Resolving the land carbon accounting riddle: consistent metrics for countries and products

Historically, land-use change has contributed to approximately one-third of anthropogenic carbon dioxide (CO2) emissions, demonstrating the critical role land use can play in rebalancing the global carbon cycle. However, the continued occupation of land by human activities delays the regeneration of potential carbon stocks in terrestrial ecosystems – a dynamic largely overlooked that remains underrepresented in climate accounting, despite the widespread use of Global Warming Potentials (GWPs). Inconsistencies in the application of GWPs further challenge the accurate assessment of land-use impacts. This study introduces a new metric – GWPland – for product-level carbon footprinting and life cycle assessment (LCA), which uses differentiated impulse response functions (IRFs) to represent the delayed carbon regeneration resulting from land occupation. By computing land use IRFs, we can calculate Absolute Global Warming Potentials (AGWPs) for various occupation and regeneration periods, thus enabling the derivation of GWPland factors over 20-, 100- and 500-year horizons. GWPland increases non-linearly with occupation duration and approach 1 when the occupation time exceeds the GWP horizon or regeneration is indefinitely delayed. At the country level, we propose three adjusted GWP metrics – GWPALS (all land sinks), GWPPLS (partial land sinks), and GWPNLS (no land sinks) – to improve consistency with national greenhouse gas inventory (NGHGI) reporting. These variants reduce default (IPCC AR6) non-CO2 GWP values by up to 13% (GWPPLS) and 21% (GWPNLS), helping to avoid double-counting of the terrestrial sink. Depending on land sink treatment, reported national emissions can shift significantly, with GWPNLS potentially resulting in net-negative totals for countries like Brazil. Together, these metrics enhance consistency across climate accounting frameworks, enabling more accurate integration of land-use dynamics into carbon footprinting, LCAs, national reporting, and climate policy.