“…Of these elements, uncertainty seems to be the key (de Sadeleer, 2007c, p. 4; Scott, 2005a, p. 57; Sunstein, 2005, p. 24). Although, uncertainty may be broadly defined to include ignorance, some minimal apprehension of risk, in other words some form of threshold uncertainty, must exist to trigger the PP (Barrett, 1999, p. 63; Kiss and Shelton, 2004, p. 212; Ricci et al , 2003, p. 5; Steele, 2006, p. 19; Sunstein, 2005, p. 24; Trouwborst, 2006, p. 117) 10…”