Changes in extremely hot days under stabilized 1.5 and 2.0 °C global warming scenarios as simulated by the HAPPI multi-model ensemble

Abstract

Abstract. The half a degree additional warming, prognosis and projected impacts (HAPPI) experimental protocol provides a multi-model database to compare the effects of stabilizing anthropogenic global warming of 1.5 • C over preindustrial levels to 2.0 • C over these levels. The HAPPI experiment is based upon large ensembles of global atmospheric models forced by sea surface temperature and sea ice concentrations plausible for these stabilization levels. This paper examines changes in extremes of high temperatures averaged over three consecutive days. Changes in this measure of extreme temperature are also compared to changes in hot season temperatures. We find that over land this measure of extreme high temperature increases from about 0.5 to 1.5 • C over present-day values in the 1.5 • C stabilization scenario, depending on location and model. We further find an additional 0.25 to 1.0 • C increase in extreme high temperatures over land in the 2.0 • C stabilization scenario. Results from the HAPPI models are consistent with similar results from the one available fully coupled climate model. However, a complicating factor in interpreting extreme temperature changes across the HAPPI models is their diversity of aerosol forcing changes.

Global warming from 1.5 to 2 °C will lead to increase in precipitation intensity in China

“…This means that the projection of extreme precipitation is not applicable to a stabilized climate scenario. The HAPPI (Half a degree of Additional warming, Prognosis and Projected Impacts) project has conducted a series of experiments for recent observations and 1.5 and 2 C warmer worlds, and the results are freely available Wehner et al, 2017). Therefore, future work will improve the projection of extreme precipitation events under global warming of 1.5 and 2 C by combining simulation results with those of the HAPPI project.…”

Changes in tropical cyclones under stabilized 1.5 and 2.0 °C global warming scenarios as simulated by the Community Atmospheric Model under the HAPPI protocols

“…With warmer temperatures, conditions that can sustain tropical storm wind speeds extend poleward. Although not considered here, there is potential for an anthropogenic influence on the transition to extratropical characteristics of storms that undergo them (Liu et al, 2017;Zarzycki et al, 2017). In the Southern Hemisphere, Fig.…”

“…However, it does not isolate all of the effects of forcing changes required to stabilize the climate from the present day conditions. In particular, the effect of sulfate aerosol reductions in the atmosphere has a nonlocal effect in the HAPPI simulations and has been demonstrated to be important to assessing changes in tropical cyclones (Huff et al, 2017) and heat waves (Wehner et al, 2017b). As the radiative forcing changes due to CO 2 between the historical and 1.5 • C scenarios may be smaller than the forcing changes due to aerosols, the CO 2 effects in tropical storms may be comparable or even smaller due to the aerosol effects at this stabilization level.…”

Internal variability in European summer temperatures at 1.5 °C and 2 °C of global warming

“…For this purpose, we use a state-of-the-art tool to sample internal variability: the 100-member Max Planck Institute Earth System Model (MPI-ESM) Grand Ensemble (Bittner et Summer monthly mean and daily maximum temperatures at 2 • C of global warming are projected to become around 1 • C higher over Europe than at 1.5 • C of warming (Schleussner et al 2016, Perkins-Kirkpatrick and Gibson 2017, King and Karoly 2017. Sanderson et al (2017) and Wehner et al (2017) also find differences of around 1 • C between 20 year return levels of maximum temperatures at 1.5 • C versus at 2 • C of global warming. These studies are based on climate modelling experiments of different nature: the Coupled Model Intercomparison Project phase 5 (CMIP5) multi-model ensemble (Schleussner et al 2016, Perkins-Kirkpatrick and Gibson 2017, King and Karoly 2017, and ensemble-experiments such as the Half a Degree Additional warming, Prognosis and Projected Impacts project (HAPPI; Mitchell et al 2017) atmosphere-only runs (Wehner et al 2017), and the Community Climate ten-member CESM1 ensemble .…”