I found it, Will !
It was on page 13 of this UN Environment Global Status Report 2017 report https://www.worldgbc.org/sites/default/files/UNEP%20188_GABC_en%20(web).pdfI referred to it in my article ‘Growth in floor area: the blind spot in cutting carbon’ (Emerald, 2020).
I also seem to recall seeing similar quote on Architecture 2030.
Thanks for reminding me of this again.
David