Land Use Change Impacts on Air Quality and Climate* AGU Fall Meeting December 19, 2014 Colette L. Heald Dominick V. Spracklen *review article submitted to Chemical Reviews

Land Use Change and Atmospheric Composition NH 3 Soil NO x O3O3 PBAP Dust Smoke * Impacts on LLGHG and secondary impacts via changes in transport/meteorology not considered here BVOC Deposition

Historical Changes in Aerosol (Precursor) Emissions: Pre-Industrial to Present Day NH 3 Soil NO x PBAP Dust Smoke BVOC Monoterpenes: 0% (Acosta Navarro et al., 2014) Isoprene: -15 to -36% (Unger et al., 2013; Lathiere et al., 2010) -11 to -30% (Kloster et al., 2010; Yang et al., 2014) +50% (Yienger and Levy, 1995) +170% (RCP emissions) +18 to +25% (Ward et al., 2014; Ginoux et al., 2012)

Historical Changes in Aerosol Radiative Effect Associated with Land Use Change ( ) Historical land use change has likely led to a global mean aerosol cooling equivalent to 10-50% of the radiative forcing driven by anthropogenic emissions

Historical and Projected Global Land Use Change based on Lawrence et al. (2012) Historical global trend of cropland expansion at the expense of forests and grasslands, may continue through 21 st century or reverse.

Projected Changes in Aerosol (Precursor) Emissions: Present Day to 2100 NH 3 Soil NO x PBAP Dust Smoke BVOC Monoterpenes: 0 to +12% (Wu et al., 2012; Heald et al., 2008) Isoprene: -24 to -27% (Wu et al., 2012; Heald et al., 2008; Arneth et al., 2008) -11 to -41% (Kloster et al., 2012) +60% (Yienger and Levy, 1995) +28 to +105% (RCP projections) +5 to +10% (Ward et al., 2014)

Projected Changes in Aerosol Radiative Effect Associated with Land Use Change ( ) Land use change driven aerosol cooling likely to continue through 21 st century, but subject to large uncertainties in agricultural practices and fire activity.

Scenario: Tropical Deforestation Deforestation switches forests from a cooling (SOA) to a warming (maintenance burning), switch relatively insensitive to assumptions, but implied [SOA] is high. BVOC EFs: Guenther et al., 2012 BB EFs: Akagi et al., 2011 Biomass Fuel: various DRF efficiencies: AeroCom II (Myhre et al., 2013) SOA yields: 1% isoprene, 15% monoterpenes

Scenario: Palm Oil Plantation Palm oil conversion likely to happen much faster. Converts forest from marginally cooling to warming. SOA is less of a factor (isoprene emissions lower in Asian tropical forests), ignoring NOx dependence of yields. Degree of warming critically depends on the biomass of crop residues burned. BVOC EFs: Guenther et al., 2012 BB EFs: Akagi et al., 2011 Biomass Fuel: various DRF efficiencies: AeroCom II (Myhre et al., 2013) SOA yields: 1% isoprene, 15% monoterpenes

Scenario: Boreal Forest Fire and Succession Strong pulse of cooling. Forest eventually returns to initial state. Wildfire land use transitions based on Rogers et al., (2013) BVOC EFs: Guenther et al., 2012 BB EFs: Akagi et al., 2011 Biomass Fuel: various DRF efficiencies: AeroCom II (Myhre et al., 2013) SOA yields: 1% isoprene, 15% monoterpenes

Scenario: Mid-Latitude Clearing for Agriculture Sensitive to agricultural practices: the balance between fertilizer application/volatilization vs. the fraction of crop residues burned. *assumed here that sufficient SOx and NOx in the atmosphere to convert ammonia to ammonium This time period lasts decades longer BVOC EFs: Guenther et al., 2012 BB EFs: Akagi et al., 2011 Biomass Fuel: various DRF efficiencies: AeroCom II (Myhre et al., 2013) SOA yields: 1% isoprene, 15% monoterpenes

[Heald and Spracklen, Chemical Reviews, in press] Historical land use change impacts on aerosols equivalent to ~30% of emissions-driven radiative forcing. In an era of decreasing anthropogenic emissions, land use change will become an increasingly important driver of aerosol-climate impacts. Our understanding of land use change impacts on air quality is limited, more studies needed! Historical land use change impacts on aerosols equivalent to ~30% of emissions-driven radiative forcing. In an era of decreasing anthropogenic emissions, land use change will become an increasingly important driver of aerosol-climate impacts. Our understanding of land use change impacts on air quality is limited, more studies needed!