High sensitivity of anthropogenic aerosol radiative forcing to pre-industrial fire emissions
Abstract
It is widely assumed in global climate models that aerosol emissions from fires were lower in the pre-industrial than the present-day, based on the assumption that emissions increase with population. However, this assumption does not account for how changes in land use and land cover affect the spread of fires, leading to an overall negative relation between global burnt area and human population. Here we show that revised assumptions about pre-industrial fire occurrence have a significant impact on pre-industrial aerosol concentrations and, consequently, the pre-industrial to present-day aerosol radiative forcing. When pre-industrial fire emissions from two global fire models are implemented in a global aerosol model, pre-industrial global mean cloud condensation nuclei concentrations increase substantially relative to simulations using the CMIP6 dataset. We also find that incorporating fire model emissions brings the aerosol model into better agreement with the relative pre-industrial to present-day changes in total black carbon derived from limited northern hemisphere ice core records. Higher pre-industrial aerosol concentrations cause a substantial reduction in the calculated global mean cloud albedo forcing over the industrial period (1750 to 2000) of betweent 35 and 92 percent and a reduction in the direct radiative forcing of between 5 and 10 percent. We conclude that fire emissions consititute one of the largest sources of uncertainty in the calculation of historical aerosol radiative forcing.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.A31C2178C
- Keywords:
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- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0360 Radiation: transmission and scattering;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0365 Troposphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0368 Troposphere: constituent transport and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE