Whether the Walker circulation is slowing down is still a question of much debate. There are now more recent studies which advocate that WC is actually strengthening (LHeureux et al 2013; Kosaka & Xie, 2013), which contradict e.g. Vecchi et al. 2006 and Tokinaga et al 2012), and which may be more consistent with the observed higher SL trend over the western Pacific warm pool region (~east of Indonesia-Philippines) (e.g. Merrifield et al 2012, and others). I tend to think that probably the latter ideas are more correct. If you are interested, see these literature in my PJC (Princeton Journal Club) ftp site ftp://profs.princeton.edu/leo/journals/: