"Since the late 1970s, it has been recognized that the identification of human effects on climate is inherently a signal-to-noise (S/N) problem [Hasselmann, 1979; Madden and Ramanathan, 1980; Wigley and Jones, 1981; Wigley and Raper, 1990; Allen et al., 1994; Santer et al., 1994, 1995]. The warming signal arising from slow, human-caused changes in atmospheric concentrations of greenhouse gases is embedded in the background 'noise' of natural climate variability. Yet much of the recent public discourse on the reality of a discernible human influence on global climate reflects pervasive confusion regarding the distinctions between short-term climate variability and long-term climate change." ...

"In summary, because of the effects of natural internal climate variability, we do not expect each year to be inexorably warmer than the preceding year, or each decade to be warmer than the last decade, even in the presence of strong anthropogenic forcing of the climate system. The clear message from our signal-to-noise analysis is that multi-decadal records are required for identifying human effects on tropospheric temperature. Minimal warming over a single decade does not disprove the existence of a slowly-evolving anthropogenic warming signal."