Abstract View
Improved Estimates of Preindustrial Biomass Burning Reduce the Magnitude of Aerosol Climate Forcing in the Southern Hemisphere
PENGFEI LIU, Jed Kaplan, Loretta Mickley, Yang Li, Nathan Chellman, Monica Arienzo, Jack Kodros, Jeffrey R. Pierce, Michael Sigl, Johannes Freitag, Robert Mulvaney, Mark Curran, Joseph McConnell, Harvard University
Abstract Number: 507
Working Group: Aerosols, Clouds and Climate
Abstract
Fire plays a pivotal role in shaping terrestrial ecosystems and the chemical composition of the atmosphere, and thus influences Earth’s climate. Although contemporary patterns and causes of wildfire are well understood, the trend and magnitude of fire activity over the last few centuries are controversial. This uncertainty in past fire-related aerosol emissions hinders understanding of preindustrial to present-day aerosol radiative forcing because the aerosol baseline largely depends on estimates of preindustrial biomass burning. Here we present new evidence from a broad array of 14 Antarctic ice cores and 1 central Andean ice core, suggesting that historical fire emissions in the Southern Hemisphere (SH) significantly exceeded present-day levels. To understand this observation, we use a global fire model to show that overall SH fire emissions could have declined by 30% over the 20th century, possibly because of the rapid expansion of land use for agriculture and animal production. Results from atmospheric chemistry transport and deposition model simulations using our new scenario of declining fire emissions show significantly improved agreement with the ice-core records, compared to similar model results obtained with widely used emission estimates that suggest SH fire increased over the last century. We further show that the decreasing trend in fire emissions largely compensates for the cooling effect of increasing aerosols from other anthropogenic sources. The estimated magnitude of total aerosol forcing in the SH since the 1750s is 42% less than that based on an emission inventory widely used in climate models.