Utilizing biofuels as a substitute for heavy fuel oil in the current (2006) global shipping fleet would result in strong reductions in sulfate aerosol of up to about 40-60%, according to a new study by a team from Germany and Hawaii.
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.
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.
—Righi et al.
Presented in a paper in the ACS journal Environmental Science & Technology, the study uses global bottom-up algorithm to calculate geographically resolved emission inventories of gaseous (NOx, CO, SO2) and aerosol (black carbon, organic matter, sulfate) species for different kinds of low-sulfur fuels in shipping.
…one may argue that such a reduction
toward less negative values of RF [radiative forcing] might accelerate global warming
by canceling less of the warming effect caused by increasing
CO2. It should be kept in mind, however, that a simple cancellation
of global warming and cooling effect might not be reasonable
from a physical point of view: the aerosol-induced cloud forcing
is a strongly localized effect, with very high regional variations, while CO2 exerts relatively homogeneous warming
across the hemispheres.
Moreover, the time scales of these two components are very different: CO2 remains in the atmosphere
for many decades, and its climate response could be relevant on
time scales of the order of centuries or more. SO4, on the other
hand, has a residence time in the order of a few days and impacts
the climate only for decades. Climate effects of fuel production,
which might be very different for biofuels and for HFO [heavy fuel oil], are not
considered here. Hence, a complete evaluation of the climatic
impact is not possible, but should be the subject of future
investigations.—Righi et al.
Resources
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Mattia Righi, Carolin Klinger, Veronika Eyring, Johannes Hendricks, Axel Lauer, Andreas Petzold (2011) Climate Impact of Biofuels in Shipping: Global Model Studies of the Aerosol Indirect Effect. Environmental Science & Technology doi: 10.1021/es1036157