Data set for the study "Combined uncertainties in climate and carbon-cycle feedbacks could allow for future warming much higher than expected"

In light of uncertainties regarding climate sensitivity and future anthropogenic greenhouse gas emissions, we explore the plausibility of global warming over the next millennium which is significantly higher than what is expected. While progress in decarbonizing the global economy has already resulted in global anthropogenic emission significantly deviating from the most extreme emission scenarios (SSP3-7.0 and SSP5-8.5), intermediate emission scenarios are still plausible. Significant warming in these scenarios still cannot be ruled out as uncertainties in equilibrium climate sensitivity (ECS) remain very large. Furthermore, important carbon-cycle feedbacks are frequently omitted from models employed in climate change projections, highlighting the need to re-evaluate the range of uncertainties under realistic emission scenarios. Using an Earth system model with interactive CO2 and CH4, we performed simulations for the next millennium under extended SSP1-2.6, SSP4-3.4 and SSP2-4.5 scenarios. These scenarios are usually associated with peak global warming levels of 1.5, 2 and 3°C, respectively, for an ECS of ∼3°C, considered the best estimate in the latest IPCC report. As ECS values significantly lower or higher than this estimate cannot be ruled out, we represent a wide range of ECS from 2 to 5°C, defined as the ”very likely” range by the IPCC. Our results show that achieving the Paris Agreement goal of a 1.5°C temperature increase is only feasible if ECS is lower than the current best estimate of 3°C. With an ECS of 5°C, peak warming in all considered scenarios more than doubles compared to an ECS of 3°C. Approximately 50% of this additional warming is attributed to positive climate–carbon cycle feedbacks with comparable contributions from CO2 and CH4. The interplay between potentially high ECS and carbon cycle feedbacks could drastically enhance future warming, demonstrating the importance of properly accounting for all major climate feedbacks and associated uncertainties in projecting future climate change.