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Cement Production. The emissions for cement production include both the process emissions from the calcination of limestone and the combustion emissions from the burning of fuels. The process emissions consist of CO₂ generated during the calcination of limestone in a kiln to produce clinker.  Emissions from calcination and the combustion of fossil fuels each account for about one-half of the total CO₂ emissions from kilns.  Reported emissions from the cement production subsector have increased by 19.6 percent, from 55.5 MMT CO₂e in 2011 to 66.4 MMT CO₂e in 2020. From 2019 to 2020, emissions decreased slightly, about 1 percent, from 67.1 to 66.4 MMT CO₂e. Increases and decreases in clinker production can be attributed to an increase or decrease in demand for cement in new residential and non-residential construction. According to the USGS [1], cement production was temporarily idled in many countries and localities in response to national lockdowns imposed in response to the COVID-19 pandemic. Disruptions to construction corresponded with reduced cement demand, and some planned cement plant openings and expansions were delayed. As shown in the table below, there is a high correlation between clinker production and emissions.

Lime Manufacturing. The emissions for lime manufacturing include both the process emissions and the combustion emissions from the burning of fossil fuels. The process emissions consist of CO₂ generated during the calcination of limestone. Major uses of lime include industrial, chemical, and environmental applications. Reported emissions from the lime production subsector have remained relatively steady as demand for lime has remained fairly stable. The emissions have varied from a low of 27.7 MMT CO₂e reported in 2016 to a high of 31.6 MMT CO₂e in 2014. Emissions for this sector increased between 2016 and 2018 likely due to increased lime production.[2] Emissions decreased slightly in 2019 and continued to decrease in 2020 down to 25.1 MMT CO₂e due to a decrease in lime production since 2018. [2] 

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