental issues. In the U.S., living arrangements have undergone tremendous changes over the past 200+ years, but have been relatively stable since 1980. What drove these changes, and whether the recent stability can be expected to continue, are critical questions. While research has identified demographic events that drive particular types of changes in households, a systematic understanding of past and potential future changes is lacking. We use a household projection model to assess the sensitivity of household size and structure to various demographic events, and show that outcomes are most sensitive to changes in fertility rates and union formation and dissolution rates. They are less sensitive to the timing of marriage and childbearing and to changes in life expectancy. We then construct a set of future scenarios designed to reflect a wide but plausible range of outcomes, including a new set of scenarios for union formation and dissolution rates based on past trends, experience in other countries, and current theory. We find that the percentage of people living in households headed by the elderly may climb from 11% in 2000 to 20-31% in 2050 and 20-39% in 2100, while the average size of households could plausibly be as low as 2.0 or as high as 3.1 by the second half of the century

Interpreting UN Urbanization Projections Using Multi-state Model

The United Nations provides the most comprehensive and widely used projections of urbanization at the national level, based on a method that projects differences in urban and rural growth rates over time. Taking the case of China as an illustration, we use a multi-state model to explore the implications of this projection for rural-urban migration, its plausibility, and the uncertainty associated with it. We find net that the UN urbanization projection implies a net rural-urban migration path of just over 10 million per year for the next 20 years, followed by a substantial decline over the 2020s. We also find that alternative migration scenarios can produce a wide range of outcomes for urbanization and for the age structures of rural and urban populations, suggesting that urbanization projections that reflect a full range of uncertainty are desirable. Given the range of possible outcomes for rural and urban age structures - some of which are unlikely or infeasible - it appears advisable that urbanization projections should explicitly model these populations and the age structure of migration

Learning from global emissions scenarios

Scenarios of global greenhouse gas emissions have played a key role in climate change analysis for over twenty years. Currently, several research communities are organizing to undertake a new round of scenario development in the lead-up to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). To help inform this process, we assess a number of past efforts to develop and learn from sets of global greenhouse gas emissions scenarios. We conclude that while emissions scenario exercises have likely had substantial benefits for participating modeling teams and produced insights from individual models, learning from the exercises taken as a whole has been more limited. Model comparison exercises have typically focused on the production of large numbers of scenarios while investing little in assessing the results or the production process, perhaps on the assumption that later assessment efforts could play this role. However, much of this assessment potential remains untapped. Efforts such as scenario-related chapters of IPCC reports have been most informative when they have gone to extra lengths to carry out more specific comparison exercises, but in general these assessments do not have the remit or resources to carry out the kind of detailed analysis of scenario results necessary for drawing the most useful conclusions. We recommend that scenario comparison exercises build-in time and resources for assessing scenario results in more detail at the time when they are produced, that these exercises focus on more specific questions to improve the prospects for learning, and that additional scenario assessments are carried out separately from production exercises. We also discuss the obstacles to better assessment that might exist, and how they might be overcome. Finally, we recommend that future work include much greater emphasis on understanding how scenarios are actually used, as a guide to improving scenario production

Projecting U.S. Household Changes with a New Household Model

Anticipating changes in number, size, and composition of households is an important element of many issues of social concern. To facilitate continued progress in these areas, an efficient household projection model with moderate data requirements, manageable complexity, explicit accounting for the effects of demographic events, and output that includes the most important household characteristics is needed. None of the existing modelling approaches meets all these needs. This study proposes a new type of headship rate model that projects changes in age- and size-specific headship rates by accounting for the effect of changes in population age structure, changes in the age structure of household heads, and the effect of demographic events. We compare model results to historical data on the last 100 years of experience in the United United States, and to results from a projection over the next 100 years using the dynamic household model ProFamy. Results show that the new model is a substantial improvement over the commonly used constant headship rate approach. A simplified version of the model that does not require projecting the effect of changes in demographic events on headship rates appears to produce reasonably accurate projections of the composition of the population by household size and age of the household head

The Accuracy of Past Projections of U.S. Energy Consumption

Energy forecasts play a role in the development of energy and environmental policy. Evaluations of the accuracy of past projections can provide insight into the uncertainty that may be associated with current forecasts. They can also be used to identify the sources of inaccuracies, and potentially lead to improvements in projections over time. Here we assess the accuracy of projections of U.S. energy consumption produced by the Energy Information Administration over the period 1982-2000. We find that energy consumption projections have tended to underestimate future consumption. Projections 10 - 13 years into the future have had an average error of about 4%, and about half that for shorter time horizons. These errors mask much larger, offsetting errors in the projection of gross domestic product (GDP) and energy intensity. GDP projections have consistently been too high, and energy intensity projections consistently too low, by more than 15% for projections of 10 years or more. Further work on the source of these sizable inaccuracies should be a high priority. Finally, we find no evidence of improvement in projections of consumption, GDP, or energy intensity since 1982

Household Projections for Rural and Urban Areas of Major Regions of the World

Demographic dynamics are important drivers of environmental change, including effects on climate through energy and land use that lead to emissions of greenhouse gases. These dynamics include changes to population size, age structure, and urbanization, as well as changes in household living arrangements. Population and household projections are therefore essential for investigating potential future demographic effects, but no long-term, global projections exist that simultaneously describe consistent outcomes for population, urbanization, and households. We therefore develop a new set of population/household projections for nine world regions. The projections are based partly on existing population and urbanization projections, partly on new multi-state projections for China and India, and on a new household projection using age-, size-, and urban/rural-specific headship rates. We discuss principle results that foresee future aging, urbanization, and trends toward smaller household sizes

Linking Mid-century Concentration Targets to Long-Term Climate Change Outcomes

We present a framework that could inform the choice of an interim (mid-21st century) target in the making of climate mitigation policy. The idea of interim targets for greenhouse gas concentration has been proposed previously as a way to bridge short- and long-term climate targets, address concerns about the rate of temperature change, and provide guidance in planning for energy infrastructure while scientific understanding improves and long-term climate goals are negotiated. Our analysis relates a wide range of mid-century equivalent CO2 (eCO2) concentrations to rates of temperature increase as well as total long-term temperature increases, accounts for uncertainties in the carbon cycle and the climate response (including climate sensitivity, ocean diffusivity, and aerosol forcing), and provides a rough measure of the economic feasibility of different emissions pathways. Our results show, for example, that for a roughly 50% likelihood of limiting long-term warming to 20C above the pre-industrial level, and with the constraint that global emissions should not have to be reduced by more than 2.5%/year, the mid-century concentration needs to remain below about 470 ppm eCO2 (including only the Kyoto gases and defined relative to a year 2000 baseline). For a roughly 83% likelihood of achieving the same temperature goal, the mid-century target needs to be about 440 ppm. These targets require that emissions between 2010 and 2050 average to approximately the current level and the 1990 level, respectively. Our framework illustrates how delay in emissions reductions in the near term forecloses options in the long term. Finally, we demonstrate how near-term reductions of CO2 from a particular source, deforestation, can significantly facilitate the achievement of long-term temperature goals

Accounting for Household Heterogeneity in General Equilibrium Models

The paper investigates differences in total consumption and demand according to how heterogeneity is incorporated into the model of the general equilibrium type. The sensitivity analysis for a static case with CES utilities and production functions demonstrates that the relative differences in total consumption can be considerable when a model with several heterogeneous consumer groups is compared to the one with a representative consumer. In a dynamic model, investment is proved to depend both on the production and consumption sides even in the case with one-sector production. By using the first-order optimality conditions to the multi-sector case it is shown that a model has enough capability to represent household heterogeneity to be applied for integrated assessment of carbon cycle emissions and energy demand

Production Data for the Population-Environment-Technology (PET) Model

This report describes the production data serving as an input to the Population-Environment-Technology (PET) model (Dalton and Goulder, 2001; Dalton et al., 2008). The PET model is a multi-sector, multi-region computable general equilibrium model of the global economy. We describe the procedures used to develop regional production data for the model. GTAP (Global Trade Analysis Project) represents the major production data source. The document explains the structure of the data and the modifications we make to it, including modifications to the treatment of trade, physical energy quantities, and household consumption