Because of large natural
variability, the first approach results in an outcome suggesting that it is appropriate to conclude that there is no increase in
precipitation by human influences,
although the correct interpretation is that there is simply not enough evidence (not a long enough time series).
Steve Ghan, from the Pacific Northwest National Laboratory, says, «This work confirms what previous cloud modelling studies had suggested: that
although clouds are influenced by many factors, increasing aerosols enhances the
variability of
precipitation, suppressing it when
precipitation is light and intensifying it when it is strong.