Emulating the effect of land-based transport emissions on aerosol-induced radiative forcing change based on a perturbed parameter ensemble method

Emissions from transport contribute significantly to anthropogenic climate change, and evaluating the climate effect induced by aerosols from transport in different emission scenarios usually relies on computing-intensive general circulation models (GCMs). As an alternative approach, simple climate response functions between the emissions from a given sector and their resulting climate impact are desirable, to evaluate emissions scenarios in a more efficient way.

In this study, the Perturbed Parameter Ensemble (PPE) method is applied to generate such simple response functions (emulators), based on simulations with the global aerosol–chemistry–climate model EMAC equipped with the aerosol microphysical submodel MADE3. Emission rates of four species from land-based transport emissions (NO_x, SO₂, black carbon and organic carbon) are varied simultaneously across a four-dimensional parameter space using the Latin Hypercube method, which generates 41 representative combinations. Global model simulations are conducted for each of these combinations and used to train Gaussian Process (GP) emulators that represent the aerosol climate effects arising from emission changes. Finally, a variance-based sensitivity analysis is performed to quantify the relative contributions of individual emission parameters to the aerosol-induced radiative forcing change.

The emulators are generated and evaluated separately in five world regions: Europe, Asia, North America, South America, and the rest of the world. The results demonstrate that the emulators successfully capture the relationship between aerosol-climate effects and emissions and accurately reproduce the model results. The results further reveal pronounced regional differences in the relative contributions of emission parameters to the aerosol climate effect. In South America, organic carbon emissions account for approximately 55% of the land-transport-induced climate effect, with SO₂ contributing the remaining ~45%. By contrast, in all other regions, SO₂ contributes more than 90% and represents the dominant emission parameter driving the aerosol-induced change in radiative forcing.