Dr. Richard Dewey, Associate Director, Science
Updated: September 1, 2015
The surface waters of the Northeast Pacific started warming in 2013 and now, in mid 2015, remain significantly warmer than at any time over the last few decades. By January 2014, the area and intensity of this warm anomaly had reached its maximum. Howard Freeland (Institute of Ocean Sciences) constructed a map of sea surface temperature anomaly (SSTa) for January 2014 (using the Reynolds SST data set) showing a region of warm temperature anomalies exceeding 4 standard deviations above the mean. He achieved the same result when using independent Argo float data. The area exceeding 3 standard deviations covered an area of more than 1000 km2. To put this in perspective, such an anomalous event would be expected less than once per millennium (<0.1%)! By the fall of 2014 this warm pool of surface water had shifted eastward from the central Gulf of Alaska, and by late 2014 and into early 2015, was blanketing the entire west coast of North America (Figure 1, shown above). Although the extent and the mechanisms and dynamics responsible are still being assessed, there is a growing consensus as to some of the contributing factors that may have led to the development of these warm Northeast Pacific conditions, and a growing awareness of the significance (see for example Chris Mooney’s piece in the Washington Post).
By the spring of 2015 the NOAA El Nino prediction center announced that we are finally (after nearly a year of speculation) entering into an El Nino cycle. Although El Nino is now considered a rather global phenomina, it has a nucleus and primary signals in the western and central equatorial Pacific. The dynamics of an El Nino are related to a strong coupling between the atmosphere and upper ocean in the western equatorial Pacific. When the easterly trade winds slacken, the elevated warm surface waters in the western equatorial Pacific can surge eastward along the equator