The Multi-Decadal Response to Net Zero CO₂ Emissions and Implications for Emissions Policy

How confident are we that CO₂ emissions must reach net zero or below to halt CO₂-induced warming? The IPCC's sixth assessment report concluded that “limiting human-induced global warming to a specific level requires … reaching at least net zero CO₂ emissions.” This is much stronger language than the special report on the global warming of 1.5°C, which concluded that reaching net zero CO₂ emissions would be sufficient. Here we show that “approximately net zero” is better supported than “at least net zero.” We estimate the rate of adjustment to zero emissions (RAZE) parameter (−0.24 to +0.17%/yr), defined as the fractional change in CO₂-induced warming after CO₂ emissions cease. The RAZE determines the CO₂ emissions compatible with halting warming over multiple decades: in 1.5°C-consistent scenarios, CO₂ emissions consistent with halting anthropogenic warming are +2.2 GtCO₂/yr (5–95th percentile range spans −7.3 to +6.2 GtCO₂/yr), similar to the expected emissions from unmodelled Earth system feedbacks.