Reconstruction of Paleofire Emissions Over the Past Millennium From Measurements of Ice Core Acetylene

Abstract

Acetylene is a short‐lived trace gas produced during combustion of fossil fuels, biomass, and biofuels. Biomass burning is likely the only major source of acetylene in the preindustrial atmosphere, making ice core acetylene a powerful tool for reconstructing paleofire emissions. Here we present a 2,000‐year atmospheric record of acetylene reconstructed from analysis of air bubbles trapped in Greenland and Antarctic ice cores and infer pyrogenic acetylene emissions using a chemistry transport model. From 0 to 1500 CE, Antarctic acetylene averages 36 ± 1 pmol mol−1 (mean ± 1 SE), roughly double the annual mean over Antarctica today. Antarctic acetylene declines during the Little Ice Age by over 50% to 17 ± 2 pmol mol−1 from 1650 to 1750 CE. Acetylene over Greenland declines less dramatically over the same period. Modeling results suggest that pyrogenic acetylene emissions during 1000–1500 CE were sustained at rates significantly greater than modern day and declined by over 50% during the 1650–1750 CE period.

Extracting a History of Global Fire Emissions for the Past Millennium From Ice Core Records of Acetylene, Ethane, and Methane

“…Consequently, transport and removal must be considered in order to estimate the variations in emissions responsible for atmospheric histories derived from ice core data. The UCI-CTM was used to estimate the sensitivity (defined as pmol mol −1 per Tg year −1 emission) of acetylene and ethane levels over Greenland and Antarctica to various sources (Nicewonger et al, 2018(Nicewonger et al, , 2020. Sensitivities were estimated by defining a reference model simulation of the modern atmosphere and adding acetylene-like and ethane-like tracer species (Nicewonger et al, 2018(Nicewonger et al, , 2020.…”

“…The UCI-CTM was used to estimate the sensitivity (defined as pmol mol −1 per Tg year −1 emission) of acetylene and ethane levels over Greenland and Antarctica to various sources (Nicewonger et al, 2018(Nicewonger et al, , 2020. Sensitivities were estimated by defining a reference model simulation of the modern atmosphere and adding acetylene-like and ethane-like tracer species (Nicewonger et al, 2018(Nicewonger et al, , 2020. These tracers react with the same OH lifetime and stratospheric loss rate as acetylene and ethane but do not affect the abundance of OH in the model.…”

“…Ice core trace gas measurements of methane and δ 13 CH 4, ethane, acetylene, and carbon monoxide also have been used to reconstruct trends in global fire emissions over the past millennium ( Figure 2) (Bock et al, 2017;Ferretti et al, 2005;Mischler et al, 2009;Nicewonger et al, 2016Nicewonger et al, , 2018Nicewonger et al, , 2020Sapart et al, 2012;Wang et al, 2010). Methane has an 8-to 10-year atmospheric lifetime and therefore the potential to provide a globally integrated signal of pyrogenic emissions.…”

“…Limited knowledge of the fossil fuel source magnitudes of acetylene and ethane after industrialization makes estimating the biomass burning source of these gases into the modern era highly uncertain (Nicewonger et al, 2018(Nicewonger et al, , 2020. However, qualitatively, the ice cores levels of acetylene and ethane do not show any large changes into the mid-1800s from their mean level in the 1700s, indicating that the sources, including biomass burning, likely stayed low through the end of the nineteenth century ( Figure 2) (Nicewonger et al, 2018(Nicewonger et al, , 2020. In contrast, the CO ice core record indicates increased biomass burning emissions around the late-1800s, consistent with the temporal trends found in the charcoal proxy record.…”

“…In contrast, the CO ice core record indicates increased biomass burning emissions around the late-1800s, consistent with the temporal trends found in the charcoal proxy record. The exact cause of the differences between the ice core acetylene, ethane, and methane records with the CO record has not yet be determined (Nicewonger et al, 2018(Nicewonger et al, , 2020 and until co-measurements of all these gases are made in the same ice core, it may be challenging to resolve.…”