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SUMMARY:The search for signs of ozone recovery - Dr James Keeble\, Cambrid
 ge University
DTSTART:20180514T131500Z
DTEND:20180514T141500Z
UID:TALK105121@talks.cam.ac.uk
CONTACT:Paul Griffiths
DESCRIPTION:2017 marked the 30th anniversary of the Montreal Protocol\, wh
 ich was\nimplemented to protect the stratospheric ozone layer from the har
 mful\neffects of ozone depleting substances (ODS). Controls introduced und
 er\nthe Montreal Protocol and its subsequent amendments first slowed the\n
 rate of accumulation of these halogenated ODS in the atmosphere\, and\nsin
 ce the late 1990s their atmospheric concentrations have begun to\ndecline.
   A reduction in stratospheric chlorine concentrations should\nlead to an 
 increase in atmospheric ozone as the strength of the halogen\ncatalyzed oz
 one destruction cycles declines. However\, detecting recovery\nof the stra
 tospheric ozone layer is complicated by a number of\nadditional factors wh
 ich affect the year to year variability of total\ncolumn ozone values (e.g
 . volcanic eruptions\, the solar cycle\, the\nquasi-biennial oscillation a
 nd the El Niño-Southern Oscillation).  As a\nresult of these factors\, id
 entifying robust recovery of total column\nozone and ascribing that recove
 ry to a decline in stratospheric halogen\nspecies is a complex issue.\n\nI
 n this study\, total column ozone values from an ensemble of UM-UKCA\nmode
 l simulations are examined to investigate different definitions of\nprogre
 ss on the road to ozone recovery: (i) a slowed rate of decline and\nthe da
 te of minimum column ozone\; (ii) the identification of significant\nposit
 ive trends\; and (iii) a return to historic values.  Focus is then\nmoved 
 to the tropics\, where ozone recovery resulting from declining\nstratosphe
 ric chlorine concentrations may be offset by circulation\nchanges resultin
 g from increasing greenhouse gas concentrations.
LOCATION:Pfizer Lecture Theatre\, Department of Chemistry
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