Fig. 3: GHG emissions and the resulting warming effects produced from AC use.

a Total GHG emissions across five SSP-RCP scenarios. The lines represent the GHG emissions based on mean CDD, while the shadows represent possible ranges of GHG emissions based on min and max CDD. b Total GHG emissions in 2050 by fuel and emitter. Total GHG emissions associated with AC use are categorized into four emission sources across two building types: residential and commercial. In residential buildings, CO₂ emissions from AC use comprise ~0.6% from natural gas consumption by gas-powered ACs and 99.4% from electricity consumption. In commercial buildings, CO₂ emissions account for about 0.5% from natural gas consumption and 99.5% from electricity consumption. Non-CO₂ emissions from AC use are from two sources: refrigerant leaks from AC use and other non-CO₂ emissions from power transmission. Regarding the types of AC refrigerants, the default settings of GCAM account for traditional refrigerants, such as HFC-134a and HFC-143a, as well as the low-GWP refrigerant HFC-32. Non-CO₂ emissions from residential and commercial AC use are primarily derived from AC refrigerants (~98.9%), with a minor contribution from power transmission (approximately 1.1%). c Global cumulative GHG emissions and the associated warming effects across scenarios. Triangles in the figure represent the reference warming temperatures for each SSP-RCP scenario, with the dots indicating the additional warming effects caused by the average GHG emissions resulting from AC use. Owing to rounding, the warming contributions for SSP245 and SSP370 appear similar; in fact, the SSP370 value (0.048 °C) is slightly higher than that for the SSP245 scenario (0.045 °C). The error bars denote the range of temperature increases based on the range of global cooling demand under five climate scenarios.