Historically, James Bay summers are cooler than those experienced by other microclimates of the Saanich Peninsula. This can be attributed primarily to the dominant pattern of onshore and relatively cool southwest sea breezes caused by higher barometric readings over the ocean. For example, the 30-year normal (1971 – 2000) July maximum temperature at Victoria International airport is 21.9 °C, while the average of July 2005 – July 2008 maximums from James Bay Community School is 18.4 °C. Today, however (August 5, 2008), we are experiencing temperatures in the mid twenties, produced by the reverse of this onshore flow: a large ridge of high pressure positioned over the BC interior drives warm northeasterly winds over the Saanich Peninsula.

It is also of interest to note that as I write, Lochside Elementary School in north Saanich is experiencing an 11 Km/hr wind from the NNE, as expected, while James Bay Community School is measuring a wind of 3 Km/hr from the south: a very good example that elements of our microclimate, in this case diurnal onshore flow, can frequently dominate large-scale (macro) weather patterns.

But have James Bay summers actually cooled over the past couple of years? Analyzing the short weather record at James Bay Community School reveals an average maximum temperature for the month of July 2005 of 18.87 °C, compared to 18.19 °C for July 2008. Not a huge difference, and definitely not statistically significant: but enough to prompt further investigation.

Figure 1
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Climate variability in BC is strongly influenced by the Pacific Decadal Oscillation (PDO) and the El Niño Southern Oscillation (ENSO). This NASA Earth Observatory image (Figure 1) depicts the sea surface temperature anomaly between April 14 – 21, 2008. Measured by a scanning radiometer and compared to baseline data collected between 1985 – 1997, warmer than normal areas appear red, cooler than normal blue, and average are white. Clearly visible are the lingering effect of the year-old La Niña and a classic feature of the cool phase of the PDO: cooler water off the coast of north America wrapping around a core of warmer water. Dr. Steven R. Hare, of the University of Washington, first coined the term PDO in 1997 to describe an extensive oscillation of sea surface temperature in the northern Pacific Ocean that varies on a multi-decadal time scale. The other large-scale climate driver is ENSO, a tropical Pacific phenomenon representing the largest climate signal next to the seasonal cycle, and possessing two distinct phases: El Niño the warm phase, and La Niña, the cool phase. Alternation between El Niño and La Niña events is unpredictable, normally occurring every 3 – 7 years, with the individual events lasting 6 – 18 months.

Figure 2
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In contrast, the PDO can remain in the same warm or cool phase for 20 or 30 years, with the last warm phase, which began in 1977, shifting to the cool phase very recently. The accompanying graph (Figure 2) depicts anomalous climate conditions associated with the positive phases of the Pacific Decadal Oscillation and PDO modes since 1900. According to Bill Patzert, an oceanographer and climatologist at NASA’s Jet Propulsion Laboratory (JPL): “The persistence of this large-scale pattern (in 2008) tells us there is much more than an isolated La Niña occurring in the Pacific Ocean.” This cool phase of the PDO will have significant ramifications. It will intensify La Niña events, moderate the impact El Niño events, significantly affect the productivity of marine ecosystems, and alter global land temperature patterns — conceivably cooling James Bay slightly for the foreseeable future. Recent research by Dr.’s Goshit and Malanson at the University of Iowa supports this view, identifying a high positive correlation with the PDO and winter temperatures in the Northwestern US.

However, Dr. William Hsieh, an eminent scholar at UBC’s Department of Earth and Ocean Sciences, cautioned against speculating about the connection between the PDO and weather in BC: "The long-term behavior of the PDO is presently not all that clear, unlike the 1950s to 1970s, when it was cold, and late 1980s to late 1990s when it was warm." Hsieh confirmed that the PDO is in a cold phase, but that “there is no clear evidence to link that to atmospheric temperatures.” A high positive correlation between temperature and the PDO can indeed indicate a causal relationship, but there could exist other underlying factors of which we are unaware.

Figure 3
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If lower sea surface temperatures (SST) off the coast of North America, which characterize the cool mode of the PDO, do indeed translate into somewhat cooler, albeit muted, local and regional temperatures, the longer-term climate change signal becomes masked — more difficult to detect and quantify (Figure 3). Climate scientist and oceanographer Josh Willis of JPL concludes that: “These natural climate phenomena can sometimes hide global warming caused by human activities. Or they can have the opposite effect of accentuating it.” This underscores the importance of collecting consistent and long-term weather records, as only data records that span at least one full cycle of the PDO will reveal the coherent “signal” of climate change that is contained within all natural climate variability.

References
BC Ministry of Environment: http://www.env.gov.bc.ca/air/climate/indicat/appendix.html
BC Climate: Rod Chilton: http://www.bcclimate.com
Goshit, Sunday D. and George P. Malanson. “Patterns of Correlation between the Pacific Decadal Oscillation and the Climate of Glacier National Park, MT.” Department of Geography, University of Iowa. In preparation.
http://www.widernet.org/sunday/researchpaper.htm
Hare, Stephen R. and Nathan J. Mantua. “An historical narrative on the Pacific Decadal Oscillation, interdecadal climate variability and ecosystem impacts.” 20th NE Pacific Pink and Chum workshop Seattle, WA, 22 March 2001.
http://www.iphc.washington.edu/Staff/hare/html/papers/pcworkshop/pcworkshop.pdf
NASA Earth Observatory: http://earthobservatory.nasa.gov
Victoria Weather Network: http://www.victoriaweather.ca/

Figures
1. Courtesy NASA – Earth Observatory
2. Courtesy Stephen R. Hare, University of Washington: Adapted and updated from Mantua et al. (1997)
3. Courtesy Canadian Institute for Climate Studies