Yunha Lee

Evaluation of multi-model black carbon from ACCMIP preindustrial to present-day 
simulations
   
   As part of the Atmospheric Chemistry and Climate Model Intercomparison 
Project (ACCMIP), we evaluate the historical black carbon (BC) aerosols simulated 
by 8 ACCMIP models against observations including 12 ice core records, long-term 
atmospheric surface mass concentrations and recent Arctic BC snowpack 
measurements. We also estimate BC albedo forcing by performing additional 
simulations using offline models with prescribed meteorology from 1996-2000. We 
evaluated the vertical profile of BC snow concentrations from these offline 
simulations using the recent BC snowpack measurements.
   Despite using the same BC emissions, the global BC burden differs by 
approximately a factor of 3 among models due to differences in aerosol removal 
parameterizations and simulated meteorology. However, the global BC burden from 
preindustrial to present-day increases by 2.5-3 times with little variation among 
models, roughly matching the 2.5-fold increase in total BC emissions during the 
same period. The ACCMIP simulations match the observed atmospheric BC surface 
mass concentrations generally well in Europe and North America but fail to predict 
the Arctic BC seasonality due to severe underestimations during winter and spring. 
The simulated BC snow concentrations are, on average, within a factor of 2-3 of the 
BC snowpack measurements except for Greenland and the Arctic Ocean. For the ice 
core evaluation, models tend to capture both the observed temporal trends and the 
magnitudes well at Greenland sites but less in other sites. Despite a large divergence 
in BC deposition at two Antarctic ice core sites, models are able to capture the 
relative increase from preindustrial to present-day seen in the ice cores. 
   In 2000 relative to 1850, globally annually averaged BC surface albedo forcing 
from the offline simulations ranges from 0.014 to 0.019 W m-2 among the ACCMIP 
models. Comparing offline and online BC albedo forcings computed by some of the 
same models, we find that the global annual mean can vary by up to a factor of two 
because of different aerosol models or different BC-snow parameterizations and 
snow cover. The spatial distributions of the offline BC albedo forcing in 2000 show 
especially high BC forcing (i.e., over 0.1 W m-2) over Manchuria, Karakoram, and 
most of the Former USSR. Models predict the highest global annual mean BC forcing 
in 1980 rather than 2000, mostly driven by the high fossil fuel and biofuel emissions 
in the Former USSR in 1980.