Climate Impact of Biofuels in Shipping: Global Model Studies of the Aerosol Indirect Effect

Abstract

Aerosol emissions from international shipping are recognized to have a large impact on the Earth's radiation budget, directly by scattering and absorbing solar radiation and indirectly by altering cloud properties. New regulations have recently been approved by the International Maritime Organization (IMO) aiming at progressive reductions of the maximum sulfur content allowed in marine fuels from current 4.5% by mass down to 0.5% in 2020, with more restrictive limits already applied in some coastal regions. In this context, we use a global bottom-up algorithm to calculate geographically resolved emission inventories of gaseous (NO(x), CO, SO(2)) and aerosol (black carbon, organic matter, sulfate) species for different kinds of low-sulfur fuels in shipping. We apply these inventories to study the resulting changes in radiative forcing, attributed to particles from shipping, with the global aerosol-climate model EMAC-MADE. The emission factors for the different fuels are based on measurements at a test bed of a large diesel engine. We consider both fossil fuel (marine gas oil) and biofuels (palm and soy bean oil) as a substitute for heavy fuel oil in the current (2006) fleet and compare their climate impact to that resulting from heavy fuel oil use. Our simulations suggest that ship-induced surface level concentrations of sulfate aerosol are strongly reduced, up to about 40-60% in the high-traffic regions. This clearly has positive consequences for pollution reduction in the vicinity of major harbors. Additionally, such reductions in the aerosol loading lead to a decrease of a factor of 3-4 in the indirect global aerosol effect induced by emissions from international shipping.

Real-case simulations of aerosol–cloud interactions in ship tracks over the Bay of Biscay

“…This is consistent with the equivalent increase of aerosol number concentration within the size range of activation in these simulations. This result is contradictory to global studies (Righi et al, 2011;Peters et al, 2012), where a high sensitivity of the aerosolcloud interactions to the aging of the prescribed emissions was found. The cause for these different sensitivities remains to be addressed.…”

“…Global general circulation model (GCM) simulations yield globally averaged ACIs due to ship emissions between −0.6 and −0.07 Wm −2 (Lauer et al, 2007;Righi et al, 2011;Peters et al, 2012;Partanen et al, 2013). Given the maximum simulated cooling effect, ACI induced by shipping emissions could significantly contribute to the current best estimate of globally averaged ACI (−0.45 Wm −2 , Myhre et al, 2013).…”

“…In the present simulations, the PM and SO 2 emission mass fluxes were emitted in one level ∼ 160 m above the surface (e.g. Peters et al, 2012) with a log-normal size distribution (σ = 1.59) and two different size specifications (Righi et al, 2011;Lund et al, 2012) shown in Table 1. Both size distributions, fresh and aged, are inferred from measurements and attempt to include coagulation effects of the aerosol as time progresses.…”

Aerosol indirect effects from shipping emissions: sensitivity studies with the global aerosol-climate model ECHAM-HAM

“…In their simulations, a reduction of the globally averaged fuel sulfur content from 2.7 % (in 2002) to 0.5 % (in 2012) lead to a reduction of globally averaged AIEs from shipping emissions from about −0.43 to about −0.27 W m −2 despite an annual growth rate of fuel consumption of 4.1 %. Applying a model environment completely identical to Lauer et al (2007) and Lauer et al (2009), Righi et al (2011 the shipping emission induced AIE to range from −0.40 to −0.28 W m −2 -despite the total assumed fuel consumption, and thus emissions, being higher than in Lauer et al (2007). Righi et al (2011) attribute this difference in obtained AIE to the use of a different geographical distribution of the shipping emissions.…”

“…Applying a model environment completely identical to Lauer et al (2007) and Lauer et al (2009), Righi et al (2011 the shipping emission induced AIE to range from −0.40 to −0.28 W m −2 -despite the total assumed fuel consumption, and thus emissions, being higher than in Lauer et al (2007). Righi et al (2011) attribute this difference in obtained AIE to the use of a different geographical distribution of the shipping emissions. The DRE resulting from shipping emissions is small and estimated to range from −47.5 to −9.1 m W m −2 (Balkanski et al, 2010;Eyring et al, 2010).…”