On a planet with a diameter of 12,700 km, a mass of 5.9 trillion (1 followed by 21 zeros) tons, moving at a speed of 107,000 km/h around the sun, an average human weighing 62 kg can feel very small. Yet humanity affects the composition of Earth's atmosphere and climate and mobilizes huge amounts of matter every year. Indeed, if the total mass of humanity (500 million tons) is insignificant, the mass of its infrastructure is far from it.
A very heavy human infrastructure
The year 2020 marked the point where the anthropogenic mass exceeded the total mass of the biomass on Earth. This anthropogenic mass is defined as the mass of all manufactured objects and includes metals, rocks, cement, wood, glass and plastic. The Earth biomass weight is estimated at about 1,100 billion tons (Gt). A figure already strongly affected by human activities since studies estimate that agriculture and deforestation have divided by 2 the total mass of plants present on Earth. The net primary productivity, i.e. the quantity of carbon fixed by photosynthesis that forms the biomass, is estimated at about 110 billion tons of carbon per year (including the oceans). If we consider all the terrestrial biomass growing each year, the energy converted by photosynthesis corresponds to 5 times the primary energy consumed by humanity.
Adding the mass of all buildings and infrastructures built since 1900, the figure of 1,100 Gt was reached in 2020. This figure has typically doubled every 20 years since 1900. As for the breakdown, concrete (including sand) accounted for about 50% of the total, and metals for about 4%. For metals, the inventory is largely dominated by iron (the main constituent of steel) which accounts for 94% in mass of all extracted metals. These quantities are only a portion of the mass excavated and extracted to recover metals. For example, if a copper ore has a grade of 2%, producing one ton of copper requires extracting a mass 50 times higher. Taking this into account and not only the final amount of metals, the anthropogenic mass would have exceeded the total amount of biomass 45 years earlier. If these figures have a rather symbolic side, and their estimation is subject to strong uncertainties, they have the merit of highlighting our strong dependence on natural resources.
The economy is far from circular
The Circularity Gap Report details the amount of materials entering the global economy annually. In 2017, this amount reached 100 billion tons-which represents about 13.4 tons per capita (with obviously very large disparities). 50% of this mass comes from minerals such as sand, clay, various rocks. Biomass represents about 25 billion tons which includes agricultural production and wood exploitation. For reference, the world production of cereals in 2018 was 2.7 billion tons. 15 billion tons of fossil fuels (coal, natural gas, oil) are used every year, mostly for energy. About 12% of the oil produced is used for chemicals. Only 8.6% of the total is recycled, while the amount buried in landfills is 11.2 Gt.
The amount of material used is increasing at a rate of about 3% per year, and if the current trend continues it would reach 177 Gt by 2044. To put this exponential increase in perspective, China produces as much cement (4.6 Gt) in 2 years as the United States did in the entire 20th century. At the current rate, it takes only 16 years to produce as much steel in the world as it did during the last century. This extraction has a high energy cost: about 10% of the world's energy consumption is dedicated resource extraction and processing, an amount that is bound to increase for metals as ore grades decline. The environmental impact is also high, particularly on biodiversity and water reserves.
A growing dependence on metals
This dependence is not likely to end, especially for metals. The decarbonization of energy infrastructures and transportation will require huge quantities of metals. The International Energy Agency predicts, for example, that the demand for metals for energy could increase by a factor of 2 to 4 by 2040. This increase could reach a factor of 10 to 40 for metals such as lithium, which is needed for batteries. Very large investments will be necessary to meet the demand and to increase the extraction capacities. It is interesting to note, however, that if we consider the total amount of material excavated in the extraction of metals and fossil fuels, the energy transition will lead to a decrease in the total amount of material extracted for the energy and transportation sectors. A somewhat counterintuitive result, largely related to the huge amounts of fossil resources we use each year- by weight 40% of maritime trade (around 11 billion tons per year in total) consists of fossil fuels…
Will there be enough metals for the energy transition?
The argument of humanity running out of the critical minerals required for the energy transition is often brought forward to demonstrate its impossibility. It is first important to define things properly: resources are the part of a geological stock whose exploitation is deemed potentially feasible – reserves are the part of it that can be exploited under current standards. Those are dynamic entities, which are not only defined in geological terms but also vary with the socio-economic context. If one takes the example of copper, since 1960 the ratio between known reserves and annual production has been between 25 and 40 i.e. that the reserves have increased as the consumption increased. This is true for lithium also whose reserves have almost doubled since 2019, and for many metals.
The problem of the critical minerals is not so much a problem of stocks (resources) than a problem of flux in a context of a strongly growing demand. Since the mining industry has relatively long lead times the risk in the next decade is that the production cannot keep up with demand. There is therefore a strong drive to reduce the future demand using strategies such as substitution (the changes in battery chemistry to reduce cobalt use is telling), material efficiency or recycling- the latter can only have a strong impact once the demand stabilizes.
One should also be aware that many technologies become more efficient (see the example of PV) and long-term demand projections also depend on technology choices so different scenarios can show very different forecasts.
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