Accounting for Global Carbon Dioxide Production from Human Metabolism between 1985-2015: A Modelling Study

Atkinson, G ORCID: 0000-0002-5459-9042 Accounting for Global Carbon Dioxide Production from Human Metabolism between 1985-2015: A Modelling Study. The Lancet Planetary Health. ISSN 2542-5196 (Accepted)

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Abstract

Background
Human activity is a dominant driver of global carbon emissions, yet one universal source – human metabolism – has never been quantified using free-living measurements of carbon dioxide (CO2) production at scale. We aimed to describe the contribution of human metabolism to global CO2 emissions between 1985-2015.

Methods
Using the largest database of doubly labelled water (DLW) measurements currently available, covering thousands of individuals across all ages (range: <1 to >100 years), body size (range: 2.4 to 192.4 kg body mass) and continents, we first allometrically modelled human CO2 production (kg/year) using measurements available for 4479 female and 2277 male participants from the IAEA DLW Database to derive predicted estimates of human CO2 production adjusted for differences in body mass and sex. Second, by combining predicted estimates based on allometric scaling of CO2 production for body mass with available population demographic information, generalised additive models were used to describe the 30-year progression of human body mass and per capita, and global CO2 production using time-series country-specific measurements from 1985 to 2015 with population-level global human metabolic CO2 production summarised as cumulative sum.

Findings
We revealed that human metabolic CO2 production approximately doubled over a 30-year period, from ~1 to >2 gigatonnes/year. This increase was driven mostly by population growth (>60%) with a more minor contribution from increases in body mass. Per capita sex differences equalise at the population level, and continental differences reflect population shifts rather than physiological differences, with Asia contributing more than all other regions combined.

Interpretation
These data suggest that human metabolism is a quantitatively important component of the fast carbon cycle. With a projected peak global population in the mid-to-late 21st century, metabolic CO2 production will increasingly contribute to global carbon fluxes. Human metabolic CO2 production warrants inclusion in carbon system modelling to enhance precision and fidelity.

Item Type:	Article
Uncontrolled Keywords:	Research Institute for Sport & Exercise Sciences (RISES); 4101 Climate change impacts and adaptation; 4104 Environmental management; 4206 Public health
Subjects:	G Geography. Anthropology. Recreation > GE Environmental Sciences R Medicine > RC Internal medicine > RC1200 Sports Medicine
Divisions:	Sport and Exercise Sciences
Publisher:	Elsevier
Date of acceptance:	17 September 2026
Date Deposited:	18 Sep 2026 14:00
Last Modified:	18 Sep 2026 14:00
URI:	https://researchonline.ljmu.ac.uk/id/eprint/29468

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