Exploring the asymmetry and rate of SAT warming over the global land area under the 1.5 °C and 2 °C climate change targets

The Paris Agreement establishes targets for the increase in global mean temperature of 1.5 °C and 2 °C, relative to pre-industrial levels. Recent studies suggest that the climate change impacts of these two goals are markedly different, and the additional 0.5 °C increase in the global mean surface air temperature (SAT) may lead to drastic, non-linear increases in the extreme and average temperatures of most regions. In this study, we use model results from the Coupled Model Intercomparison Project 5 (CMIP5) to illustrate the asymmetric nature of the warming trends that will result over the global land area under these two climate change targets. The results show that the SAT increase reaches 1.5 °C by 2040 (2040 ± 6), considering RCP2.6 to RCP8.5, whereas the SAT increase reaches 2.0 °C by 2060 (2060 ± 12), considering RCP4.5 to RCP8.5. The SAT increase over land is meridionally and zonally asymmetric, especially in the Northern Hemisphere. What’s global warming and rising concentrations of emissions will exacerbate the asymmetric warming from north to south especially over land. In addition to the longitudinal changes, the magnitude of the SAT increase at higher latitudes is significantly greater than that of comparable areas at middle to low latitudes. Additionally, the time of the SAT increase over the high-latitude land areas occurs much earlier than elsewhere. In addition, the difference in the timing of this onset in the longitudinal direction is substantial, but the difference in the zonal direction is small. Furthermore, the SAT increase over most of the global land area reaches 1.5 °C before the middle of twenty-first century and reaches 2.0 °C before 2070. In addition, over 20% of the global land area, the SAT increase reaches 1.5 °C before 2006, whereas almost none of the land area exhibits a change of 2.0 °C before 2006.