Comprehensive update: The carbon content of global material stocks

A new study by BOKU researchers shows that the societal carbon stock reaches a geologically relevant size in the Anthropocene – integration into future balances of the global carbon cycle proposed.

Societal activities are profoundly changing the global carbon cycle. The accumulation of carbon in the atmosphere is driving global warming and jeopardizing safe survival on the planet. At the same time, human societies are accumulating enormous stocks of materials, for example in buildings and infrastructure. This societal carbon pool – i.e. the total amount of carbon contained in material stocks – is currently being discussed as a potential carbon store or sink, as it can bind carbon in the long term and thus keep it out of the atmosphere.

In the study “Society’s material stocks as carbon pool: An economy-wide quantification of global carbon stocks from 1900-2015“, which has just been published in Environmental Research Letters, researchers from BOKU’s Institute of Social Ecology (SEC) now present new findings on the development and global distribution of carbon in societal material stocks such as buildings and infrastructure.

The study was conducted because the carbon content of materials used in buildings and infrastructure varies, so the total amount of carbon stored in societal material stocks depends on which materials (wood, paper, concrete, steel, glass, etc.) they are made of. “This study presents a comprehensive quantification of societal carbon stocks, which makes an important contribution to addressing the current climate crisis in light of human interventions in the global carbon cycle and the massive build-up of material stocks,” said lead author Lisa Kaufmann from the SEC, explaining the new findings.

New results

Until now, little was known about the size, composition, distribution and development of global socio-economic carbon stocks. These were now calculated for the first time in the study for the period from 1900 to 2015, distinguishing between nine world regions and a total of eight carbon-containing components (e.g. wood products, plastic), whereas materials that do not contain carbon (such as glass) did not have to be taken into account.

The global social carbon stock increased 17-fold from 2.5 PgC* in 1900 to 42.0 PgC in 2015. At the beginning of the 20th century, less than a quarter of the carbon contained in societal material stocks (0.6 PgC) was found in inert, inorganic compounds, from which the carbon remains stored over long periods of time. In 2015, however, the proportion of inert carbon was already almost two thirds (25.2 PgC). These carbon compounds, for example in limestone gravel, are only involved in the global carbon cycle over very long (geological) periods of time and are not directly relevant for climate policy. Active carbon from biomass and fossil raw materials, on the other hand, can be potentially climate-relevant and only grew 9-fold from 1.9 to 16.8 PgC in the same period. To illustrate: this amount of carbon accumulated over 115 years corresponds to only around 4% of the amount of carbon that would have to be removed from the atmosphere by 2100 to meet the Paris target of limiting global warming to 1.5°.

The annual net growth of active carbon stocks in society amounted to 0.49 PgC. However, this carbon uptake is offset by the release of 9.9 PgC from fossil fuels and industrial processes; the sequestration of carbon relevant to the atmosphere in the short term therefore only corresponds to around 5% of emissions from fossil energy. An increase in the annual net growth of biomass components that sequester carbon from the atmosphere, such as wood or plastics from renewable resources, can have negative impacts on ecosystems, biodiversity and food security.

Holistic perspective required for CO2 accounting

The researchers’ conclusion to integrate societal carbon stocks into future assessments of the global carbon cycle underlines the importance of a holistic perspective on social and natural carbon stocks, because the study shows, among other things, that the global societal carbon stock has reached a relevant level – namely that of the carbon stored in coastal ecosystems. According to the researchers, societal carbon stocks should therefore be integrated into future assessments of the global carbon cycle. “Although the study shows that the contribution of annual societal carbon increases to mitigating global warming is rather limited in view of continuing CO2 emissions, the total societal carbon stock has reached a geologically relevant size of about 42 PgC in 2015 and can be considered another feature of the Anthropocene era,” concludes Lisa Kaufmann.