Dynamical response of Mediterranean precipitation to greenhouse gases and aerosols
Atmospheric aerosols and greenhouse gases affect cloud properties, radiative balance and, thus, the hydrological cycle. Observations show that precipitation has decreased in the Mediterranean since the beginning of the 20th century, and many studies have investigated possible mechanisms. So far,...
| Main Authors: | , , , , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-06-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/8439/2018/acp-18-8439-2018.pdf |
| Summary: | Atmospheric aerosols and greenhouse gases affect cloud properties, radiative
balance and, thus, the hydrological cycle. Observations show that
precipitation has decreased in the Mediterranean since the beginning of the
20th century, and many studies have investigated possible mechanisms. So far,
however, the effects of aerosol forcing on Mediterranean precipitation remain
largely unknown. Here we compare the modeled dynamical response of
Mediterranean precipitation to individual forcing agents in a set of global
climate models (GCMs). Our analyses show that both greenhouse gases and
aerosols can cause drying in the Mediterranean and that precipitation is
more sensitive to black carbon (BC) forcing than to well-mixed greenhouse
gases (WMGHGs) or sulfate aerosol. In addition to local heating, BC appears
to reduce precipitation by causing an enhanced positive sea level pressure (SLP)
pattern similar to the North Atlantic
Oscillation–Arctic Oscillation, characterized by higher SLP at midlatitudes and lower SLP at
high latitudes. WMGHGs cause a similar SLP change, and both are associated
with a northward diversion of the jet stream and storm tracks, reducing
precipitation in the Mediterranean while increasing precipitation in northern
Europe. Though the applied forcings were much larger, if forcings are scaled
to those of the historical period of 1901–2010, roughly one-third (31±17 %) of the precipitation decrease would be attributable to global BC
forcing with the remainder largely attributable to WMGHGs, whereas global
scattering sulfate aerosols would have negligible impacts. Aerosol–cloud
interactions appear to have minimal impacts on Mediterranean precipitation in
these models, at least in part because many simulations did not fully include such
processes; these merit further study. The findings from this study suggest
that future BC and WMGHG emissions may significantly affect regional water
resources, agricultural practices, ecosystems and the economy in the
Mediterranean region. |
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| ISSN: | 1680-7316 1680-7324 |