The figure on the right shows simulated changes in global mean 2m temperature for the period 1850-2100 relative to the reference period 1995-2014. Simulations at DKRZ were carried out with the two different MPI-ESM configurations LR and HR and with AWI-CM for the SSP scenarios (SSP126, SSP245, SSP370 und SSP585). Depending on the combination of experiment and model, simulations were run up to ten times with slightly changed initial conditions (an ensemble with up to ten realizations) in order to capture the uncertainty due to internal climate variability. The range of temperature changes resulting from the different scenarios is due to the uncertainty of future socioeconomic and technological developments until the end of the century. Another uncertain factor is the still insufficiently known climate sensitivity of Earth (equilibrium change in annual global mean surface temperature in reaction to a doubling of the CO2 equivalent concentrations in the atmosphere), which may differ from model to model. Especially the purple graphs show that the warming at strongly increasing greenhouse gas levels (SSP585) computed with the model AWI-CM is more intense than with both versions of MPI-ESM.
The historical period of 1850-2014 was simulated as a 10-member ensemble using MPI-ESM both in LR and HR resolution, and as a 5-member ensemble using AWI-CM. The MPI-ESM LR simulations of the four SSPs were likewise carried out as 10-member ensembles, while for MPI-ESM HR, only one realization was performed for SSP126 and SSP585 respectively, two realizations for SSP245 and ten for SSP370. With AWI-CM, a single realization was computed for SSP scenarios SSP126, SSP245 and SSP585. For SSP370, however, a 5-member ensemble was computed.
The thick yellow line represents the observed evolution of the global mean change in 2m temperature from 1851 to 2020 on the basis of HadCRUT4, a dataset developed at the University of East Anglia. Moreover, a dashed black line indicates the two-degree target (“not more than two degrees of warming until the end of the century compared to the preindustrial state”) and the 1.5-degree target. According to the simulations of SSP126 with MPI-ESM shown here, it would still be possible to reach the 1.5-degree target, while AWI-CM simulates a warming that already exceeds this target.