The scale of environmental impacts associated with the manufacture of microchips is characterized through analysis of material and energy inputs into processes in the production chain. The total weight of secondary fossil fuel and chemical inputs to produce and use a single 2-gram 32MB DRAM chip are estimated at 1600 g and 72 g, respectively. Use of water and elemental gases (mainly N2) in the fabrication stage are 32,000 and 700 g per chip, respectively. The production chain yielding silicon wafers from quartz uses 160 times the energy required for typical silicon, indicating that purification to semiconductor grade materials is energy intensive. Due to its extremely low-entropy, organized structure, the materials intensity of a microchip is orders of magnitude higher than that of "traditional" goods. Future analysis of semiconductor and other low entropy high-tech goods needs to include the use of secondary materials, especially for purification.

The total energy and fossil fuels used in producing a desktop computer with 17-in. CRT monitor are estimated at 6400 megajoules (MJ) and 260 kg, respectively. This indicates that computer manufacturing is energy intensive: the ratio of fossil fuel use to product weight is 11, an order of magnitude larger than the factor of 1-2 for many other manufactured goods. This high energy intensity of manufacturing, combined with rapid turnover in computers, results in an annual life cycle energy burden that is surprisingly high: about 2600 MJ per year, 1.3 times that of a refrigerator. In contrast with many home appliances, life cycle energy use of a computer is dominated by production (81%) as opposed to operation (19%). Extension of usable lifespan (e.g. by reselling or upgrading) is thus a promising approach to mitigating energy impacts as well as other environmental burdens associated with manufacturing and disposal.

Reverse supply chains for the reuse, recycling, and disposal of goods are globalizing. This article critically reviews the environmental, economic, and social issues associated with international reuse and recycling of personal computers. Computers and other e-waste are often exported for reuse and recycling abroad. On the environmental side, our analysis suggests that the risk of leaching of toxic materials in computers from well-managed sanitary landfills is very small. On the other hand, there is an increasing body of scientific evidence that the environmental impacts of informal recycling in developing countries are serious. On the basis of existing evidence informal recycling is the most pressing environmental issue associated with e-waste. Socially, used markets abroad improve access to information technology by making low-priced computers available. Economically, the reuse and recycling sector provides employment. Existing policies efforts to manage e-waste focus on mandating domestic recycling systems and reducing toxic content of processes. We argue that existing policy directions will mitigate but not solve the problem of the environmental impacts of informal recycling. There are many opportunities yet to be explored to develop policies and technologies for reuse/recycling systems which are environmentally safe, encourage reuse of computers, and provide jobs.

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Life cycle assessment (LCA) is increasingly being used to inform decisions related to environmental technologies and polices, such as carbon footprinting and labeling, national emission inventories, and appliance standards. However, LCA studies of the same product or service often yield very different results, affecting the perception of LCA as a reliable decision tool. This does not imply that LCA is intrinsically unreliable; we argue instead that future development of LCA requires that much more attention be paid to assessing and managing uncertainties. In this article we review past efforts to manage uncertainty and propose a hybrid approach combining process and economic input-output (I-O) approaches to uncertainty analysis of life cycle inventories (LCI). Different categories of uncertainty are sometimes not tractable to analysis within a given model framework but can be estimated from another perspective. For instance, cutoff or truncation error induced by some processes not being included in a bottom-up process model can be estimated via a top-down approach such as the economic I-O model. A categorization of uncertainty types is presented (data, cutoff, aggregation, temporal, geographic) with a quantitative discussion of methods for evaluation, particularly for assessing temporal uncertainty. A long-term vision for LCI is proposed in which hybrid methods are employed to quantitatively estimate different uncertainty types, which are then reduced through an iterative refinement of the hybrid LCI method.

The digital revolution affects the environment on several levels. Most directly, information and communications technology (ICT) has environmental impacts through the manufacturing, operation and disposal of devices and network equipment, but it also provides ways to mitigate energy use, for example through smart buildings and teleworking. At a broader system level, ICTs influence economic growth and bring about technological and societal change. Managing the direct impacts of ICTs is more complex than just producing efficient devices, owing to the energetically expensive manufacturing process, and the increasing proliferation of devices needs to be taken into account.

Electronic waste (e-waste) has emerged as a new policy priority around the world. Motivations to address e-waste include rapidly growing waste streams, concern over the environmental fate of heavy metals and other substances in e-waste, and impacts of informal recycling in developing countries. Policy responses to global e-waste focus on banning international trade in end-of-life electronics, the premise being that e-waste is mainly generated in the developed world and then exported to the developing world. Sales of electronics have, however, been growing rapidly in developing nations, raising the question of whether informal recycling in developing countries driven by international trade or domestic generation. This paper addresses this question by forecasting the global generation of obsolete personal computers (PCs) using the logistic model and material flow analysis. Results show that the volume of obsolete PCs generated in developing regions will exceed that of developed regions by 2016-2018. By 2030, the obsolete PCs from developing regions will reach 400-700 million units, far more than from developed regions at 200-300 million units. Future policies to mitigate the impacts of informal recycling should address the domestic situation in developing countries.

Product lifespan is a fundamental variable in understanding the environmental impacts associated with the life cycle of products. Existing life cycle and materials flow studies of products, almost without exception, consider lifespan to be constant over time. To determine the validity of this assumption, this study provides an empirical documentation of the long-term evolution of personal computer lifespan, using a major U.S. university as a case study. Results indicate that over the period 1985-2000, computer lifespan (purchase to "disposal") decreased steadily from a mean of 10.7 years in 1985 to 5.5 years in 2000. The distribution of lifespan also evolved, becoming narrower over time. Overall, however, lifespan distribution was broader than normally considered in life cycle assessments or materials flow forecasts of electronic waste management for policy. We argue that these results suggest that at least for computers, the assumption of constant lifespan is problematic and that it is important to work toward understanding the dynamics of use patterns. We modify an age-structured model of population dynamics from biology as a modeling approach to describe product life cycles. Lastly, the purchase share and generation of obsolete computers from the higher education sector is estimated using different scenarios for the dynamics of product lifespan.