Clarifying the Changing Climate in Kamloops

There is a lot of confusion as to how, and in many cases -- if, the climate across Canada is changing. Unfortunately, many of the public discussions by the academic and government communities are confusing or even incorrect.

As yet another example of problematic science communication, in June of last year Peter Tsigaris -- an associate professor and chair of the School of Business and Economics at Thompson Rivers University -- wrote a letter to a now defunct local newspaper indicating that "Signs point to warmer Kamloops." In his analysis, Tsigaris compares temperatures and precipitation "for the recent period 2001 to 2012 relative to a base period 1951 to 1980, which is used in climate change studies." Why choose the 1951-1980 period as a base? It is a poor base, and if we want to see if Kamloops' climate is changing, we should be looking for statistically significant trends over long periods of time. Just comparing a recent 12-year period to an arbitrary 30-year period at some point in the past doesn't provide us with many -- if any -- meaningful insights into whether the climate is changing at Kamloops, and if so, how. We'll start with this statement:

"First, our summers have gotten warmer during the 2001 to 2012 period relative to the base period. No surprise here as we all are feeling the recent heat. But how warmer has it gotten? The average summer temperature has significantly increased from 19.45°C during base period to 20.76°C measured during the 2001 to 2012 period. Kamloops is now on average 1.3°C warmer during the summer months of June, July and August relative to the base period."

---

The 1951-1980 period is the coldest 30-year decadal period (i.e., 1901-1930, 1911-1940, 1921-1950 ... up to 1981-2010) in Kamloops since records began in 1897. Thus, using this as a "base period" gives the appearance of cherry-picking, since it yields the largest possible increase between the current period and an arbitrary 30-year long decadal "base period." A more rigorous approach is to look at the trend in average summer temperatures for Kamloops since 1897. The trend is significant, and increasing, but at only 0.6°C per century. A small rate of increase. And during the last 30 years, there is no significant trend in summer temperatures whatsoever. This claim by Tsigaris also requires testing:

"Precipitation on average has not changed ... winters have become drier as precipitation (rain and snow) has fallen significantly from an average of 26.6 mm per month during the base period to 19 mm per month for 2001 to 2012 ... a significant increase in the spring precipitation relative to the base period is occurring. The average precipitation in the base period is 12.7 mm per month and increases to 19.3 mm per month for the recent period. What does all this mean in terms of impact? Precipitation is shifting from winter to spring. This can have implications for flooding, if in the surrounding mountains precipitation increases in the future."

Incorrect. There is a statistically significant increasing trend in annual precipitation at Kamloops since records began in the late 1800s. During the last 30 years, there is a significant declining trend. In other words, annual precipitation trends in this area are complex. The amount of precipitation has significantly increased overall during the past 120 years, but in recent decades it is declining. Precipitation on average has indeed changed in Kamloops. Winters have become drier? Not since 1897, as there is no significant trend over this period, nor is there a significant trend in winter precipitation over the past 30 years. Spring is getting wetter? Not anymore. Over the past 30 years, there is absolutely no sign of a significant trend in spring precipitation. There is almost a perfect non-correlation in spring precipitation during the last three decades, and the correlation is negative (drier), not positive (wetter). There is a significant trend towards wetter springs since 1897, but that wetting trend stopped long ago and the past few decades have not seen springtime getting any wetter in the Kamloops region. This is a perfect example of where the devil is in the climate details. Claims that "summer is not only warming but so is winter and with an even larger magnitude" do not appear to be true, either. With no significant trend over the past 30 years in either summer or winter temperatures, neither is currently warming. Warming is a present tense term, and since climate scientists often use 30 year periods to assess a changing climate, if there has been no significant increase in temperatures during these seasons for at least the last three decades, they are not "warming." These seasons warmed in the past, but stopped warming long ago. Overall, what we see in Kamloops is a classic example of how science should not be communicated to the public, particularly by those in the academic system. In order for the public to make rational choices on environmental policies, they need to know the real trends (or lack thereof) and how they correlate -- or fail to correlate -- with atmospheric greenhouse gas concentrations.