Effects of Different Stratospheric SO₂ Injection Altitudes on Stratospheric Chemistry and Dynamics

Abstract

Strategically applied geoengineering is proposed to reduce some of the known side effects of stratospheric aerosol modifications. Specific climate goals could be reached depending on design choices of stratospheric sulfur injections by latitude, altitude, and magnitude. Here we explore in detail the stratospheric chemical and dynamical responses to injections at different altitudes using a fully coupled Earth System Model. Two different scenarios are explored that produce approximately the same global cooling of 2°C over the period 2042–2049, a high‐altitude injection case using 24 Tg SO2/year at 30 hPa (≈25‐km altitude) and a low‐altitude injection case using 32 Tg SO2/year injections at 70 hPa (between 19‐ and 20‐km altitude), with annual injections divided equally between 15°N and 15°S. Both cases result in a warming of the lower tropical stratosphere up to 10 and 15°C for the high‐ and low‐altitude injection case and in substantial increases of stratospheric water vapor of up to 2 and 4 ppm, respectively, compared to no geoengineering conditions. Polar column ozone in the Northern Hemisphere is reduced by up to 18% in March for the high‐altitude injection case and up to 8% for the low‐altitude injection case. However, for winter middle and high northern latitudes, low‐altitude injections result in greater column ozone values than without geoengineering. These changes are mostly driven by dynamics and advection. Antarctic column ozone in 2042–2049 does not recover from present‐day (2002–2009) values for both cases.

CESM1(WACCM) Stratospheric Aerosol Geoengineering Large Ensemble Project

“…Aerosol size and sedimentation are increased with the injection amount and the efficiency of the sulfates to affect the top of the atmosphere radiative imbalance is reduced (Niemeier and Timmreck 2015;Kleinschmitt et al 2017). The warming of the tropical stratosphere in response to the enhanced aerosol burden results in circulation changes in the stratosphere with potential effects on the quasi-biennial oscillation (QBO; Aquila et al 2014), as well as impacts on the tropospheric circulation (Richter et al 2018). Changes in the chemical composition, including changes in water vapor and ozone, as well as changes in tropospheric clouds, may alter the long-and shortwave climate forcing.…”

“…NOVEMBER 2018 AMERICAN METEOROLOGICAL SOCIETY | on the quasi-biennial oscillation (QBO; Aquila et al 2014), as well as impacts on the tropospheric circulation (Richter et al 2018). Changes in the chemical composition, including changes in water vapor and ozone, as well as changes in tropospheric clouds, may alter the long-and shortwave climate forcing.…”

“…Despite the stabilization of global surface temperature, these simulations show significant changes in atmospheric conditions with global solar reductions or stratospheric sulfur or aerosol injections. Side effects in these simulations include "overcooling" of the tropics and "undercooling" of the poles, leading to continued Arctic summer sea ice loss (e.g., Moore et al 2014;Tilmes et al 2016). Additionally, the slowing of the hydrological cycle (e.g., Schmidt et al 2012) and the potentially uneven cooling between the two hemispheres resulting from solar geoengineering can lead to shifts in precipitation patterns (Haywood et al 2013; Jones et al 2017) and reductions in monsoon precipitation (Tilmes et al 2013).…”

“…NOVEMBER 2018 | and dynamics (Richter et al 2018;Tilmes et al 2018). Stratospheric SO 2 injections in the geoengineering simulation lead to the formation of sulfate aerosols with a maximum burden around the primary injection locations (Fig.…”

“…NOVEMBER 2018 AMERICAN METEOROLOGICAL SOCIETY | for this, we use a feedback algorithm that annually adjusts the injection rates at each of the four locations in response to simulated deviations from the temperature targets based on a weighted contribution of deviations in both the preceding year and integrated through the simulation to that date [for details, see MacMartin et al (2014) and Kravitz et al (2016]. This algorithm aims toward maintaining the target values of T0, T1, and T2 over time.…”