• Exceptionally weak industrial-era AMOC (caused by weak LSW and ISOW). • Has AMOC weakening continued through the 20th century? Relative cooling of SPG may be related to horizontal gyre circulation rather than deep components of AMOC. • Unprecedented 20th century changes in subpolar gyre circulation caused pronounced changes in Northeast Atlantic hydrography and ecosystems. • Recent variability is not simply ‘typical ongoing decadal variability’. Likely future no-analogue conditions. Reliance on climate model projections. • Better understanding of post Little Ice Age and 20th century changes is required for assessing climate model sensitivity and projections of AMOC.