Global warming mitigation by sulphur loading in the stratosphere: dependence of required emissions on allowable residual warming rate amg

An appr­oach to miti­gate global warming via sulphur loading in the stra­tosp­here (geoe­ngin­eer­ing) is studied, empl­oying a large ense­mble of nume­rical expe­rime­nts with the climate model of inte­rmed­iate comp­lex­ity IAP RAS CM. The model is forced by the hist­ori­cal+SRES A1B anth­ropo­genic gree­nho­use gases+trop­osph­eric sulp­hates scen­ario for 1860–2100 with addi­tio­nal sulphur emis­sions in the stra­tosp­here in the twenty-first century. Diff­erent ense­mble members are cons­truc­ted by varying values of the para­met­ers gove­rning mass, hori­zon­tal dist­ribu­tion and radi­ative forcing of the stra­tosp­heric sulp­hates. It is obta­ined that, given a global loading of the sulp­hates in the stra­tosp­here, among those studied in this paper lati­tudi­nal dist­ribu­tions of geoe­ngin­eer­ing aero­sols, the most effi­cient one at the global basis is that peaked between 50◦ N and 70◦ N and with a some­what smaller bur- den in the tropics. Uniform lati­tudi­nal dist­ribu­tion of stra­tosp­heric sulp­hates is a little less effi­cient. Sulphur emis­sions in the stra­tosp­here requ­ired to stop the global temp­erat­ure at the level corr­espo­nding to the mean value for 2000–2010 amount to more than 10 TgS/year in the year 2100. These emis­sions may be reduced if some warming is allowed to occur in the twenty-first century. For inst­ance, if the global temp­erat­ure trend Sg in every decade of this century is limited not to exceed 0.10 K/decade (0.15 K/decade), geoe­ngin­eer­ing emis­sions of 4–14 TgS/year (2–7 TgS/year) would be suff­ici­ent. Even if the global warming is stopped, temp­erat­ure changes in diff­erent regions still occur with a magn­itude up to 1 K. Their hori­zon­tal pattern depends on implied lati­tudi­nal dist­ribu­tion of stra­tosp­heric sulp­hates. In addi­tion, for the stab­ili­sed global mean sur- face air temp­erat­ure, global prec­ipit­ation decr­eases by about 10%. If geoe­ngin­eer­ing emis­sions are stopped after several decades of impl­emen­tat­ion, their clim­atic effect is removed within a few decades. In this pe- riod, surface air temp­erat­ure may grow with a rate of several Kelvins per decade. The results obta­ined with the IAP RAS CM are further inte­rpre­ted empl­oying a glob­ally aver­aged energy–balance climate model. With the latter model, an anal­yti­cal esti­mate for sulp­hate aerosol emis­sions in the stra­tosp­here requ­ired climate miti­gat­ion is obta­ined. It is shown that effe­ctive vert­ical loca­lisa­tion of the imposed radi­ative forcing is impo­rtant for geoe­ngin­eer­ing effi­cie­ncy.