The scale of the existing system is staggering. The team estimates that in 2024 the world’s mobility infrastructure contained roughly 355 billion metric tons of materials, with an uncertainty range of 255 to 455 billion tons. Aggregates such as sand and gravel account for 74 percent of that mass, followed by concrete and asphalt. Lower-class roads, the local and rural routes that rarely attract attention, hold nearly half of all the material, while high-class roads such as motorways hold another 37 percent. Rail-based infrastructure, including subways, trams, bridges and station buildings, represents only 6 percent of the total mass but consumes a remarkable 68 percent of all the steel embedded in mobility networks. Parking, fueling stations and airport runways contribute less than 3 percent.

What makes the study politically explosive is its mapping of inequality. Per-capita infrastructure stocks range from about 5 metric tons in densely populated, low-income regions such as Sub-Saharan Africa and South Asia to nearly 500 tons in affluent, low-density regions of North America and Western Europe. In length terms, that spans from less than one meter of infrastructure per person to more than 230 meters. The researchers point to earlier work suggesting that well-being gains from mobility infrastructure saturate at around 100 tons per capita, a threshold already exceeded by roughly 20 percent of countries. If the rest of the world converged on that decent-mobility level, global stocks would triple to about 1,037 billion tons by 2060, with South Asia seeing an eightfold increase and Sub-Saharan Africa a sevenfold increase.

Methodologically, the study is a marriage of two modelling traditions that rarely speak to each other. The team first mapped global infrastructure at a resolution of 10 by 10 meters using OpenStreetMap data, which earlier research has shown to be more than 80 percent complete for roads, and harmonized the features into 37 infrastructure classes. They converted lines and points into areas using region-specific average widths validated against satellite imagery, then multiplied each class’s area by material intensity factors covering ten materials from steel and copper to timber and plastics. This produced the baseline stock for 2024. Future stocks were projected by matching each country’s infrastructure to vehicle-kilometer trajectories from the MESSAGEix-Transport integrated assessment model across 12 world regions and seven transport modes, under the Shared Socioeconomic Pathway ‘middle of the road’ scenario.

The second half of the workflow is what gives the study its carbon teeth. Annual material inflows were calculated from the net change in stocks plus maintenance flows derived from class-specific lifetimes, using a ‘leaching’ approach in which infrastructure gradually wears out rather than disappearing at a single end-of-life date. These flows then feed into MESSAGEix-Materials, an economy-wide model that tracks materials from extraction through industrial processing to recycling and waste, and computes the embodied carbon dioxide of producing concrete, asphalt, iron and steel, and aluminum. In the reference scenario, annual material flows reach 23 billion tons by 2060, split roughly equally between expansion and the maintenance and replacement of existing networks, with about 69 percent of maintenance concentrated in higher-income countries whose stocks are already saturated.

The headline numbers on carbon are sobering. Cumulative embodied emissions from 2024 to 2060 amount to about 11 gigatons of carbon dioxide in the reference scenario, equivalent to roughly 1.0 to 6.2 percent of the remaining carbon budget for holding warming to 2 degrees or 1.5 degrees respectively. Under the global convergence scenario, emissions climb 76 percent to 19 gigatons. Most striking is the rail paradox: a worldwide modal shift from road to rail, often promoted as a climate solution, would push embodied emissions up 241 percent to 37 gigatons of carbon dioxide, because railways are extraordinarily hungry for steel, concrete, aluminum and copper. In that scenario, rail infrastructure stocks grow fourteenfold to 300 billion tons, with copper stocks increasing 21-fold and timber, largely for railway sleepers, growing 14-fold.

Not every demand-side measure moves the needle. Halving the vehicle fleet through car sharing, and fully electrifying the passenger fleet, change total stocks by less than 1 percent, because parking and charging infrastructure are a trivial share of total mass. The single most powerful lever is reducing mobility demand itself, particularly in high-income countries. An income-tiered global mobility reduction holds 2060 stocks to 520 billion tons, well below the reference trajectory, and cuts cumulative embodied emissions by 44 percent to 6 gigatons. The researchers are careful to frame their projections as exploratory ‘what-if’ scenarios rather than forecasts, noting that the relationship between demand and infrastructure is non-linear; sensitivity tests in which high-intensity regions utilize infrastructure more intensively before expanding yield stocks 10 to 35 percent below reference levels.

Supply-side measures alone disappoint. Bundles of circular economy and decarbonization options, including material substitution, higher recycling rates, fuel switching in heavy industry and carbon capture and storage, reduce embodied emissions by only 4 to 8 percent when deployed without broader climate policy. But the picture changes dramatically when they are combined with economy-wide climate policy consistent with a 67 percent chance of staying below 2 degrees. Pairing that policy package with the reference or convergence scenarios cuts cumulative emissions by 40 to 47 percent. Most importantly, the fully integrated scenario, combining mobility reduction, rail expansion, enhanced recycling and industrial decarbonization, delivers a 63 percent reduction in embodied emissions while still providing adequate infrastructure for a growing and urbanizing world, helping to offset the carbon cost of building the public transport systems needed to slash operational emissions.

The study’s authors argue that the decisive question is not how much infrastructure gets built but what kind and where, and that urban form is the hidden variable. Decentralized, car-oriented development entrenches automobile dependence, while dense, well-planned cities enable efficient public and active transport with far lower infrastructure requirements per person served. Urban mobility already accounts for 40 percent of global passenger transport carbon emissions, and the urban fabric laid down in South Asia and Sub-Saharan Africa over the coming decades will lock in mobility patterns for a century. The researchers point to empirical evidence from Vienna and scenario analyses for Indian cities showing that shifts toward public and non-motorized transport can substantially reduce resource use and emissions, and to concepts such as Barcelona-style ‘superblocks’ and transit-oriented development as spatial strategies that make car-free life convenient rather than coercive.

There is also a deeper tension the study forces into the open. Operational emissions from vehicles, estimated at roughly 260 to 300 gigatons of carbon dioxide cumulatively through 2060, dwarf infrastructure’s embodied emissions by nearly thirty times, which is why the latter has been ignored. Yet infrastructure and operations are coupled: every new kilometer of road stimulates the very traffic that makes decarbonization harder, a dynamic known as induced demand, vividly illustrated by the Belt and Road initiative opening new freight corridors across Eurasia. The authors stress that replacing motorized trips with walking and cycling in dense urban settings requires comparatively little material investment and delivers public health co-benefits through cleaner air and more physical activity. Their bottom line is that neither demand reduction nor cleaner production alone can reconcile the coming infrastructure boom with climate goals; only an integrated strategy, planned jointly with land use, can deliver mobility for all without mortgaging the carbon budget.

Subject of Research: Global material stocks and embodied carbon emissions of future road and rail mobility infrastructure expansion

Article Title: Material and carbon implications of future mobility infrastructure expansion around the world

Article References: Baumgart, A., Ünlü, G., Grammer, B., Javaid, A., Maczek, F., Krausmann, F., Krey, V., & Wiedenhofer, D. (2026). Material and carbon implications of future mobility infrastructure expansion around the world. Journal of Industrial Ecology, 30(4), 1935-1949. https://doi.org/10.1007/s44498-026-00132-x

Image Credits: AI Generated

DOI: 10.1007/s44498-026-00132-x

Keywords: mobility infrastructure, material stocks, embodied emissions, carbon budget, railways, roads, circular economy, decarbonization, urban form, OpenStreetMap, integrated assessment modelling, Global South

The research tackles a long-standing blind spot in climate economics. When a country exports goods, the emissions generated in producing them are counted in the exporting nation’s territorial inventory, even though the goods are consumed elsewhere. This mismatch, known as the problem of embodied or trade-embedded emissions, has been studied extensively since Davis and Caldeira’s landmark consumption-based accounting work, but most analyses treat exports as a single undifferentiated flow. Ünal and Erkök argue that this flattening hides the very information policymakers need. An export of finished consumer goods and an export of intermediate components that feed a partner’s own industrial production have very different implications for how carbon pricing, border adjustments, or supply chain regulations will shift emissions between countries.

To unpack these differences, the authors deploy an environmentally extended input-output framework built on the Eora Global Supply Chain Database, combined with a technique called the Multi-Stage Hypothetical Extraction Method. Hypothetical extraction is a thought experiment rendered in matrix algebra: the analyst mathematically removes a sector, or a demand channel, from the economy’s input-output structure and measures how much output and, in this case, how much carbon dioxide the rest of the system loses as a result. The difference between the original economy and the extracted one quantifies the sector’s total systemic importance, capturing both its direct emissions and the emissions embedded in all the upstream linkages that depend on it. The multi-stage refinement goes further by decomposing exports into intermediate goods and final goods, and by splitting final demand into household consumption, government expenditure, and investment channels, allowing emissions to be traced along distinct domestic production stages for each destination market.

The study focuses on six major trading partners of Türkiye: France, Germany, Iraq, Italy, the United Kingdom, and the United States. This selection spans the European Union markets that dominate Turkish trade, the transatlantic relationship, and a neighboring energy economy, providing a diverse test bed for the method. For each partner, the researchers calculated the carbon dioxide emissions embodied in Turkish exports and, crucially, a set of efficiency measures that relate those emissions to the economic value delivered. It is the efficiency dimension that produced the study’s most alarming headline result: a systemic deterioration in carbon dioxide efficiency across most destinations, meaning that progressively more emissions are being generated per unit of export value delivered to these markets.

The structural decomposition reveals that intermediate goods typically dominate the emissions profile of Turkish exports. This matters because intermediate goods occupy a particularly awkward position in climate policy. They cross borders as inputs to further production, so their embodied carbon will only be fully accounted for when the final product is eventually sold, often in a third country. Under mechanisms such as the European Union’s Carbon Border Adjustment Mechanism, which is designed to prevent carbon leakage by pricing the embedded emissions of imports, the treatment of intermediate goods remains one of the most contested design questions. The finding that Türkiye’s export emissions concentrate in these upstream flows suggests that the country’s industrial base is deeply integrated into European and global value chains in ways that make it structurally exposed to any tightening of carbon accounting at the border.

The United Kingdom emerges as a distinctive case. Unlike the other partners, where either intermediate or final goods tend to dominate, the UK’s import profile from Türkiye shows a broad reliance on both categories simultaneously. This dual dependence means that British demand pulls carbon out of the Turkish economy through two separate channels at once, amplifying the total systemic liability and complicating any single-lever policy response. As the UK develops its own post-Brexit carbon border policies, the study’s results imply that Turkish exporters will face pressure from both ends of their product mix rather than from a single vulnerable segment.

Perhaps the most striking results concern the role of government demand, which behaves in sharply different ways depending on the partner. In France and Italy, state-procured government expenditures drive intense emissions liabilities, channeled primarily through Türkiye’s petroleum and chemical sectors. In other words, when the French or Italian state buys goods with Turkish content, the production cascade that follows leans heavily on some of the most carbon-intensive links in the Turkish industrial chain. By contrast, in Iraq and the United States, government expenditure acts less as a direct trigger and more as a deep systemic dependency, anchored in the utility and heavy manufacturing sectors. These partner-specific patterns demonstrate that the same category of final demand can produce qualitatively different carbon consequences depending on the industrial structure it activates, a nuance that aggregate trade-emissions statistics completely obscure.

Underlying all of these patterns is a remarkably concentrated industrial structure. Four sector groups account for the dominant shares of the efficiency effects the authors measure: textiles, transport equipment, petroleum and chemical products, and electricity and gas provisions. This concentration is both a vulnerability and an opportunity. It is a vulnerability because it means Türkiye’s export carbon footprint is not broadly distributed across the economy but is instead pinned to a handful of energy-intensive nodes, several of which are precisely the sectors most likely to be targeted by carbon border measures and by competition from lower-carbon producers. It is an opportunity because targeted interventions at a small number of chokepoints, such as decarbonizing the electricity and gas supply that feeds industrial production, or modernizing petroleum and chemical processing, could deliver disproportionate improvements in the carbon efficiency of the entire export apparatus.

The authors draw a clear policy conclusion from this structure: mitigation efforts must be targeted and partner-specific rather than uniform. Because the emissions liabilities attached to French government procurement arise through different sectors than those attached to American systemic dependencies, a single national decarbonization strategy will not address all exposures equally. Instead, the findings argue for industrial policies and technological investments calibrated to the specific production stages and demand channels that generate the largest efficiency losses for each destination. The open availability of the study’s processed datasets and analysis code in a public GitHub repository lowers the barrier for other researchers to extend the multi-stage extraction approach to other economies, and the method itself, which links classical linkage analysis in the tradition of Hirschman and Rasmussen to modern environmental accounting, offers a template for dissecting how carbon flows through the layered stages of globalized production.

As carbon border regulations spread and trading partners begin pricing the emissions embedded in imports, studies of this kind are likely to become essential reading for policymakers in emerging industrial economies. The Turkish case shows that the question is no longer simply how much carbon a country exports, but through which sectors, along which production stages, and in response to whose demand. Answering that question with the granularity that the multi-stage hypothetical extraction method provides may determine which economies adapt smoothly to a carbon-constrained trading system and which find their industrial linkages transformed into liabilities overnight.

Subject of Research: Export-embodied CO2 emissions and carbon leakage in Turkiye's trade analyzed via multi-stage hypothetical extraction

Article Title: Sectoral linkages and carbon leakage: A multi-stage hypothetical extraction analysis of export-embodied emissions

Article References: Ünal, E., & Erkök, B. (2026). Sectoral linkages and carbon leakage: A multi-stage hypothetical extraction analysis of export-embodied emissions. Journal of Industrial Ecology, 30(4), 2189-2207. https://doi.org/10.1007/s44498-026-00149-2

Image Credits: AI Generated

DOI: 10.1007/s44498-026-00149-2

Keywords: carbon leakage, embodied emissions, input-output analysis, hypothetical extraction method, Turkiye, international trade, CO2 efficiency, intermediate goods, carbon border adjustment, industrial policy, global value chains, Eora database