Evaluation of preindustrial to present-day black carbon and its albedo forcing from Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP)

摘要

As part of the Atmospheric Chemistry and Climate Model IntercomparisonProject (ACCMIP), we evaluate the historical black carbon (BC) aerosolssimulated by 8 ACCMIP models against observations including 12 ice corerecords, long-term surface mass concentrations, and recent Arctic BCsnowpack measurements. We also estimate BC albedo forcing by performingadditional simulations using offline models with prescribed meteorology from1996–2000. We evaluate the vertical profile of BC snow concentrations fromthese offline simulations using the recent BC snowpack measurements.Despite using the same BC emissions, the global BC burden differs byapproximately a factor of 3 among models due to differences in aerosolremoval parameterizations and simulated meteorology: 34 Gg to 103 Gg in 1850and 82 Gg to 315 Gg in 2000. However, the global BC burden frompreindustrial to present-day increases by 2.5–3 times with little variationamong models, roughly matching the 2.5-fold increase in total BC emissionsduring the same period. We find a large divergence among models at bothNorthern Hemisphere (NH) and Southern Hemisphere (SH) high latitude regionsfor BC burden and at SH high latitude regions for deposition fluxes. TheACCMIP simulations match the observed BC surface mass concentrations well inEurope and North America except at Ispra. However, the models fail topredict the Arctic BC seasonality due to severe underestimations duringwinter and spring. The simulated vertically resolved BC snow concentrationsare, on average, within a factor of 2–3 of the BC snowpack measurementsexcept for Greenland and the Arctic Ocean.For the ice core evaluation, models tend to adequately capture both theobserved temporal trends and the magnitudes at Greenland sites. However,models fail to predict the decreasing trend of BC depositions/ice coreconcentrations from the 1950s to the 1970s in most Tibetan Plateau icecores. The distinct temporal trend at the Tibetan Plateau ice coresindicates a strong influence from Western Europe, but the modeled BCincreases in that period are consistent with the emission changes in EasternEurope, the Middle East, South and East Asia. At the Alps site, thesimulated BC suggests a strong influence from Europe, which agrees with theAlps ice core observations. At Zuoqiupu on the Tibetan Plateau, modelssuccessfully simulate the higher BC concentrations observed during thenon-monsoon season compared to the monsoon season but overpredict BC in bothseasons. Despite a large divergence in BC deposition at two Antarctic icecore sites, some models with a BC lifetime of less than 7 days are able tocapture the observed concentrations.In 2000 relative to 1850, globally and annually averaged BC surface albedoforcing from the offline simulations ranges from 0.014 to 0.019 W m?2among the ACCMIP models. Comparing offline and online BC albedo forcingscomputed by some of the same models, we find that the global annual mean canvary by up to a factor of two because of different aerosol models ordifferent BC-snow parameterizations and snow cover. The spatialdistributions of the offline BC albedo forcing in 2000 show especially highBC forcing (i.e., over 0.1 W m?2) over Manchuria, Karakoram, and mostof the Former USSR. Models predict the highest global annual mean BC forcingin 1980 rather than 2000, mostly driven by the high fossil fuel and biofuelemissions in the Former USSR in 1980.