GC037-0005
Evaluating Aerosol Solar Reflection Climate Models by Post Stratospheric Mass Injection Response Observations

Wednesday, 9 December 2020
Poster
Manvendra Krishna Dubey1, Petr Chylek2, Steve Guimond3, Gennaro D'Angelo4 and J M Reisner1, (1)Los Alamos National Laboratory, Los Alamos, NM, United States, (2)Los Alamos Natl Lab, Los Alamos, NM, United States, (3)University of Maryland Baltimore County, Department of Physics and NASA/GSFC, Baltimore, MD, United States, (4)Los Alamos National Laboratory, Theoretical Division, Los Alamos, NM, United States
Abstract:
Climate models are used to assess geoengineering schemes that inject aerosols into the stratosphere reflecting sunlight to cool the earth surface and offset anthropogenic greenhouse warming. The explored aerosols include sulfate, soot and calcium carbonate with distinct optical and microphysical properties. El. Chicon (1982) and Pinatubo (1992) volcanoes lofted large amounts of sulfur dioxide that oxidized to sulfate in the tropical stratosphere and cooled the surface providing historic data useful to evaluate climate models. Furthermore, large stratospheric mass injections of sooty smoke by the 2017 Pyrocumulonimbus British Columbia (BC17) event provide details on processes that control the stratospheric smoke lifetime and burden.

We compare observed hemispherical mean surface temperature (HadCRUT4.6.0.0) and the ensemble means of the CMIP5 climate models' reconstructions (40 models, over 100 simulations) using regressions analysis with observed forcing. We find that volcanic aerosol regression coefficients of the CMIP5 simulations are significantly larger than the volcanic aerosol coefficients of the observed temperature. The largest overestimate is in the winter season of each hemisphere (Chylek GRL 2020). We dig deeper into the post volcanic climate record to show that low latitude cooling is followed by wintertime warming at high latitudes and use it to evaluate individual model performance. Models are able to predict these patterns after Mt Pinatubo eruption but there is a delayed response of surface temperatures after the El Chicon eruption. We rank the models by their skill and recommend such criteria be used for geoengineering assessments. The climate response of aerosol injection is complex and regional, and it needs to be much better understood before it is considered for climate intervention.

We perform global GEOS-5 and CESM simulations of BC17 smoke injection and match observations that imply a smoke lifetime of 4-6 months, using a 2% soot content. We find that larger amounts of soot increase this lifetime by enhancing self-lofting higher into the stratosphere. Dark aerosols like soot or hematite will have longer residence times than white aerosols like calcium carbonate that have been proposed and tested on small scale in the field.

<< Previous Abstract | Next Abstract >>