Large changes in biomass burning over the last millennium inferred from paleoatmospheric ethane in polar ice cores

Abstract

Biomass burning drives changes in greenhouse gases, climate-forcing aerosols, and global atmospheric chemistry. There is controversy about the magnitude and timing of changes in biomass burning emissions on millennial time scales from preindustrial to present and about the relative importance of climate change and human activities as the underlying cause. Biomass burning is one of two notable sources of ethane in the preindustrial atmosphere. Here, we present ice core ethane measurements from Antarctica and Greenland that contain information about changes in biomass burning emissions since 1000 CE (Common Era). The biomass burning emissions of ethane during the Medieval Period (1000–1500 CE) were higher than present day and declined sharply to a minimum during the cooler Little Ice Age (1600–1800 CE). Assuming that preindustrial atmospheric reactivity and transport were the same as in the modern atmosphere, we estimate that biomass burning emissions decreased by 30 to 45% from the Medieval Period to the Little Ice Age. The timing and magnitude of this decline in biomass burning emissions is consistent with that inferred from ice core methane stable carbon isotope ratios but inconsistent with histories based on sedimentary charcoal and ice core carbon monoxide measurements. This study demonstrates that biomass burning emissions have exceeded modern levels in the past and may be highly sensitive to changes in climate.

Coherent signature of warming-induced extreme sub-continental boreal wildfire activity 4800 and 1100 years BP

“…Notable fluctuations in biomass burning since 1000 BP are broadly consistent with independent estimates of biomass burning emissions that were recently obtained from paleoatmospheric ethane in Greenland polar ice cores (figures 4(c) and S10; data from Nicewonger et al 2018). Biomass burning is one of two important sources of ethane in the preindustrial atmosphere (Nicewonger et al 2018). This demonstrates the relevance of the information that can be deduced from lake-sediment data for large-scale environmental issues: the correlation between the two independent records implies that fire activity in the study area is an important source for fire emissions transport into Greenland (Kehrwald et al 2012).…”

“…A positive trend in biomass burning during 1750-1950 AD, roughly coinciding with the transition from the Pre-Industrial period to the Anthropocene (~1950 AD), was found across 49% of the area, but mostly limited to the western half ( figure S9). Notable fluctuations in biomass burning since 1000 BP are broadly consistent with independent estimates of biomass burning emissions that were recently obtained from paleoatmospheric ethane in Greenland polar ice cores (figures 4(c) and S10; data from Nicewonger et al 2018). Biomass burning is one of two important sources of ethane in the preindustrial atmosphere (Nicewonger et al 2018).…”

“…(c) Same as (a) but for the normalized charcoal (CHAR norm ) accumulation. The squares illustrate the distribution of Greenland ice core ethane levels from (Nicewonger et al 2018) and are used as an independent fire proxy for benchmarking (also see figure S10 for a zoom of the last 1000 years). The two records are significantly correlated with r=0.62 and bootstrap 95% CI [0.16, 0.86].…”

“…It should be noted that sampling density was not constant through the Holocene, such that uncertainty ranges of the reconstructed temperatures varied with time (Kobashi et al 2017). The relationship between paleoatmospheric ethane in Greenland polar ice cores (Nicewonger et al 2018) and biomass burning was also examined.…”

Quaternary Highlights (September–December 2018)

“…Approximately two-thirds of ethane emissions are due to fossil fuel burning and the remainder derives from biomass burning and seep outgassing. Nicewonger et al [9] use the ethane trapped in Greenland and Antarctica ice cores as a proxy for biomass burning changes from 1000 CE to the present. Maximum levels of biomass burning (significantly higher than today) were recorded during the Medieval Period (1000-1500 CE) and minimum values occurred during the Little Ice Age (1600-1800 CE), when ethane emissions due to biomass burning decreased by 30-45%.…”