“[…] varying the SO2 injection area seasonally would result in a similar global mean cooling effect as injecting SO2 to the equator, but with a more uniform zonal distribution of shortwave radiative forcing.” p.1
“Most previous modelling studies have investigated scenarios which inject sulfur along or close to the equator. This choice of injection region is well justified because the equator, on the average, receives the highest levels of solar radiation. In addition, the stratospheric circulation transports particles efficiently from the equator around the global atmosphere (Robock et al., 2008). However it has been found in several studies that preventing greenhouse gas (GHG) induced warming by equatorial injections of sulfur lead to overcooling of the tropics and undercooling of the polar regions, compared to the global mean decrease in temperature (Aswathy et al., 2015; Jones et al., 2010; Jones et al., 2016; McCuster et al., 2012; Yu et al., 2015).” p.2
“However, sulfur injected as SO2 takes weeks to months before it is oxidized and forms large enough particles to reflect solar radiation efficiently. Thus to obtain maximum aerosol forcing, one strategy could be to inject sulfur before the intensity of solar radiation has reached its maximum value at the injection latitude, thus leaving time for oxidation and particle growth.” p.3
“After two years, sulfate particles from the injections are removed from the atmosphere.” p.4
“[…] the lifetime of stratospheric sulfur is longer when injected to the equator (Robock et al., 2008).” p.6
“Previous research has shown that higher injections per unit volume lead to relatively larger particles, which in turn leads to relatively shorter lifetime of particles in the atmosphere (Heckendorn et al., 2009; English et al., 2012; Niemeier et al., 2011).” p.6
“Because SRM is turned on abruptly at full force in 2020, it would lead to a fast cooling. In the real world this kind of action is unlikely but based on the simulations plausible if needed for example prevent climate warming emergency (Kravitz et al., 2011).” p.9
“It has been shown that there is a slow decrease in temperature still decades after a decrease in shortwave radiation (Schaller et al., 2014).” p.10
“After the SRM is suspended in 2070 there is a very fast warming, called the termination effect of geoengineering (Jones et al., 2013). This warming is of the same magnitude as the cooling immediately after the sulfur injection is started. Thus, after the SRM is suspended, the climate remains significantly cooler for decades.” p.10
“Compensating the GHG induced global warming using SRM leads to a reduction in the global mean precipitation (Kravitz et al., 2013b; Ferraro and Griffiths, 2016). This is also supported by our simulations. Immediately after the injection has been started, the global mean precipitation falls clearly under the level of year 2010[…]” p.10
“Precipitation is thus more affected by the SRM than CO2.” p.10
“Aerosol particles both absorb radiation (which is then emitted as LW radiation) and they reduce the SW radiation at surface. These effects lead to a drier climate (Ferraro and Griffiths 2016).” p.11
“It has been also shown that P – E (Precipitation – Evaporations) will become more intense (Seager et al., 2010) which will cause wet areas to become wetter but also drying in the subtropical regions such as Mediterranean, Southern part of Africa and Australia.” p.12
“According our aerosol microphysical simulations by GCM, it would be possible to maintain as large global cooling effect as by injecting sulfur only in the equator while concentrating the cooling effect more to the midlatitudes than tropics. This could be achieved if the sulfur injection area is changed during the year.” p.13
“This highlights the role of feedbacks and ocean temperature which reacts slowly to the radiation changes in the atmosphere.” p.14
30° N – Algeria, Libya, Egypt, Israel, Jordan, Saudi Arabia, Iraq, Kuwait, Persian Gulf, Iran, Afghanistan, Pakistan, India, Nepal, People’s Republic of China, East China Sea, Japan, Pacific Ocean, Mexico, Gulf of California, United States, Gulf of Mexico, Atlantic Ocean, Morocco.
10° N – Togo, Benin, Nigeria, Cameroon, Chad, Central African Republic, Sudan, South Sudan, Abyei, Ethiopia, Somalia, Indian Ocean, India, Myanmar (Burma), Thailand, Gulf of Thailand, Vietnam, South China Sea, Philippines, Sulu Sea, Tañon Strait, Cebu Strait, Bohol Sea, Surigao Strait, Dinagat Sound, Pacific Ocean, Federated States of Micronesia, Marshall Islands, Costa Rica, Caribbean Sea, Colombia, Venezuela, Atlantic Ocean, Guinea, Guinea / Sierra Leone border, Ivory Coast, Burkina Faso, Ghana.
10° S – Atlantic Ocean, Angola, Democratic Republic of the Congo, Zambia, Malawi, Lake Malawi, Tanzania, Indian Ocean, Indonesia, Savu Sea, Timor Sea, Arafura Sea, Coral Sea, Papua New Guinea, Solomon Sea, Pacific Ocean, Cook Islands, Kiribati, French Polynesia, Peru, Brazil, Bolivia.
30° S – South Africa, Lesotho, South Africa, Indian Ocean, Australia, Pacific Ocean, Chile, Argentina, Brazil, Atlantic Ocean.