Can Global Mean Temperatures be Held to 1.5°C or Less without Major Efforts in Carbon Removal/Geoengineering?

Abstract

The 2015 international Paris Agreement called for pursuing efforts to limit the changes in climate to 1.5°C above pre-industrial levels. This study uses two approaches to re-examine this feasibility more fully. The observed trends in the temperature record provide one means to estimate when 1.5°C will be reached. Examination of the remaining allowed carbon emissions provides another approach. The temperature record and the observed trends in temperature over recent decades suggest that 1.5°C will be reached by 2032–2042. Consideration of the equivalent amount of CO2 reveals the ranges of 266, 366 and 531 GtCO2-eq still allowed for 67%, 50% and 33% probabilities, respectively, of staying within the temperature limit. At the current rate of emissions, the 50% limit would be reached in eight years. If an emissions reduction of 4% per year beginning in January 2023 is considered, the 67% likelihood for staying within the 1.5°C limit is passed in 2030 and the 50% likelihood is passed in 2035. As a result, humanity is very unlikely to meet the identified targets needed to keep the global temperature change to 1.5°C and the SSP1-1.9 scenario assumptions for future emissions toward enabling a limit of 1.5°C are also extremely unlikely.