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Environ. Sci. Technol. 2011, 45, 182–188

Patterns of Iron Use in Societal Evolution§ ¨ L L E R , * ,†,‡ T A O W A N G , †,‡ DANIEL B. MU AND BENJAMIN DUVAL† Center for Industrial Ecology, School of Forestry and Environmental Studies, Yale University, 205 Prospect Street, New Haven, Connecticut 06511, United States and Department of Hydraulic and Environmental Engineering, Norwegian University of Science and Technology, S.P. Andersens veg 5, 7491 Trondheim, Norway

Received July 6, 2010. Revised manuscript received October 30, 2010. Accepted November 3, 2010.

A dynamic material flow model was used to analyze the patterns of iron stocks in use for six industrialized countries. The contemporary iron stock in the remaining countries was estimated assuming that they follow a similar pattern of iron stock per economic activity. Iron stocks have reached a plateau of about 8-12 tons per capita in the United States, France, and the United Kingdom, but not yet in Japan, Canada, and Australia. The global average iron stock was determined to be 2.7 tons per capita. An increase to a level of 10 tons over the next decades would deplete about the currently identified reserves. A subsequent saturation would open a long-term potential to dramatically shift resource use from primary to secondary sources. The observed saturation pattern implies that developing countries with rapidly growing stocks have a lower potential for recycling domestic scrap and hence for greenhouse gas emissions saving than industrialized countries, a fact that has not been addressed sufficiently in the climate change debate.

Introduction The massive growth of global material use over the past years, particularly due to the rise of emerging market economies, has revived questions about the long-term prospects and sustainability of resource use (1) and the possibilities to reduce energy use and to mitigate greenhouse gas emissions associated with their production (2, 3). The iron and steel industry, for example, accounts for about 6% of global final energy use and about 6-7% of global anthropogenic carbon dioxide emissions (2, 4). An effective way to reduce resource depletion, waste generation, energy use, and environmental impacts associated with resource use is to reuse products or components or to recycle scrap. Efforts to reduce these impacts in the medium- and long-term should therefore be informed by models that are capable of explaining and anticipating resource use and scrap availability. Traditional resource models and are often based on the Environmental Kuznets curve (EKC), which hypothesizes that the relationship between per-capita income and environ§ This manuscript is part of the Environmental Policy: Past, Present, and Future Special Issue. * Corresponding author address: Department of Hydraulic and Environmental Engineering, Norwegian University of Science and Technology, S.P. Andersens veg 5, 7491 Trondheim, Norway; phone: +47-73594754; fax: +47 73591298; e-mail: [email protected]. † Yale University. ‡ Norwegian University of Science and Technology.

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mental indicators has an inverted U-shape. Applied to resources, the hypothesis implies that the intensity of resource use (IU)sdefined as the ratio of physical material use per incomesgrows rapidly in initial stages of industrialization, but eventually falls as income rises further (5, 6). The declining IU is generally explained by structural change toward information-intensive industries and services that are assumed to be less material-intensive than the manufacturing sector, increasing environmental awareness, enforcement of environmental regulations, better technology, and higher environmental expenditures. The limitations of EKC-based resource models have been discussed widely (7-10) and include the following: (i) EKC models are based on statistical correlation, lacking a systems perspective capable of explaining the mechanisms that shape the IU and other important variables in resource cycles, such as scrap flows or mine production; (ii) they implicitly assume that resource cycles are driven by production (flow from process 7 to process 8 in Figure 1) and tend to neglect the stocks of different service-providing product categories; (iii) they lack robustness, because IU is an abstract ratio of two flow variables that tends to fluctuate, resulting in a weak foundation for estimating its future trend when used for scenario purposes. IU approaches are essentially based on observed patterns of specific flows or relationships between flows. We propose here an alternative based on patterns of in-use stock evolution. Observing stocks in use has several advantages: (i) stocks in use form the missing link of traditional models to explain the relationship between end use (flow into the stocks) and obsolete scrap generation (generated from products exiting in-use stocks); (ii) they have a physical meaning as they provide services to people and define their lifestyles; and (iii) they have a more robust behavior due to their inertia and are therefore better suited for long-term analyses. Iron is by far the most important metal used by man in terms of quantity and environmental impact (11). The trend in raw steel production over the past decades (Figure 2) shows two important phenomena: (i) industrialized countries experienced a similar patternsa strong growth, followed by a slack (with different distinctness) and stabilization on a high level; (ii) the current level of steel production per capita varies by a factor of 4-5 among the countries shown here (U.K. ca. 200 kg/a, Japan ca. 900 kg/a). In 1954, during the boom of American industrialization, geochemist Harrison Brown speculated that the iron stock incorporated in products in use might eventually reach saturation (12). His reasoning was that iron, unlike many other metals, is mainly used for bulk applications such as buildings, infrastructures, or transport vehicles, for which there is not an endless increase in demand. A recent study demonstrates that the per-capita iron stock in use in the U.S. indeed reached a plateau around 1980 (13). This observation led us to ask whether this apparent saturation is a transient phenomenon limited to the U.S., or whether it reveals a more fundamental pattern of iron use in the path of a country’s development. This implies the hypothesis that per-capita iron stocks in use indicate the level of industrialization: they are negligible in agrarian societies, they increase with industrialization, and they remain on constant, high levels during transitions from industrialized to information or service-based economies. Should this iron saturation hypothesis be supported by further research, patterns of iron stock evolution observed in industrialized countries could be used as benchmarks for 10.1021/es102273t

 2011 American Chemical Society

Published on Web 12/01/2010

FIGURE 1. System definition of the iron cycle used to determine the in-use stocks. Transformation processes designated in blue, market processes are shown in pink. using a top-down approach. Of interest is how the growth rate changes over time, whether these countries have reached saturation, and if they dohave what the potential saturation levels for different product categories are. Subsequently, the iron stocks in use are plotted against economic activity as an explanatory variable to develop crude first estimates of contemporary iron stocks in use for all countries and the globe.

Methods

FIGURE 2. Crude steel production in various countries, ca. 1900-2008: total production (top) and production per capita (bottom). ACFB ) sum of Australia, Canada, France, and the United Kingdom; 1 Mt/a ) 1 million metric tons per annum. emerging market economies and thereby provide a more solid basis to inform policies on long-term steel demand, scrap generation, and energy demand and emissions related to their production. Several studies have been conducted that assume stock saturation to estimate future obsolete scrap generation, e.g., for buildings (14-16), vehicles (17), aluminum (18), and steel (19), however, there is a lack of literature that analyzes the evidence for this assumption. In this paper, we first analyze the patterns of per-capita iron stocks in use over time for six industrialized countries

The historic iron stocks in use for Australia, Canada, France, Japan, the U.K., and the U.S. were calculated using a system definition described in Figure 1 and a dynamic material flow model described in ref 13 and the Supporting Information. Starting points were historical data for crude steel and castings production and information about the sectors to which the material was delivered. Historic trade statistics for about 200 product categories were used to account for imports and exports of iron embedded in semis, parts, and final products, and to compute the amount of iron entering use in different product categories. For each product category, assumptions about the product lifetime were made to calculate the amount of iron leaving use and the stock accumulation rate. Stock data are most sensitive to the parameters of the distribution of finished steel and castings among different manufacturing sectors, the import and export of iron embedded in parts and final products (“indirect iron trade”), and the lifetime of the final products. Lifetime data may vary among products within a product category, among countries, and over time while data sources are scarce (20). A sensitivity analysis was conducted to analyze the impact of different shapes of lifetime distribution functions (normal, log-normal, Weibull) and different average lifetimes (see Supporting Information). Results in the main paper are shown only for normal distribution with high, medium, and low estimates for the average lifetimes. Given the lack of country-specific lifetime data, the parameters were chosen to be identical for all countries to improve transparency and comparability. Medium lifetime assumptions are used in subsequent analysis for all countries with exception of Japan, where studies have indicated significantly shorter lifetimes for buildings (21, 22), and often shorter lifetimes for infrastructures, vehicles, and machinery are used (23). Therefore, short lifetime assumptions are subsequently assumed for Japan. VOL. 45, NO. 1, 2011 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 3. Per capita iron stocks in use versus per capita GDP PPP (1990 international dollars). Iron stock data are based on medium lifetime assumptions, except for Japan, where lower lifetime estimates were applied. The thick gray-green line is a fitted logistic growth curve used to estimate the contemporary iron stocks in other countries. The contemporary iron stocks in the remaining 222 countries were calculated based on the level of economic activity, assuming that these countries follow a similar pattern of iron stock per economic activity as observed in the six countries analyzed in more detail. Economic activity was measured in GDP based on purchasing power parity (PPP) in 1990 international dollars (24), because physical investments into capital stocks are thought to be better reflected by PPP, and because time series reaching long back in time are available. The average intensity of iron stock per economic activity (Figure 3) was derived by curve fitting assuming a logistic growth function with a predefined saturation of 10 t/cap and 0 t/cap for GDP below 1800 USD. See Supporting Information for a comparison with a Gompertz approach.

Results The simulation results (Figure 4) show that in 2005, the total per-capita iron stocks in industrialized countries varied between 8 (France and U.K.) and 12 t (Canada) (assuming shorter lifetimes for Japan), thus a much lower range than could have been expected from the wide range of per-capita steel production. The relative similarity in the employment of iron in various industrialized societies indicates that stocks behave more robustly than flows. The decomposition of the total iron stock indicates further similarities: all of the investigated countries employ most of the iron in Construction, followed by Machinery and Appliances, Transportation, and Others. Furthermore, the percapita iron stocks are fairly similar for Machinery and Appliances (from 2 tons in France to 3 tons in Canada), Transportation (from 1 ton in U.K. to 2 tons in U.S.), and Others (from 0.3 to 0.6). However, there are large differences in the amount of iron employed in Construction (from 2.5 tons in France to 9-10 tons in Japan). For all countries observed, the stock growth rate tends to be relatively small in early stages of industrialization. The peak in both growth speed and iron and steel demand is reached only after a level of about 2 tons per person has been passed. This might be explained by the fact that an initial capital stock of iron-intensive plants and infrastructures to produce, transport, and manufacture steel iron and steel into different products needs to be established prior to peak growth. A recent top-down study (25) and the subsequent estimation show that China has just reached this threshold level. 184

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The observed countries strongly differ in terms of their growth speed during industrialization: for example, to increase the iron stock from 2 to 7 t/cap, France needed about 60 years, while Japan achieved the same in about 20 years. Newly industrialized countries tend to built up their iron stocks faster than the front runners did, supposedly because the followers can benefit from the major inventions and innovations in iron and steel containing products and structures made earlier (for example railways, automobiles, construction technologies). The U.S., France, and the U.K. have reached a plateau in overall per-capita iron stocks. More importantly, saturation can be observed independent of the lifetime assumptions (bands in Figure 4). The levels of saturation, however, differ with the assumed lifetimes. The saturation levels for France and the U.K. (both about 8 t/cap for medium lifetime) are lower than that found for the U.S. (ca. 10-11 t/cap). Due to improvements in the indirect trade analysis, the saturation level for the U.S. identified here is slightly lower than that found previously (13). The U.K. reached saturation, like the U.S., at the end of the 1970s, whereas France had a delay of about one decade. Both economies use roughly the same amount of iron in Construction (ca. 4 t/cap), but the U.K. economy uses more iron in Machinery and Appliances, and France has larger iron stocks in Transportation and Others. Japan’s per-capita iron stock is still growing, although its growth rate has declined over the past two decades. This slowdown is more pronounced if shorter lifetimes are assumed. Given the current trend, Japan could reach saturation at about 12-13 t/cap within a decade or two. The per-capita stocks in Transportation, Machinery and Appliances, and Others have reached saturation. In contrast, the iron reservoir in Construction (9 tons for lower lifetimes) is about double that of other countries analyzed, and is still growing. Several factors might explain this. Due to the high population density, Japan tends to build higher and thus employs more steel-intensive construction technologies (concrete and steel) than less densely populated countries, which tend to use more wood or brick. It can be assumed that the steel-intensive construction technology more than compensates the smaller per-capita floor area. In addition, Japan’s high level of exposure to earthquakes, combined with its hot and humid and thus corrosive climatic conditions, has not only triggered higher building replacement rates (resulting in reduced lifetimes), but has also led to stricter design regulations for new buildings and seismic retrofit of existing vulnerable buildings (26), thereby further increasing the iron density of the building and infrastructure stock due to steel reinforcements. The finding of a declining growth rate confirms a recent study by Hirato et al. (27), however, the absolute values vary by about 30%, probably due to different assumptions for lifetimes and initial conditions. Australia’s and Canada’s per capita iron stocks, in contrast, show no signs of saturation. Construction stocks are relatively large (about 6 t/cap) but smaller than in Japan, and account for most of the total growth. The reason for their continued growth might be related to the fact that both countries have large mining sectors and experienced sharply growing exports of resources over the past years, which involved a growing steel reservoir in infrastructures for mining, processing, and transportation of ores materials. Figure 3 shows that iron stocks in use tend to start growing at per capita incomes of 1000 $ (U.S.) to 4800 $ (Australia), and they reach a plateausif at allsat per capita incomes between 13,000 $ (U.K.) and 18,000$ (U.S.). The late start in iron stock growth of the Australian economy can be explained by its large agricultural sector and by a likely underestimation of its iron stocks at the beginning of the 20th century, when domestic steel production was insignificant and steel imports in the form of metal or products were recorded poorly. As

FIGURE 4. Decomposition of total iron stocks (blue) into four product categories. A normal lifetime distribution function is applied to each category with various average product lifetime τ and standard deviation σ (in years). The uncertainty of the simulation is indicated as a band, with its upper bound, dark midline, and lower bound corresponding to the higher, medium, and lower lifetime assumptions. expected, Australia, Canada, and Japan have growing iron stocks at higher per capita incomes of 22-24,000 $. Global iron stocks in the ground (reserves) are estimated to be 79 Gt or 12 t/cap (28) (Figure 5 top). The largest iron stocks in reserves are found in Brazil (16 Gt), Russia (14 Gt), Ukraine (9 Gt), Australia (9 Gt), and China (7 Gt). In terms of per capita iron stocks in reserves, Australia (440 t/cap) leads before Sweden (240 t/cap), Kazakhstan (220 t/cap), and Ukraine (190 t/cap). Although China and India have

substantial iron reserves in absolute terms, their large population leads to small per capita reserves (China 5 t/cap and India 4 t/cap). In contrast, the global iron stocks in use have reached about 18 Gt or 2.7 t/cap, which is about 23% of the amount of the global reserves (Figure 5 bottom). The largest absolute in-use iron stocks are found in the U.S. (3.2 Gt), followed by China (2.2 Gt), Japan (1.7 Gt), Germany (0.7 Gt), and Russia (0.7 Gt). On a per-capita basis, Japan and Canada (12 t/cap) VOL. 45, NO. 1, 2011 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 5. Density-equalizing maps of the iron stocks in 2005 in ore reserves (top) and in use (bottom). Country sizes are distorted in proportion to their absolute iron stocks. Color scale indicates per capita iron stocks. lead in front of the U.S. (11 t/cap). Although China’s per capita iron stock (2.2 t/cap) is only about 20-25% that of industrialized countries, due to its large population, it constitutes the second largest iron stock in use. India, which has a similar population multiplier, has about five times smaller iron stocks (0.4 t/cap) than China. In comparison, Hatayama et al. (19) estimated the global in-use iron stock to be 12.7 Gt or about 2 t/cap, thus slightly less (probably due to differences in the lifetime assumptions). Primary iron resources tend to be strongly represented in the Southern hemisphere, while secondary iron resources are more concentrated in the Northern hemisphere. The largest exception is Africa, which neither disposes of large (identified) primary nor secondary iron resources. While South America seems to be well endowed with iron ore for its industrialization, Africa, the Middle East, and Asia are more likely to depend on imports over the coming decades.

Discussion The discovered patterns of iron stocks in use confirm and complement previous studies of IU patterns. The decreasing IU for steel observed for many industrialized countries (29) is in line with and could be explained by a tendency for per-capita iron stocks to flatten off at a certain point while GDP remains growing. Speculations about an absolute decoupling in steel demand, however, cannot be supported by this study: none of the analyzed countries shows a shrinking per-capita iron stock in use, which would be needed for long-term absolute decoupling of steel demand. Given the stock patterns observed, a more plausible scenario is 186

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that postindustrial societies still need to maintain and replace substantial iron stocks in use. Several industrialized countries, however, show clear signs of a flattening of their iron stocks at levels between 8 and 12 t/cap, which gives rise to an alternative hypothesis: that iron stocks in use grow during industrialization, but saturate in postindustrial societies. The saturation hypothesis is supported by the results found for the U.S., France, and the U.K., while Japan shows signs of a flattening of per-capita iron stocks during the past decade. However, Australia and Canada have still growing per-capita iron stocks. A more conclusive explanation of this behavior is not possible on the basis of the highly aggregated data currently available. However, it can be hypothesized that the continuing growth of iron stocks in Australia and Canada results from the heavy dependence of their economies on the mining sector. The strong growth in global minerals use over the past years has led to substantial investments in iron-intensive infrastructures and machinery for mining in these countries (for example railways and harbors for ore transport or water and electricity supply to remote mining sites). The growing per-capita iron stocks in Australia and Canada might therefore reflect a prolonged industrialization process due to their focus on exploiting resources for export to emerging market economies. Although the mining sector usually absorbs a relatively small fraction of the total steel production, it might be very large on a per-capita basis for countries with 2 orders of magnitude smaller population than China or India providing a large share of the giants’ resources. The hypothesis that per-capita iron stocks in use relate to the degree

of industrialization can therefore not be rejected on the basis of the Australian and Canadian results. The prospect of saturating iron stocks per person opens up alternative methods for forecasting iron and steel demand: patterns of iron stock development in industrialized countries can be used as benchmarks for emerging market economies. Models that integrate stocks and flows have several advantages compared to exclusively flow-based methods: (i) Inuse stocks reflect the ultimate demand for services more adequately, while flows are necessary means to build up and maintain service-providing stocks. (ii) Patterns of in-use stocks are more robust than flows, which makes them more robust for long-term forecasting, but also less accurate for short-term projections. (iii) Stock dynamics allows for a massbalance-consistent explanation for material demand as well as scrap generation from retiring products, which is not the case for purely flow-based approaches. (iv) Flows are poor indicators for saturation and its implications, because a constant input flow over a longer time period is possible not only for a saturation phase, but also for a growth phase, in which case there is no way of anticipating potential saturation levels or their timing. For example, the slack of iron and steel demand during the 1970s and 1980s coincides with a period in which several industrialized countries passed the inflection point in their iron stock growth to slowly approach saturation in the 1980s and 1990s. Saturation, or the passing of the inflection point, can therefore be used as an alternative explanation for the drop in steel demand in this period, a phenomenon that might repeat itself in China. The observed stock patterns demonstrate that the opportunities for recycling and therefore for reducing resource depletion and GHG emissions change dramatically during a country’s evolution. The potential for recycling domestic scrap is very low in emerging market economies where stocks are growing rapidly, while industrialized countries can benefit from stocks (and related investments in the form of energy use and emissions) built up earlier. Importing scrap cannot solve the problem because of the small potential compared to the emerging markets’ resource demand (e.g., the U.S. generates about 55 Mt/year of traded ferrous scrap (13), while China produced 570 Mt of steel in 2009). The concept of a circular economy remains an illusion for emerging market economies. In the long term, a saturation of iron stocks in use would open the opportunity to completely change the steel industry’s resource base. Assuming the global population and its iron stock in use stabilize, the amount of iron units exiting the use phase would be as large as the amount of iron units entering use. It is therefore possible to envision a system of iron and steel management that is entirely based on secondary resources, using the built environment as the key mine of the future. Such a scenario would not only avoid primary resource exploitation and mining wastes (tailings), but it would also significantly reduce energy consumption and greenhouse gas emissions in the iron and steel industry, mainly because the most energy- and CO2-intensive process, the blast furnace, could be avoided. The stock dynamics approach has therefore a large potential to improve the development of models and scenarios for energy and climate change. Although a significant absolute dematerialization seems unlikely for steel, it is not entirely unrealistic for iron ore. Whether such a vision becomes feasible depends on two key factors: the stock dynamics (including an economic scrap recovery from retiring stocks in use) and the technical challenges for recycling (e.g., scrap sorting and refining to achieve high-quality steels from scrap). Notwithstanding this vision, projections into the future need to be carried out with caution. The saturation patterns observed result from two overlapping factors: the demand

for service-providing stocks and their iron density. For example, demand for cars can increase, while iron density per car declines due to substitution of iron with aluminum, plastic, or high-strength steels in engine blocks and frames. The model applied here cannot decouple these two drivers. More refined models using a combination of top-down and bottom-up approaches are needed to analyze the relative impacts of product stock demand and evolving technology (15, 30). Caution needs to be exercised also with extrapolations of the findings for iron to other materials. Materials play different roles in the economy according to their specific properties, abundances, and prices. Patterns of stock evolution observed for iron are strongly linked with iron’s role in industrialization, which is not necessarily the case for other materials. Models of entire resource cycles are a first step not only to put economic analysis on a mass-balance-consistent basis (31), but also to include the use phase, which connects demand for resources with generation of secondary resources, and thereby allows for a consistent description of circular economies. This broadening of the system boundaries is essential to place long-term forecasts for primary and secondary resource use on a more robust basis and thereby provide improved guidance for industry and government policy on resource management, energy, pollution control, and international trade.

Acknowledgments We thank Nalin Srivastava and Leon Dijk for their support in data gathering, and Hans-Jo¨rn Weddige, T.E. Graedel, R. Lifset, Barbara Reck, Robert Gordon, and Stefan Pauliuk for inspiring discussions and feedback on the manuscript. Supported by NSF grant BES-0329470, the International Iron and Steel Institute, and ArcelorMittal.

Supporting Information Available Models and data used, in particular the impact of different lifetime assumptions. This information is available free of charge via the Internet at http://pubs.acs.org/.

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