(CNSNews.com) – Cement, the ubiquitous material used to build roads, buildings and other infrastructure, absorbs about one billion tons of atmospheric carbon dioxide (CO2) annually, according to a new study published Monday in the journal Nature Geoscience.
But concrete carbonation is “not currently considered in emissions inventories” kept by the U.N. Intergovernmental Panel on Climate Change (IPCC), according to the study’s co-authors, an international team of researchers led by Professor Dabo Guan of the U.K.’s University of East Anglia.
The study found that cement’s natural carbonation process not only offsets the fossil fuel emissions released during its production, it also “represents a large and growing net sink of CO2” that has not been taken into account by the IPCC.
“It is well known that the weathering of carbonate and silicate materials removes CO2 from the atmosphere on geologic timescales,” said the study, entitled Substantial Global Carbon Uptake by Cement Carbonation.
“However, the potential for removal by the weathering of cement materials has only been recently recognized. Our results indicate that such enhanced weathering is already occurring on a large scale; existing cement stocks worldwide sequester approximately one billion tons of atmospheric CO2 each year.”
The study, which was conducted in China by China Emission Accounts and Datasets (CEADs), explained that the physiochemical process of carbonation, which absorbs CO2 into the pores of cement materials such as concrete and mortar, is “a slow process that takes place throughout the entire life cycle of cement-based materials,” and even continues when a cement structure is demolished and the concrete is repurposed.
“Existing cement is a large and overlooked carbon sink and future emissions inventories and carbon budgets may be improved by including this,” said Prof. Guan.
The research team estimated that cement reabsorbed 4.5 gigatons of carbon (GtC) worldwide between 1930 and 2013, offsetting 43 per cent of the emissions from its production over the same period, not counting emissions associated with fossil fuel use.
About 44 per cent of cement process emissions produced each year between 1980 and 2013 were offset by the annual cement “sink”, the study found. And because demolition exposes new surfaces to atmospheric CO2, cement continues to absorb it even when a structure has been torn down.
“We suggest that if carbon capture and storage technology were applied to cement process emissions, the produced cements might represent a source of negative CO2 emissions,” Guan stated.
“Policymakers might also investigate ways to increase the completeness and rate of carbonation of cement waste, for example as a part of an enhanced weathering scheme, to further reduce the climate impacts of cement emissions,” he added.
Since the study shows that cement sequesters about one billion tons of CO2 annually that the IPCC has not taken into consideration, wouldn't they have to adjust their numbers accordingly and decrease he amount of CO2 reductions necessary to prevent global warming? CNSNews asked Guan.
“Current emission inventory adopted by IPCC is territorial emissions approach, which does not account for all emissions sources/sinks,” Guan replied in an email.
“We (CEADs, China Emission Accounts and Datasets – a group of researchers from different countries globally,) have been attempting to further develop the emission accounting method, test robustness and improve emission estimation accuracy over past decades. Cement natural carbonation over life-time as carbon sink is a brand new research we present here,” he continued.
“IPCC and global climate change community have been advocated emission data accuracy and transparencies. The Paris Adoption (so-called Paris Agreement for Climate Change) formally wrote in the Article 4.1 as: ‘Parties shall account for their nationally determined contributions. In accounting for anthropogenic emissions and removals corresponding to their nationally determined contributions, Parties shall promote environmental integrity, transparency, accuracy, completeness, comparability and consistency, and ensure the avoidance of double counting, in accordance with guidance adopted by the Conference of the Parties serving as the meeting of the Parties to the Paris Agreement.’
“I hope our studies will provide quantitative evidence for improving IPCC emission inventory method and data,” Guan added.