Are the Observed Changes in Heat Extremes Associated With a Half‐Degree Warming Increment Analogues for Future Projections?

Projecting climate impacts of a half‐degree warming increment is of high priority on post Paris Agreement science agendas. As the real world has already witnessed a 0.5°C global mean surface temperature warming increment, the observed climate changes associated with the half‐degree warming may be analogues for future projections. This hypothesis is examined by comparing the heat extreme changes in China derived from the observational records to projections of the Community Earth System Model (CESM) low‐warming experiment, which is the first short‐term stabilized simulation dedicated for the 1.5 and 2°C warming targets. The results of the CESM historical simulations are also evaluated. From the perspective of spatially aggregated, the heat extreme changes in China under the historical 0.5°C warming are detectable in observations. The nighttime extremes manifest more significant increase than daytime extremes. Heat extreme changes under the past half‐degree warming increment are reasonably captured in the historical simulations with slightly weaker magnitudes. The changes in the intensity indices in observations are better reproduced by the historical simulations than the frequency and duration indices. For the heat extreme changes in the future 0.5°C warming, the observational records can serve as conservative analogues in daytime extremes, while the nighttime extreme indices show comparable or weaker changes. The future reduction of anthropogenic aerosol emissions will amplify the increase of heat extremes in comparison to present day especially during daytime in China. Given the possibly intensified extremes associated with future aerosol reductions, more attention should be paid to the currently heavy polluted regions. Plain Language Summary: Since the Paris Agreement called for limiting the future global warming under 2°C and pursuing efforts to limit under 1.5°C, great efforts have been devoted to exploring the benefits of the 0.5°C less warming on natural and social systems. Since the world has already witnessed a 0.5°C warming increment, whether the associated observed climate changes can be analogues for future projections is an interesting and important question. Focusing on the heat extreme changes over continental China, we revisit the observational data sets to evaluate the performance of the Community Earth System Model (CESM) historical simulations and then compare the observed changes with the CESM 1.5°C/2°C future projections. We find that the heat extreme changes under the past 0.5°C warming increment are detectable in observations and can be well reproduced by the historical simulations. The changes of intensity indices in the observations are better reproduced by the model than the frequency and duration indices. For the daytime heat extremes, the observations only give the lower boundary for the projected changes in future 0.5°C warming. China may experience severer increase in daytime heat extremes due to possible aerosol reductions in the future. Our results would provide useful information to climate change adaption and risk management. Key Points: The increases of the general heat extremes under the past 0.5°C warming increment in the observational records are detectable in ChinaThe CESM historical simulations can reproduce the changes of the heat extremes in China but with slightly weaker magnitudesThe daytime extreme changes in observations can serve as conservative analogues for the future projections [ABSTRACT FROM AUTHOR]