Household consumption is a major driver of global carbon and air-pollutant emissions. As living standards rise, everyday routines become entrenched and reduce the responsiveness of demand to mitigation policies. Consumption-based accounting has traced these burdens through supply chains, yet the scale of emissions that remain locked in by behavioral inertia has stayed poorly quantified. Here we show that locked-in emissions of carbon and air pollutants account for nearly 84% of total household-driven emissions of CO₂, PM_2.5, NO_x, and SO₂ across China, far exceeding the contribution of net consumption growth. Food exhibits the highest locked-in share (approximately 97%), followed by residential expenditure (84–86%). Per-capita habit-locked emissions peak in East and North China, with 32–53% of these emissions originating in the production systems of Nei Mongol and Shandong. Scenario analysis to 2035 reveals that under business-as-usual scenario, habit-locked CO₂ emissions peak around 2030, while habit-locked air-pollutant emissions decline, whereas the deepest and most balanced reductions, 1285 Mt CO₂ together with 218 kt PM_2.5, 729 kt SO₂, and 126 kt NO_x, occur only when carbon-neutrality-oriented policies are paired with attenuated consumption inertia. These findings demonstrate that efficient demand-side synergistic mitigation in China requires systematic substitution of habit-locked carbon and air-pollutant emissions with lower-emission, affordable alternatives.

Cities play a pivotal role in global decarbonization, acting as a critical driver of carbon emissions. Accurately allocating carbon mitigation responsibility (CMR) is essential for designing effective and equitable climate policies. How cities manage carbon leakage across boundaries through supply chains and implement plan of increasing forest carbon sinks are important components for designing a fair and inclusive CMR. However, the combined impact of trade-related carbon leakage and forest carbon sinks on CMR allocation remains poorly understood. Here, we develop an integrated CMR allocation framework that accounts for both carbon leakage and variation of forest carbon offsets. When applied to the cities within the Guangdong–Hong Kong–Macao Greater Bay Area in China, it becomes evident that the inclusion of carbon leakage results in substantial alterations in mitigation quotas. Adjustments are observed to vary between ±10% and 50% across these cities from 2005 to 2020, a trend that is anticipated to continue until 2035. The redistribution of outsourced emissions through supply chains alleviates the mitigation burden on producer cities by 20–30%. Additionally, accounting for carbon sinks substantially influences CMR allocation, particularly in forest-rich cities, which may see their carbon budgets increase by up to 10%. Under an enhanced climate policy scenario, the growth rate of total mitigation quotas from 2025 to 2035 is projected to decrease by 40% compared to a business-as-usual trajectory, reducing the burden on major producer cities. Our proposed CMR framework provides a robust basis for incentivizing coordinated mitigation efforts, promoting decarbonization in supply chains and enhancement of urban carbon sink capacities.