Hoerling: 'We can also say with high confidence that no appreciable trend toward either wetter or drier conditions has been observed for statewide average precipitation since 1895' -- 'At present, the scientific evidence does not support an argument that the drought there is appreciably linked to human-induced climate change...In short, the drought gripping California has been observed before. And it has occurred principally because of a lack of rain, not principally because of warmer temperatures...the scientific evidence does not support an argument that human-induced climate change has played any appreciable role in the current California drought.' -- 'The 2012 report on extreme events by the Intergovernmental Panel on Climate Change examined the evidence for regional changes in soil moisture since 1950, and made the following assessment for western North America: 'No overall or slight decrease in dryness since 1950; large variability; large drought of the 1930s dominates.'
A 2013 report by the I.P.C.C. reaffirmed that finding and concluded: “Recent long-term droughts in western North America cannot definitively be shown to lie outside the very large envelope of natural precipitation variability in this region…’