Figure 1. Quantifying Climate Policy Curves (CPCs). The relationship between the carbon price per ton of CO2 in 2025, the annual constant growth rate for future carbon prices (2% (red), 4% (green) and 6% (blue)) and the global temperature by 2100 (above the 1850–1900 average). Panel A shows climate uncertainty shaded regions based on ‘likely’ ranges (66% probability) for the equilibrium climate sensitivity between 2.5 and 4°C in the IPCC AR6 report (World Bank Citation2023). Panel B illustrates how the 4%-CPC shifts when alternative policies that are translated into an equivalent carbon price trajectory are implemented either as a substitute for (dashed green line) or a complement to the uniform carbon price (dotted green line). For our illustration we assume that complementary policies increase the emission reduction rate by an arbitrary 20% in each period, while policies that only substitute a uniform carbon price reduce the emission reduction rate by a factor of 20% (see Supplementary Information B for details). Panel C shows a heatmap of global average temperature increase by 2100 for various combinations of initial carbon prices in 2025 and annual carbon price growth rates. The temperature colour scale is shown on the right. Contours that indicate carbon price paths that lead to Paris Agreement temperature goals are denoted by white lines. Panel D shows a comparison of DICE-based CPCs with a CPC fitted to AR6 model simulations. The grey dots represent AR6 data on the 2025 carbon price per ton of CO2 and the global-mean surface air temperature (GSAT), and the black line fits a power function to these data. The green and the blue line are the CPCs based on an updated DICE model with 4% and 6% carbon price growth rates. All prices are in 2022 dollars. See the Supplementary Information for a description of methods.