“…Emulators are usually constructed using regression, with coefficients calibrated from an ensemble of simulations with different parameter settings (e.g. Murphy et al, 2004Murphy et al, , 2007Kennedy et al, 2006;Rougier and Sexton, 2007;Rougier et al, 2009;, though neural networks have also been used (e.g. Knutti et al, 2003;Piani et al, 2005;Sanderson et al, 2008).…”