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SUMMARY:Can polar bears change Arctic clouds? - Jo Browse\, University of 
 Exeter
DTSTART:20180123T140000Z
DTEND:20180123T150000Z
UID:TALK97039@talks.cam.ac.uk
CONTACT:Dr Gillian Young
DESCRIPTION:A significant uncertainty in our forecasts of Arctic climate i
 s the Arctic cloud response to sea-ice retreat. This uncertainty derives f
 rom multiple factors\, most significantly\, from our lack of understanding
  of the source of high-latitude aerosol (to which Arctic clouds are pecul
 iarly sensitive). It has been suggested that reduction in sea-ice will inc
 rease local emissions of aerosol increasing Arctic cloud albedo through th
 e 1st (>albedo) and 2nd (>lifetime) indirect effects. Potentially Arctic c
 loud brightening may mitigate the ice-albedo feedback to some (unknown) de
 gree. However\, accurately predicting the response of Arctic aerosol and c
 loud to sea-ice retreat is predicated on our understanding of present-day 
 aerosol sources and processes. Observations suggest that Arctic aerosol tr
 ends are driven by a combination of primary and secondary precursor gas em
 issions\, and indicate a complex coupled system involving ice\, ocean\, at
 mospheric and biological processes. It is therefore no surprise that model
 s struggle to reproduce observed Arctic aerosol and clouds. Historically\,
  modellers have ‘filled the gap’ in modelled aerosol with local emissi
 on fluxes or processes which are 'tuned' to observations (varied until the
  model looks 'right'). This tuning process is key to producing skilled mod
 els (akin to calibrating an instrument) however in a system of so many unk
 nowns there is a danger that tuned emissions may be a self-fulfilling prop
 hecy leading to a flawed understanding of Arctic aerosol and cloud.  Here
 \, I will discuss the urgent problem with Arctic clouds in global climate 
 model\, introduce novel modelling methods which could inform observations 
 and call for a combined use of modelling and observational techniques acro
 ss diverse fields to (among other issues) understand the likely significan
 t (but unconstrained) role of biological processes (from primary marine or
 ganics to ammonia emissions from bird colonies).
LOCATION:British Antarctic Survey\, Innovation Centre\, Seminar Room 2
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