ABSTRACT
Global warming may have contributed to this trend, but as with the ENSO, the recent trend is still within the bounds of natural variability. Insufficient trend data is available to conclude that recent global warming has caused the trend toward more frequent positive NAO index readings. The NAO index has, on several occasions since the 1500s, been in the positive range for extended periods.4 Since 2003 the NAO index has returned to near its long-term mean.5
