Shortened Duration of Global Warming Slowdowns with Elevated Greenhouse Gas Emissions
By analyzing observed and model-simulated data, we investigate how the duration of these episodes will change with different strengths of GHG and aerosol forcing. We found that the duration of warming slowdowns can be more than 30 yr with a slower rate of anthropogenic emissions but would shorten to about 5 yr with a higher one. This duration reduction depends on both the magnitude of the climate response to anthropogenic forcing and the strength of the internal variability. Moreover, the warming slowdowns can still occur even towards the end of this century under high emissions scenarios but with significantly shortened duration.
By analyzing observations and model simulation, this study shows a reduced impact of the internal variability on the global mean surface air temperature changes as the anthropogenic forcing becomes stronger and stronger in the future. As a result, the duration of global warming slowdown as shown in the late 1990s to 2015 and in the 1940s-1970s will be greatly reduced. This will give some guidance on predicting the future climate change on a decadal timescale.
In summary, we evaluated the potential changes of warming slowdown durations for the climate of the past century and a half as well as the climate from now to the end of the 21st century. We found that the duration of warming slowdowns would decrease as anthropogenic forcing increases. This reduction depends on the magnitude of the CO2ea changes for different emissions scenarios and the strength of the internal variability. Under the high emissions scenarios, warming slowdowns could still occur even towards the end of the 21st century, though with shorter durations. The internally generated climate variability such as PDV and AMV can cause the occurrence of warming slowdowns, but it is noticeable that they can also result in the warming speedup when the warming slowdowns end. It is worth pointing out that the global mean aerosol effect on ERF was considered when we built the CO2ea time series. However, the regional heterogeneous distribution of the anthropogenic aerosols is neglected due to the difficulties in deriving the aerosol optical depth from the observed and projected time periods. Although the heterogeneous anthropogenic aerosols will lead to distinct duration changes on regional scales, the effect of this on the estimations for the GMST is expected to be small.