Journal Article
Atmospheric Chemistry and Physics, vol. 18, iss. 14, pp. 10133-10156, 2018
Authors
Duoying Ji, Songsong Fang, Charles L. Curry, Hiroki Kashimura, Shingo Watanabe, Jason N. S. Cole, Andrew Lenton, Helene Muri, Ben Kravitz, John C. Moore
Abstract
Abstract. We examine extreme temperature and precipitation under two
potential geoengineering methods forming part of the Geoengineering Model
Intercomparison Project (GeoMIP). The solar dimming experiment G1 is designed
to completely offset the global mean radiative forcing due to a
CO2-quadrupling experiment (abrupt4 × CO2), while in
GeoMIP experiment G4, the radiative forcing due to the representative
concentration pathway 4.5 (RCP4.5) scenario is partly offset by a simulated
layer of aerosols in the stratosphere. Both G1 and G4 geoengineering
simulations lead to lower minimum temperatures (TNn) at higher latitudes and
on land, primarily through feedback effects involving high-latitude processes
such as snow cover, sea ice and soil moisture. There is larger cooling of TNn
and maximum temperatures (TXx) over land compared with oceans, and the
land–sea cooling contrast is larger for TXx than TNn. Maximum 5-day
precipitation (Rx5day) increases over subtropical oceans, whereas warm spells
(WSDI) decrease markedly in the tropics, and the number of consecutive dry
days (CDDs) decreases in most deserts. The precipitation during the tropical
cyclone (hurricane) seasons becomes less intense, whilst the remainder of the
year becomes wetter. Stratospheric aerosol injection is more effective than
solar dimming in moderating extreme precipitation (and flooding). Despite the
magnitude of the radiative forcing applied in G1 being ∼ 7.7 times
larger than in G4 and despite differences in the aerosol chemistry and
transport schemes amongst the models, the two types of geoengineering show
similar spatial patterns in normalized differences in extreme temperatures
changes. Large differences mainly occur at northern high latitudes, where
stratospheric aerosol injection more effectively reduces TNn and TXx. While
the pattern of normalized differences in extreme precipitation is more
complex than that of extreme temperatures, generally stratospheric aerosol
injection is more effective in reducing tropical Rx5day, while solar dimming
is more effective over extra-tropical regions.
