Global socioeconomic material stocks rise 23-fold over the 20th century and require half of annual resource use

Abstract

Human-made material stocks accumulating in buildings, infrastructure, and machinery play a crucial but underappreciated role in shaping the use of material and energy resources. Building, maintaining, and in particular operating in-use stocks of materials require raw materials and energy. Material stocks create long-term path-dependencies because of their longevity. Fostering a transition toward environmentally sustainable patterns of resource use requires a more complete understanding of stock-flow relations. Here we show that about half of all materials extracted globally by humans each year are used to build up or renew in-use stocks of materials. Based on a dynamic stock-flow model, we analyze stocks, inflows, and outflows of all materials and their relation to economic growth, energy use, and CO₂ emissions from 1900 to 2010. Over this period, global material stocks increased 23-fold, reaching 792 Pg (±5%) in 2010. Despite efforts to improve recycling rates, continuous stock growth precludes closing material loops; recycling still only contributes 12% of inflows to stocks. Stocks are likely to continue to grow, driven by large infrastructure and building requirements in emerging economies. A convergence of material stocks at the level of industrial countries would lead to a fourfold increase in global stocks, and CO₂ emissions exceeding climate change goals. Reducing expected future increases of material and energy demand and greenhouse gas emissions will require decoupling of services from the stocks and flows of materials through, for example, more intensive utilization of existing stocks, longer service lifetimes, and more efficient design.

Keywords: carbon emission intensity; circular economy; manufactured capital; material flow accounting; socioeconomic metabolism.

Fig. 1.

Development of global material stocks and flows from 1900 to 2010. (A) Annual global extraction of materials by use and share of stock-building materials in total extraction (right axis). (B) Development of global in-use stocks of materials by 12 main material groups. (C) Global material stocks in 2010 including uncertainty ranges (note that the scales in C differ by a factor of 10). (D) Development of total stock per capita in the group of industrial countries, China, and the rest of the world (RoW). (E) Global end-of-life outputs from discarded stocks and recycling input rate (i.e., share of recycled and down-cycled end-of-life outputs from stocks in total inputs to stocks). Note that B, C, and E share the same legend.

Fig. 2.

Development of global stocks in relation to GDP, energy use, and CO₂ emissions 1900–2010. (A) Global stock productivity (GDP/material stock) and material use productivity (GDP/annual material consumption, right axis). (B) Energy and carbon emission intensity of material stocks. Total primary energy supply (TPES) and CO₂ emissions from fossil fuel use per megagram of material stock. Material use (domestic material consumption) is in megagrams (9), GDP in constant international dollars of 1990 (45), CO₂ emissions in kilograms of C (46), and TPES in gigajoules (9).

Fig. 3.

Dynamics of stocks and flows in the industrial countries, China, and the rest of the world (RoW). (A) Distribution of global stocks across country groups. (B) Annual net additions to stock.