Aerosols at the poles: an AeroCom Phase II multi-model evaluation
Atmospheric aerosols from anthropogenic and natural sources reach the polar regions through long-range transport and affect the local radiation balance. Such transport is, however, poorly constrained in present-day global climate models, and few multi-model evaluations of polar anthropogenic aer...
Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2017-10-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | https://www.atmos-chem-phys.net/17/12197/2017/acp-17-12197-2017.pdf |
Summary: | Atmospheric aerosols from anthropogenic and natural
sources reach the polar regions through long-range transport and affect the
local radiation balance. Such transport is, however, poorly constrained in
present-day global climate models, and few multi-model evaluations of polar
anthropogenic aerosol radiative forcing exist. Here we compare the aerosol
optical depth (AOD) at 550 nm from simulations with 16 global aerosol models
from the AeroCom Phase II model intercomparison project with available
observations at both poles. We show that the annual mean multi-model median
is representative of the observations in Arctic, but that the intermodel
spread is large. We also document the geographical distribution and seasonal
cycle of the AOD for the individual aerosol species: black carbon (BC) from
fossil fuel and biomass burning, sulfate, organic aerosols (OAs), dust, and
sea-salt. For a subset of models that represent nitrate and secondary
organic aerosols (SOAs), we document the role of these aerosols at high
latitudes.<br><br>The seasonal dependence of natural and anthropogenic aerosols differs with
natural aerosols peaking in winter (sea-salt) and spring (dust), whereas AOD
from anthropogenic aerosols peaks in late spring and summer. The models
produce a median annual mean AOD
of 0.07 in the Arctic (defined here as north of 60° N). The models
also predict a noteworthy aerosol transport to the Antarctic (south of
70° S) with a resulting AOD varying between 0.01 and 0.02. The
models have estimated the shortwave anthropogenic radiative forcing
contributions to the direct aerosol effect (DAE) associated with BC and OA
from fossil fuel and biofuel (FF), sulfate, SOAs, nitrate, and biomass
burning from BC and OA emissions combined. The Arctic modelled annual mean
DAE is slightly negative (−0.12 W m<sup>−2</sup>), dominated by a positive
BC FF DAE in spring and a negative sulfate DAE in summer. The Antarctic DAE
is governed by BC FF. We perform sensitivity experiments with one of the
AeroCom models (GISS modelE) to investigate how regional emissions of BC and
sulfate and the lifetime of BC influence the Arctic and Antarctic AOD.
A doubling of emissions in eastern Asia results in a 33 % increase in
Arctic AOD of BC. A doubling of the BC lifetime results in a 39 %
increase in Arctic AOD of BC. However, these radical changes still fall
within the AeroCom model range. |
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ISSN: | 1680-7316 1680-7324 |