Man-made global warming seems to have contributed to the extreme Californian drought in recent months.

Simon Wang of Utah State University in Logan and his colleagues re-analysed meteorological records and found that the ongoing dry spell is linked to changes in large-scale atmospheric pressure and circulation patterns. These typically occur over North America in the years before El Niño events — the occasional warming of the tropical Pacific Ocean.

Simulations show that atmospheric conditions that tend to cause intense drought in California have become more frequent since 1970 as a result of increased greenhouse-gas concentrations. Projections suggest that future droughts in California will be even more severe, the authors warn.

Geophys. Res. Lett. http://doi.org/sfs (2014)