Indices of extremes: geographic patterns of change in extremes and associated vegetation impacts under climate intervention

Abstract

Abstract. Extreme weather events have been demonstrated to be increasing in frequency and intensity across the globe and are anticipated to increase further with projected changes in climate. Solar climate intervention strategies, specifically stratospheric aerosol injection (SAI), have the potential to minimize some of the impacts of a changing climate while more robust reductions in greenhouse gas emissions take effect. However, to date little attention has been paid to the possible responses of extreme weather and climate events under climate intervention scenarios. We present an analysis of 16 extreme surface temperature and precipitation indices, as well as associated vegetation responses, applied to the Geoengineering Large Ensemble (GLENS). GLENS is an ensemble of simulations performed with the Community Earth System Model (CESM1) wherein SAI is simulated to offset the warming produced by a high-emission scenario throughout the 21st century, maintaining surface temperatures at 2020 levels. GLENS is generally successful at maintaining global mean temperature near 2020 levels; however, it does not completely offset some of the projected warming in northern latitudes. Some regions are also projected to cool substantially in comparison to the present day, with the greatest decreases in daytime temperatures. The differential warming–cooling also translates to fewer very hot days but more very hot nights during the summer and fewer very cold days or nights compared to the current day. Extreme precipitation patterns, for the most part, are projected to reduce in intensity in areas that are wet in the current climate and increase in intensity in dry areas. We also find that the distribution of daily precipitation becomes more consistent with more days with light rain and fewer very intense events than currently occur. In many regions there is a reduction in the persistence of long dry and wet spells compared to present day. However, asymmetry in the night and day temperatures, together with changes in cloud cover and vegetative responses, could exacerbate drying in regions that are already sensitive to drought. Overall, our results suggest that while SAI may ameliorate some of the extreme weather hazards produced by global warming, it would also present some significant differences in the distribution of climate extremes compared to the present day.

Detecting Changes in Global Extremes Under the GLENS‐SAI Climate Intervention Strategy

“…The main focus of this study is on extreme temperature and precipitation over land (e.g., Tye et al., 2022). Two indices are analyzed (Figure 1): warm days (TX90p) and wet‐day precipitation (R95pTOT).…”

Opinion: The Scientific and Community-Building Roles of the Geoengineering Model Intercomparison Project (GeoMIP) - Past, Present, and Future

“…In our context, as explained for instance by Hawkins and Sutton (2009), it can come from internal variability, uncertainty in the climate response, scenario uncertainty, and parametric or structural uncertainty. Internal variability can be better studied in the context of large ensembles of simulations with single models, of which some are available for geoengineering studies already (Tilmes et al, 2018;Richter et al, 2022)): the use of multiple realizations from very similar initial conditions allows for a better separation of a given forcing signal from noise derived from the inherent chaoticity of the atmospheric and oceanic system, and makes exploring the timing of the emergence of such a signal easier Tye et al, 2022). GeoMIP is suited to explore uncertainties in the climate response as it allows an exploration of structural differences between models to a standardized forcing, but it does not directly address single-model uncertainty based on specific parameters in the physical representation of various aspects of the climate system: for such an endeavor, perturbed-physics ensembles within a single model may offer a much clearer answer.…”

“…GLENS focused on producing a large ensemble (20 members) of simulations using one model (CESM1(WACCM)) and one, at the time, novel strategy (using an automated feedback loop capable of determining where and how much SO 2 injections should go in the next year). This allowed for a more thorough exploration of, for instance, signal-to-noise emergence and extreme events (Aswathy et al, 2015;Pinto et al, 2020;Tye et al, 2022). Both GeoMIP and GLENS have enabled numerous studies through the DEGREES Initiative, enabling developing countries to assess changes they may experience under geoengineering.…”

Assessing Responses and Impacts of Solar climate intervention on the Earth system with stratospheric aerosol injection (ARISE-SAI): protocol and initial results from the first simulations

“…Other modeling centers should consider providing this (model specific) information as well. In addition, higher-frequency (daily averaged, 3-hourly averaged, 3-hourly instantaneous, and 1hourly mean) output is desired for the atmospheric model that will enable analysis of extreme events (e.g., Tye et al, 2022). The atmospheric output at various time frequencies is described in Appendix A in Tables A2-A5.…”

“…b Variables that are available (but erroneous) in the first five members of CESM2(WACCM6) SSP2-4.5 simulations. Variables in bold are used to calculate indices of extremes such as those presented inTye et al (2022).…”