PNNL

Abstract

Strategic geoengineering has been 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 state-of-the-art climate model. Two different sce-narios are explored that produce approximately the same global cooling of 2?C over the period 2042 – 49, a high altitude injection case using 24 Tg SO2 yr-1 at 30 hPa (˜ 25km altitude), and a low altitude injection case using 32 Tg SO2 yr-1 injections at 70 hPa (˜ 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 increase of water vapor of 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 mid- and high northern latitudes, low altitude injections result in column ozone greater than without geoengineering. These changes are mostly driven by dynamics and advection. Antarctic column ozone in 2040-49 does not recover from present day values for both cases.