Simulated Effects Of Solar Geoengineering On Ocean Acidification

Since the industrial revolution,human activities have caused a lot of CO2 emissions and made CO2 concentration continue to rise,leading to global warming.Meanwhile,the ocean absorbs CO2,which induces acidification,posing a threat to marine organism.In recent years,scientists have proposed solar radiation management(SRM)as an alternative way to tackle global warming,which cools the earth by reducing the solar radiation reaching the atmosphere and the earth surface.Currently,the study of solar geoengineering is focused more on climate but less on ocean acidification.This study simulates the effects of solar geoengineering on ocean acidification,which helps to fully evaluate the effects of geoengineering on global climate and environment.In this study,we use University of Victoria Earth System Climate Model(UVic ESCM)to simulate and analyze the effects of implementing solar geoengineering with CO2 increasing on physical climate and ocean acidification.The environmental factors studied here include dissolved inorganic carbon(DIC),alkalinity,temperature and salinity,and parameters of ocean acidification include pH and aragonite(a metastable form of calcium carbonate)saturation state(O).This study uses Representative Concentration Pathways 8.5(RCP8.5)scenario to simulate the increase of atmospheric CO2.The simulation results show that under RCP8.5 scenario,the total ocean CO2 uptake from the year 1800 to 2100 amounts to 547 PgC.Relative to pre-industrial level,by the year 2100,sea surface DIC will increase by 181 ?mol kg-1,alkalinity will decrease by 13 ?mol kg-1 and temperature will increase by 2.8?,but salinity won't change significantly.Under this background,by the year 2100,relative to pre-industrial level,global mean sea surface pH will decrease by 0.43 and ? will decrease by 1.77.Under RCP8.5 scenario,solar geoengineering is implemented from the year 2020 to cool the ocean surface to its pre-industrial level,which induces an increase of 37 PgC in ocean CO2 uptake by the year 2100 as a result of solubility increase in CO2.Relative to RCP8.5 scenario,by the year 2100,sea surface temperature will decrease by 2.8? under the geoengineering scenario,the decrease of which will affect the ionization constant of carbonic acid to make pH decrease but ?increase;meanwhile,DIC will increase 24 ?mol kg-1 and alkalinity will increase 9 ?mol kg-1.The changes of DIC and alkalinity will affect the ionization equilibrium of carbonic acid and consequently change the concentration of hydrogen ion and carbonate to affect pH and ?,The increase of DIC will decrease pH and Cl while the increase of alkalinity will increase pH and ?.The change of salinity under the geoengineering scenario is relatively small,and thus has little effect on ocean acidification.Generally,relative to CO2 increasing scenario,solar geoengineering will make pH nearly constant,but decrease 0 by 0.16 by affecting environmental factors.The quantitative analysis results show that the effect of the change of DIC on pH is counteracted by the effects of the changes of alkalinity and temperature on pH.Meanwhile,? is on the decrease mainly due to the increase of DIC.Besides,the linear addition of the effects of environmental factors like DIC,alkalinity,temperature and salinity on ocean acidification is nearly equal to the effects of the simultaneous changes of those environmental factors.Ocean acidification will threaten the living eonditions of coral reefs by decreasing seawater?,the low state of which i5 detrimental to formation of the skeleton of eoral reefs.And the implement of solar geoengineering will decrease seawater Q further.Under RCP8.5 scenario,95%of the shallow-water coral reefs located in seawater with ?>3.5 in pre-industrial time while the percentage will decrease to zero by the year 2100;91%of the cold-water coral reefs located in seawater with ?>1 in pre-industrial time while the percentage will decrease to 55%by the year 2100.Relative to RCP8.5 scenario,the percentage of the shallow-water coral reefs will decrease to zero 10 years earlier under the geoengineering scenario,and the percentage of the cold-water coral reefs in the seawater with ?>1 will decrease to 34%.On the whole,ocean acidification under CO2 increasing scenario is affected by both the increase of CO2 concentration and ocean warling.Our simulation shows that solar geoengineering can effectively mitigate global wanning but fails to alleviate ocean acidification.Therefore,it should be careful to consider the implement of solar geoengineering in reality.