evidence: Contrast this with the results of the Intergovernmental Panel on Climate Change’s Third and Fourth Assessment Reports, which state unequivocally that average global temperatures have risen (Houghton et al. 2001; Alley et al. 2007). [...] This is consistent with the analysis of historian Spencer Weart, who concluded that scientists achieved consensus in 1995 (see Weart 2008). [...] This is evident when the three IPCC assessments—1990, 1995, 2001—are compared (Houghton et al. 1990, 2001; Bruce et al. 1996; Watson et al. 1996; Metz et al. 2001; Watson 2001; see also Weart 2008).