Decadal Warning Systems - Reducing Disaster: Early Warning Systems for Climate Change - page 301

Fig. 16.3 Observed Atlantic multi-decadal variability ( AMV ) and potential climate impacts. ( a )
Time series of AMV measured by detrended 9-year mean sea surface temperature averaged over
the North Atlantic Ocean. ( b - g ) Composite differences between positive ( magenta squares in ( a ))
and negative ( cyan squares in ( a )) phases of AMV, for boreal winter (DJF, b - d ) and summer (JJA,
e - g ). Units are standard deviations (Adapted from Smith et al. 2012a )
Observations indicate that North Atlantic sea surface temperatures (SSTs)
fl uctuate with a period of about 30-80 years, often referred to as Atlantic Multi-
decadal Variability (AMV) or the Atlantic Multi-decadal Oscillation (AMO).
Observations (see Fig. 16.3 ) and modelling studies (Sutton and Hodson 2005 ;
Zhang and Delworth 2006 ; Knight et al. 2006 ; Dunstone et al. 2011 ; Robson et al.
2012 , 2013 ) suggest that important climate impacts, including rainfall over the
African Sahel, India and Brazil, Atlantic hurricanes and climate over Europe and
America, are potentially driven by AMV. Climate models suggest that AMV can
vary naturally, linked to variations of ocean currents that form the Atlantic
Meridional Overturning Circulation (AMOC, Delworth et al. 2007 ; Knight et al.
2005 ; Vellinga and Wu 2004 ; Jungclaus et al. 2005 ). Idealized experiments, which
assess the predictability of a climate model rather than the real world, suggest that
natural fl uctuations of the AMOC and AMV are potentially predictable at least a
few years ahead (Griffi es and Bryan 1997 ; Pohlmann et al. 2004 ; Collins et al. 2006 ;
Dunstone and Smith 2010 ). AMV may also be infl uenced by external factors includ-
ing volcanoes (Stenchikov et al. 2009 ; Otterå et al. 2010 ), greenhouse gases (IPCC
2007 ) and anthropogenic aerosols (Booth et al. 2012 ).
Pacifi c SSTs also vary on decadal timescales, referred to as the Pacifi c Decadal
Oscillation (PDO, Mantua et al. 1997 ), the Interdecadal Pacifi c Oscillation (IPO,
Folland et al. 2002 ) or Pacifi c Decadal Variability (PDV). PDV has been linked to
important climate impacts, including rainfall over America, Asia, Africa and