Improved biomass burning emissions from 1750 to 2010 using ice core records and inverse modeling

Abstract

Estimating fire emissions prior to the satellite era is challenging because observations are limited, leading to large uncertainties in the calculated aerosol climate forcing following the preindustrial era. This challenge further limits the ability of climate models to accurately project future climate change. Here, we reconstruct a gridded dataset of global biomass burning emissions from 1750 to 2010 using inverse analysis that leveraged a global array of 31 ice core records of black carbon deposition fluxes, two different historical emission inventories as a priori estimates, and emission-deposition sensitivities simulated by the atmospheric chemical transport model GEOS-Chem. The reconstructed emissions exhibit greater temporal variabilities which are more consistent with paleoclimate proxies. Our ice core constrained emissions reduced the uncertainties in simulated cloud condensation nuclei and aerosol radiative forcing associated with the discrepancy in preindustrial biomass burning emissions. The derived emissions can also be used in studies of ocean and terrestrial biogeochemistry.

Fig. 1. Temporal trends of biomass burning (BB) refractory black carbon (rBC) emissions from 1750 to 2010.

a, b Temporal trends of a priori emissions by regions for the BB4CMIP and LPJ-LMfire inventories. c, d Temporal trends of a posteriori emissions by regions. e, f The difference between a posteriori emissions and a priori emissions in different regions. Definitions of region acronyms are given in Table 1.

Fig. 2. Comparisons of measured and modeled trends of refractory black carbon (rBC) deposition fluxes.

a Comparisons with 14 Antarctica ice cores and (b) with 11 Greenland ice cores. The trends are shown as ratios of historical rBC flux to the present-day (PD) values (relative to the average value of the period from 1997 to 2010). The gray lines represent the median values of the measured ratios from ice core records, and the gray areas represent the 25^th to 75^th percentile range across sites. The modeled deposition flux is calculated using the product of the Jacobian matrix (K) and the emission vector (x) (see “Methods”). The two historical biomass-burning emissions inventories are BB4CMIP and LPJ-LMfire; the CEDS inventory includes fossil fuel and biofuel emissions.

Fig. 3. Comparisons of biomass burning (BB) refractory black carbon (rBC) emissions, cloud condensation nuclei (CCN) concentrations, and cloud albedo forcing (CAF) using a priori and a posteriori BB emissions.

a–c Average rBC emissions during the preindustrial period (PI, 1750-1780) for (a) global, (b) North Hemisphere (NH), and (c) South Hemisphere (SH). The error bars represent the 2.5% and 97.5% range calculated by Monte Carlo simulations (Methods). d–f Average CCN concentration simulated by GEOS-Chem-TOMAS during PI (1750-1780) for global (d), NH (e), and SH (f). g–i Average CAF for PD (present day, 1997-2010) relative to PI (1750-1780) calculated by RRTMG radiative transfer model for global (g), NH (h), and SH (i).