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SUMMARY:The effects of ozone depletion\, increased greenhouse gas emission
 s\, and increased aerosols on precipitation in High-Mountain Asia - Zoran 
 E.H. Kaufmann\, EPFL\, Environmental Sciences and Engineering\, Switzerlan
 d
DTSTART:20170221T140000Z
DTEND:20170221T150000Z
UID:TALK70744@talks.cam.ac.uk
CONTACT:Dr Alexandra Weiss
DESCRIPTION:High-Mountains Asia (HMA) forms the largest mountain mass on E
 arth and provides the water needs for more than one billion people living 
 in downstream regions. They play a crucial role by interacting with region
 al atmospheric circulations\, such as the summer monsoon and winter mid- l
 atitude westerlies. However\, despite the importance of precipitation in t
 his region our understanding of how human-related activities such as ozone
  depletion\, increasing greenhouse gas (GHG) concentrations and aerosol lo
 ading influences precipitation are still uncertain. In particular\, althou
 gh studies have tried to explain the sensitivity of precipitation in HMA d
 ue to e.g. aerosols and GHG\, no study has additionally investigated the e
 ffect of all anthropogenic forcings (i.e. a combination of increasing GHG\
 , ozone depletion\, and aerosols).\n\nThis study undertakes an analysis of
  five global atmosphere-only climate simulations (which use forcing repres
 entative of pre-industrial conditions\, present-day ozone depletion\, pres
 ent-day GHG concentrations\, present-day aerosol concentrations\, and ‘a
 ll’ present-day anthropogenic forcing) to explore the sensitivity of the
  distribution of precipitation over HMA\, and particularly the Hindu- Kush
  Karakoram (HKK) and Himalaya regions. The analysis indicates a complex se
 t of interactions involving increasing GHG and anthropogenic aerosols affe
 cts precipitation over the Himalayas in summer\, with a reduction in preci
 pitation caused by anthropogenic aerosols tending to offset increases caus
 ed by increasing GHG. It is further shown that increasing GHG has a strong
  positive impact in summer in the Himalaya regions below around 2000 m\, w
 hile aerosols decrease precipitation at all altitudes in the Himalayas in 
 summer. Examination of the all forcing experiment suggests that the associ
 ated precipitation response is highly non-linear and regionally varying\, 
 and much more complex than a simple addition of individual effects. By com
 parison\, the various anthropogenic forcings had little influence on winte
 r precipitation.\n\nIt is shown that the increase in summer precipitation 
 over the Himalayas in response to increasing GHG is due to a strengthening
  of the summer monsoon\, while the decrease in precipitation in response t
 o aerosols is due to a weakened circulation. In the all forcing experiment
  the effects on the monsoon due to increasing GHG and aerosols largely off
 set each other. This perhaps suggests that the aerosols also play an impor
 tant role by acting as condensation nuclei and therefore altering cloud di
 stributions.\n\n
LOCATION:British Antarctic Survey\, Room 187
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