Abstract Background The CO2 released by humans and livestock through digestion and decomposition is an important part of the urban carbon cycle, but is rarely considered in studies of city carbon budgets since its annual magnitude is usually much lower than that of fossil fuel emissions within the boundaries of cities. However, human and livestock respiration may be substantial compared to fossil fuel emissions in areas with high population density such as Manhattan or Beijing. High-resolution datasets of CO2 released from respiration also have rarely been reported on a global scale or in cities globally. Here, we estimate the CO2 released by human and livestock respiration at global and city scales and then compare it with the carbon emissions inventory from fossil fuels in 14 cities worldwide. Results The results show that the total magnitude of human and livestock respiration emissions is 38.2% of the fossil fuel emissions in Sao Paulo, highest amongst the 14 cities considered here. The proportion is larger than 10% in cities of Delhi, Cape Town and Tokyo. In other cities, it is relatively small with a proportion around 5%. In addition, almost 90% of respiratory carbon comes from urban areas in most of the cities, while up to one-third comes from suburban areas in Beijing on account of the siginificant livestock production. Conclution The results suggest that the respiration of human and livestock represents a significant CO2 source in some cities and is nonnegligible for city carbon budget analysis and carbon monitoring. 426 cbmjournal Carbon Balance and Management Carbon Balance Manag BMC PMC9635100 9635100 9635100 36326963 10.1186/s13021-022-00217-7 The impact of human and livestock respiration on CO 2 emissions from 14 global cities Cai Qixiang 1 ✉ Zeng Ning 2 Zhao Fang 3 Han Pengfei 1 Liu Di 1 Lin Xiaohui 4 Chen Jingwen 5 1 State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China 2 Department of Atmospheric and Oceanic Science, and Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD USA 3 Key Laboratory of Geographic Information Science (Ministry of Education), School of Geographic Sciences, East China Normal University, Shanghai, China 4 State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academ y of Sciences, Beijing, China 5 State Key Laboratory of Hydrology- Water Resources and Hydraulic Engineering, Hohai University, Nanjing, China ✉ Corresponding author. Here, we estimate the CO 2 released by human and livestock respiration at global and city scales and then compare it with the carbon emissions inventory from fossil fuels in 14 cities worldwide. Results The results show that the total magnitude of human and livestock respiration emissions is 38.2% of the fossil fuel emissions in Sao Paulo, highest amongst the 14 cities considered here. The proportion is larger than 10% in cities of Delhi, Cape Town and Tokyo. In other cities, it is relatively small with In addition, almost 90% of respiratory carbon comes from urban areas in most of the cities, while up to one-third comes from suburban areas in Beijing on account of the siginificant livestock production. Conclution The results suggest that the respiration of human and livestock represents a significant CO 2 source in some cities and is nonnegligible for city carbon budget analysis and carbon monitoring. Supplementary Information The online version contains supplementary material available at 10.1186/s13021-022-00217-7. 1 The process of urban material metabolism with crop production, the digestion of food and feedstuff by humans and livestock, and finally the release of carbon to the atmosphere via respiration However, CO 2 from human and livestock respiration is often neglected due to its perceived small magnitude compared to fossil fuel emissions (FFE) from the burning of fuels for electricity, heating and industrial purposes, other industrial processes and ground transportation within city boundaries [ 8 , 9 ]. Such a relatively high proportion is mainly contributed by the significant livestock production in suburban area, wchich accounts for 80% of the total area. Therefore, in studies with high-precision CO 2 concentration measurements, the stations located in suburban areas of cities such as Beijing, Delhi and Cape Town should also be taken into consideration [ 69 ]. Discussion Carbon monitoring in urban areas has shown that the partern of human metabolism can partially explain the diurnal pattern of CO 2 flux, as well as differences in CO 2 flux between working days and non-working days, in densely populated urban areas [ 58 , 59 ]. The research of Ciais et al. The PAL recommended by the FAO/WHO/UNU Expert Committee in 1985 was defined in three levels: the minimum was set at 1.55 and 1.56 BMR for men and women, while the highest was defined as 2.10 and 1.82 BMR for men and women, respectively [ 33 ]. Research also showed that the PAL were not significantly different between age groups[ 65 ]. Due to lack of data, we roughly assume that the average daily activity is at the lowest level since most people do not have long-term high-intensity activity. The carbon emissions from respiration per individual in this study are only a first-order approximation based on the above assumption. As a result, their estimated annual averaged global carbon emissions from human respiration is approximately 1.2 Gt C yr − 1 [ 66 ] from 1990 to 2005, which is much greater than the value estimated in this study (0.54 Gt C yr − 1 ). Additionally, their estimation of livestock respiration is approximately 0.8 Gt C yr − 1 [ 66 ], which is comparable with this study (0.62 Gt C yr − 1 ).