This study estimates direct radiative forcing by tropospheric ozone and all aerosols between the years 1850 and 2000,using the new IPCC AR5 (the Intergov-ernmental Panel on Climate Change Fifth Assessment Report) emissions inventories and a fully coupled chem-istry-aerosol general circulation model.As compared to the previous Global Emissions Inventory Activity (GEIA) data,that have been commonly used for forcing estimates since 1990,the IPCC AR5 emissions inventories report lower anthropogenic emissions of organic carbon and black carbon aerosols and higher sulfur and NO x emis-sions.The simulated global and annual mean burdens of sulfate,nitrate,black carbon (BC),primary organic aero-sol (POA),secondary organic aerosol (SOA),and ozone were 0.79,0.35,0.05,0.49,0.34,and 269 Tg,respectively,in the year 1850,and 1.90,0.90,0.11,0.71,0.32,and 377 Tg,respectively,in the year 2000.The estimated annual mean top of the atmosphere (TOA) direct radiative forc-ing of all anthropogenic aerosols based on the AR5 emis-sions inventories is-0.60 W m-2 on a global mean basis from 1850 to 2000.However,this is-2.40 W m-2 when forcing values are averaged over eastern China (18-45°N and 95-125°E).The value for tropospheric ozone is 0.17 W m-2 on a global mean basis and 0.24 W m-2 over east-ern China.Forcing values indicate that the climatic effect of aerosols over eastern China is much more significant than the globally averaged effect.
A unified chemistry-aerosol-climate model is applied in this work to compare climate responses to chang- ing concentrations of long-lived greenhouse gases(GHGs,CO2,CH4,N2O),tropospheric O3,and aerosols during the years 1951–2000.Concentrations of sulfate,nitrate,primary organic carbon(POA),secondary organic carbon(SOA),black carbon(BC)aerosols,and tropospheric O3 for the years 1950 and 2000 are obtained a priori by coupled chemistry-aerosol-GCM simulations,and then monthly concentrations are in- terpolated linearly between 1951 and 2000.The annual concentrations of GHGs are taken from the IPCC Third Assessment Report.BC aerosol is internally mixed with other aerosols.Model results indicate that the simulated climate change over 1951–2000 is sensitive to anthropogenic changes in atmospheric components. The predicted year 2000 global mean surface air temperature can differ by 0.8℃ with different forcings. Relative to the climate simulation without changes in GHGs,O3,and aerosols,anthropogenic forcings of SO2- 4 ,BC,BC+SO2- 4 ,BC+SO2- 4 +POA,BC+SO2- 4 +POA+SOA+NO- 3 ,O3,and GHGs are predicted to change the surface air temperature averaged over 1971–2000 in eastern China,respectively,by-0.40°C, +0.62°C,+0.18°C,+0.15°C,-0.78°C,+0.43°C,and+0.85°C,and to change the precipitation,respec- tively,by-0.21,+0.07,-0.03,+0.02,-0.24,-0.08,and+0.10 mm d-1.The authors conclude that all major aerosols are as important as GHGs in influencing climate change in eastern China,and tropospheric O3 also needs to be included in studies of regional climate change in China.
