It's not as if we didn't already assume this was happening, but scientists have been reluctant to draw a definitive line. But the right-wingers will quickly explain this is simply part of that liberal agenda-driven excuse for science:

Natural variability alone cannot explain the extreme weather pattern that has driven both the record-setting California drought and the cooler weather seen in the Midwest and East this winter, a major new study finds.

We’ve reported before that climate scientists had predicted a decade ago that warming-driven Arctic ice loss would lead to worsening drought in California. In particular, they predicted it would lead to a “blocking pattern” that would shift the jet stream (and the rain it could bring) away from the state — in this case a “Ridiculously Resilient Ridge” of high pressure.

A new study in Geophysical Research Letters (subs. req’d) takes the warming link to the California drought to the next level of understanding. It concludes, “there is a traceable anthropogenic warming footprint in the enormous intensity of the anomalous ridge during winter 2013-14, the associated drought and its intensity.”

The NASA-funded study is behind a pay wall, but the brief news release, offers a simple explanation of what is going on. The research provides “evidence connecting the amplified wind patterns, consisting of a strong high pressure in the West and a deep low pressure in the East [labeled a 'dipole'], to global warming.” Researchers have “uncovered evidence that can trace the amplification of the dipole to human influences.”