Abstract. The effect of aerosols is one of many uncertain factors in projections of
future climate. However, the behaviour of mineral dust aerosols (dust) can be
investigated within the context of past climate change. The Last Glacial
Maximum (LGM) is known to have had enhanced dust deposition in comparison
with the present, especially over polar regions. Using the Model for
Interdisciplinary Research on Climate Earth System Model (MIROC-ESM), we
conducted a standard LGM experiment following the protocol of the
Paleoclimate Modelling Intercomparison Project phase 3 and sensitivity
experiments. We imposed glaciogenic dust on the standard LGM experiment and
investigated the impacts of glaciogenic dust and non-glaciogenic dust
on the LGM climate. Global mean radiative perturbations by glaciogenic and
non-glaciogenic dust were both negative, consistent with previous studies.
However, glaciogenic dust behaved differently in specific regions; e.g. it
resulted in less cooling over the polar regions. One of the major reasons for
reduced cooling is the ageing of snow or ice, which results in albedo
reduction via high dust deposition, especially near sources of high
glaciogenic dust emission. Although the net radiative perturbations in the
lee of high glaciogenic dust provenances are negative, warming by the ageing of
snow overcomes this radiative perturbation in the Northern Hemisphere. In
contrast, the radiative perturbation due to high dust loading in the
troposphere acts to warm the surface in areas surrounding Antarctica,
primarily via the longwave aerosol–cloud interaction of dust, and it is
likely the result of the greenhouse effect attributable to the enhanced cloud
fraction in the upper troposphere. Although our analysis focused mainly on
the results of experiments using the atmospheric part of the MIROC-ESM, we
also conducted full MIROC-ESM experiments for an initial examination of the
effect of glaciogenic dust on the oceanic general circulation module. A
long-term trend of enhanced warming was observed in the Northern Hemisphere
with increased glaciogenic dust; however, the level of warming around
Antarctica remained almost unchanged, even after extended coupling with the
ocean.
Effect of high dust amount on surface temperature during the Last Glacial Maximum: a modelling study using MIROC-ESM