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 social cost of carbon, often abbreviated SC-CO2, attempts to answer a deceptively simple question: how much economic damage, in dollars, does one additional tonne of carbon dioxide emitted today inflict across the entire future? The concept traces back to Pigouvian welfare economics, and in recent years it has moved from academic obscurity to the centre of regulatory policy, informing everything from power plant standards to fuel economy rules. In 2022, a landmark analysis in Nature by Rennert and colleagues pushed central estimates sharply upward, and the United States Environmental Protection Agency subsequently adopted estimates incorporating recent scientific advances. Yet the damage functions underpinning these figures have remained incomplete, and one of the most glaring omissions has been the effect of heat on the human capacity to work.

The physiological mechanism is well understood. As wet bulb globe temperature rises, the human body must divert more blood flow to the skin for cooling, heart rate climbs, and workers instinctively take more breaks or reduce their working intensity to avoid dangerous heat strain. Occupational health standards, including the widely used wet bulb globe temperature index maintained by the International Organization for Standardization, codify exactly how much work time is lost at given heat levels. Decades of field studies, from Indian rice harvesters to West Bengal brick workers and Hong Kong construction crews, have documented these losses in practice, and economic research has confirmed measurable impacts on output in manufacturing and on cognitive performance as well. What has been missing is a rigorous translation of this physiological and empirical evidence into the global, sector-resolved economic accounting that the social cost of carbon requires.

The new study closes that gap with an unusually detailed modelling chain. Qinqin Kong and Matthew Huber produced bias-corrected projections of wet bulb globe temperature under the CMIP6 climate model ensemble, correcting known model biases and computing heat stress metrics explicitly rather than through crude approximations, which earlier work has shown can materially misestimate labour losses. These projections cover three levels of work intensity and both indoor and outdoor conditions. The team then applied two distinct labour response functions, one based on the ISO occupational standard and another drawn from a separate empirical framework, to convert heat exposure into losses of effective labour capacity by job type, economic sector and region.

Crucially, the researchers did not simply multiply lost labour hours by wages. Instead, they fed the labour productivity shocks into a general equilibrium model built on the Global Trade Analysis Project database, allowing prices, trade flows, sectoral reallocation and other economic adaptations to buffer or amplify the initial shock. This is a key distinction, because heat stress does not hit the world economy uniformly. It concentrates in already hot, labour-intensive economies, propagates through global supply chains as the prices of agricultural and manufactured goods shift, and triggers substitutions that general equilibrium modelling can capture but simpler accounting cannot. The resulting damages were then expressed as regional damage functions, relating warming to welfare losses as a percentage of initial income, and incorporated into the GIVE integrated assessment framework used in recent official estimates of the social cost of carbon.

The headline result for labour is striking: heat-related labour productivity damages amount to US$41 per tonne of carbon dioxide emitted in 2025, with a 90 percent confidence interval running from US$1 to US$108. Losses are heavily concentrated in South, East and Southeast Asia and in Africa, regions where outdoor and physically demanding work remains a large share of employment and where cooling infrastructure is least widespread. Under an illustrative warming level of 1.7 degrees Celsius, the maps of projected labour capacity loss reveal a world of profound inequality, with tropical and subtropical working populations bearing damages that temperate, wealthy economies largely escape. This geographic concentration matters not only for equity but also for policy design, since it identifies where adaptation investments such as shaded worksites, adjusted working hours, mechanisation and expanded access to cooling would deliver the greatest returns.

The second major contribution of the study is a downward revision of agricultural damages. Previous estimates, including the authors’ own earlier work, had translated the findings of crop-yield meta-analyses into damage functions that implied agricultural losses of US$95 per tonne of carbon dioxide. The Sixth Assessment Report of the Intergovernmental Panel on Climate Change, drawing on a much larger body of evidence including process-based crop models and studies accounting for adaptation, carbon dioxide fertilisation and changing growing regions, supports substantially smaller aggregate impacts. Incorporating that assessment reduces the agricultural damage component to US$29 per tonne. The revision is a reminder that damage estimates are only as good as the underlying impact literature, and that as climate impact science matures, policy-relevant numbers must be updated rather than fossilised.

Netted together, the two revisions lower the expected 2025 social cost of carbon dioxide from US$204 to US$179 per tonne, using a 2 percent near-term discount rate in 2020 dollars. But the authors emphasise that the more important change may be the treatment of uncertainty. By building labour damages from explicit physiological data, bias-corrected climate projections and structural economic modelling, and by grounding agricultural damages in an authoritative assessment synthesis, the study substantially narrows the confidence interval around the social cost of carbon. For regulators, who must defend these figures in courtrooms and rulemaking dockets, a central estimate backed by a transparent, reproducible evidence chain is arguably worth as much as the point value itself.

The findings land at a politically charged moment, as governments weigh how heavily carbon damages should weigh in cost-benefit analysis and as the scientific community continues to expand the catalogue of climate impacts, from mortality and morbidity to energy demand and coastal inundation. This study demonstrates both directions of that expansion: adding a previously missing damage category centred on the world’s most vulnerable workers, while trimming another that had likely been overstated. The complete methodological chain, from gridded heat stress datasets and damage module code to the revised integrated assessment calculations, has been made openly available, allowing other researchers to scrutinise and extend the work. As the evidence base grows, the social cost of carbon is becoming less of a contested abstraction and more of a measurable summary of what each tonne of carbon dioxide truly costs the human economy, and the newest answer is that it costs most dearly in the sweat of those who work under the sun.

Subject of Research: Estimating the social cost of carbon dioxide by incorporating heat-related labour productivity damages and updated agricultural damage functions

Article Title: New labour and agricultural damages improve climate cost estimates

Article References: Moore, F. C., Haqiqi, I., Kong, Q., Rennels, L., Baldos, U., Ganapathi, H., Huber, M., & Hertel, T. (2026). New labour and agricultural damages improve climate cost estimates. Nature Climate Change. https://doi.org/10.1038/s41558-026-02749-z

Image Credits: AI Generated

DOI: 10.1038/s41558-026-02749-z

Keywords: social cost of carbon, heat stress, labour productivity, climate change damages, agriculture, integrated assessment modelling, CMIP6, wet bulb globe temperature, general equilibrium, Nature Climate Change, climate economics, adaptation