The study released by the online edition of the peer-reviewed journal Proceedings of the National Academy of Sciences does not question global warming, but argues there is evidence that in at least one place, local winds are a more important factor explaining ocean warming than greenhouse gases. The authors ... have not established the causes of these atmospheric pressure variations. [...] claims that the observed temperature increases are due primarily to 'natural' processes are suspect and premature, at best. Johnstone and co-author Nathan Mantua, a research scientist with the NOAA Fisheries Service in Santa Cruz, California, pointed to the fact that one steep ocean warming period from 1920 to 1940 predates the big increases in greenhouse gases, and an ocean cooling period from 1998 to 2013 came while global average temperatures were at or near all-time highs.